Characterization of Stratospheric Aerosol Distributions during the Volcanically Quiescent Period of 1998-2004

Cite this Article

YANG Jing-Mei, ZONG Xue-Mei, WANG Pu-Cai. Characterization of Stratospheric Aerosol Distributions during the Volcanically Quiescent Period of 1998-2004. Atmospheric and Oceanic Science Letters, 2014, 7(4): 291-296 Copy to clipboard

Permissions

This is an Open Access article under the terms of CCAL.

Characterization of Stratospheric Aerosol Distributions during the Volcanically Quiescent Period of 1998-2004

YANG Jing-Mei, ZONG Xue-Mei, WANG Pu-Cai

Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Abstract

The Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction profiles at 1020 nm were used to study the distribution characteristics of stratospheric aerosols during the volcanically quiescent period of 1998-2004. The stratospheric aerosol distributions exhibited hemispheric asymmetry between the Northern Hemisphere (NH) and the Southern Hemisphere (SH). In the lower stratosphere below 20 km, the zonal averaged aerosol optical depths in the NH were higher than those of the corresponding SH; whereas at higher altitudes above 20 km, the optical depths in the SH- except the equatorial region-were higher than those of the NH. At 0-10°N and 10-20°N, the stratospheric aerosol optical depth (SAOD) exhibited larger values in boreal winter and lower values in the spring and summer; at 0-10°S and 10-20°S, the SAOD presented small seasonal variations. At 30-40°N, the SAOD presented larger values in the boreal fall and winter and lower values in the spring and summer; while at 30-40°S, the SAOD exhibited larger values in the austral winter and early spring and lower values in the summer and fall. These characteristics can mainly be attributed to the seasonal cycle of the dynamic transport, and the effects of the buildup and breakdown of the polar vortex. At 50-60°S, the SAOD exhibited extremely high values during austral winter associated with the Antarctic polar vortex boundary; at 50-60°N, the SAOD also exhibited larger values during the boreal winter, but it was much less obvious than that of its southern counterpart.

Keyword: aerosol; stratosphere; distribution; optical depth

Show Figures

1 Introduction

Stratospheric aerosols have been recognized as playing an important role in the climate system by influencing the radiative and chemical balance of the atmosphere (e.g., Hofmann and Solomon, 1989; McCormick et al., 1995; Hu and Shi, 1998). Therefore, a reliable characterization of the global distribution of stratospheric aerosols is necessary for a correct understanding and modeling of stratospheric processes. During the last two decades, stratospheric aerosol properties have been observed and studied by many authors (e.g., Brogniez et al., 1996; Wu et al., 2001; Bingen et al., 2006), and several studies were devoted to the description of stratospheric aerosol distributions over different time periods and locations (e.g., Hitchman et al., 1994; Choi et al., 1998; Barnes and Hofmann, 2001; Wang et al., 2004; Padma Kumari et al., 2006; Niwano et al., 2009; Parameswaran et al., 2010; Sunilkumar et al., 2011; Liu et al., 2012; Yang, 2012).

Since the late 1990s, stratospheric aerosols have been characterized by relatively steady levels because of the lack of major volcanic eruptions after the Pinatubo eruption in June 1991 ( Thomason et al., 2008). These steady levels may represent a volcanically quiescent stratosphere and are often referred to as "background stratospheric aerosol levels" ( Deshler et al., 2006). This quiescent period has provided an opportunity to study the stratospheric aerosol distributions under volcanically quiescent conditions. Parameswaran et al. (2010) studied the seasonal variation of aerosol extinction in the upper troposphere and lower stratosphere in the region (0-30°N, 70-90°E) using lidar and the Stratospheric Aerosol and Gas Experiment (SAGE) II observations during 1998-2003. They reported that the annual variation of particulate optical depth in the upper troposphere region showed relatively low values during winter and high values during summer, while the optical depth in the lower stratosphere region had relatively high values during winter and low values during summer. Liu et al. (2012) analyzed SAGE II data over 60°S-60°N for the period 1998-2004, and noted that the seasonal means of aerosol extinctions in the lower stratosphere were typically higher in winter/spring than in summer/fall. To better understand the distribution behavior of the stratospheric aerosol layer during volcanically quiescent periods, quantitative descriptions of global-scale aerosol distributions are necessary. In this paper we examine the stratospheric aerosol distribution and seasonal variation characteristics during the volcanically quiescent period of 1998-2004. We present calculations of the zonal-averaged aerosol optical depth for different altitude levels based on SAGE II 1020-nm aerosol extinction data, and analyze the distributions and seasonal variations of stratospheric aerosols over 10° latitude intervals from 60°S to 60°N.

2 Data and method

The SAGE II measurements provided the vertical profiles of aerosol extinction coefficients at four wavelengths (1020, 525, 452, and 386 nm) from October 1984 to August 2005 ( McCormick et al., 1979; McCormick, 1987; Chu et al., 1989). The profile dataset has near global coverage (80°S-80°N) with a vertical resolution of 0.5 km. The sensitivity study by Thomason et al. (2008) indicated that the bias errors for SAGE II 1020-nm aerosol extinction measurements under non-volcanic conditions were less than 5% from the tropopause to 30 km. Comparisons by Hervig and Deshler (2002) showed that the mean differences between SAGE II and balloon-borne optical particle counters were within 5%-20%. Detailed validations by many other authors (e.g., Russell and McCormick, 1989; Kent et al., 1994; Reeves et al., 2008) have also demonstrated that the SAGE II aerosol extinction profiles are reliable and accurate, particularly for the 1020-nm channel.

In this study, we used SAGE II (version 6.2) 1020-nm aerosol extinction profile data from January 1998 to December 2004. In data processing, the measurement errors for each profile, also provided by the SAGE II data, were checked for each altitude level, and the data with measurement error exceeding 30% were removed. For all the profiles, the extinction value was examined. If it was within 4 km of the tropopause level and exceeded four times the standard deviation plus the zonal mean values, the data were considered to be affected by clouds and thus removed.

To obtain a representative stratospheric aerosol distribution pattern for different latitude bands, the zonal- averaged monthly mean aerosol extinction profiles were calculated by averaging every 10° of latitude from 60°S to 60°N for each month during the period 1998-2004. The zonal-averaged annual mean extinction profiles used in the study were computed by averaging the 12 monthly mean profiles. Besides the extinction data, we also use aerosol optical depth to describe the stratospheric aerosol distribution pattern.

The aerosol optical depth ( τ) for the altitude region z1- z2 was calculated as follows:

, (1)

where β_a ( z) is the aerosol extinction coefficient at altitude z.

Using Eq. (1), the zonal-averaged aerosol optical depth can be calculated by integrating the zonal-averaged extinction coefficients between the two specified height levels.

3 Results and discussion

3.1 Zonal-averaged annual mean stratospheric aerosol distributions

Figure 1 shows the vertical profiles of the zonal- averaged annual mean SAGE II 1020-nm aerosol extinction coefficients for each 10° latitude band during the period 1998-2004 in the Northern Hemisphere (NH) and Southern Hemisphere (SH). The zonal-averaged annual mean tropopause heights and the one standard deviation values for each latitude band are also shown in Figs. 1a and 1b. These figures show that, in both hemispheres, the aerosol extinction coefficients at altitudes above 20 km decreased monotonically with latitudes and, as expected, the aerosol extinction coefficients decreased with the increase in altitude. These extinction profiles are consistent with the reference aerosol distributions presented by McCormick et al. (1996), and are believed to represent typical aerosol vertical distributions during volcanically quiescent periods. To minimize the effects of the tropo-pause height variation and cloud contamination, the lowest bounds chosen in the following analysis were 2 km above the zonal-averaged tropopause heights.

gives the zonal-averaged annual mean aerosol optical depths and the one standard deviations within the altitude ranges from 2 km above the tropopause ( H_T+2) to 20 km, 20-40 km, 26-40 km, and H_T+2 to 40 km for each latitude band. The zonal-averaged tropopause heights are also given. Table 1 shows that the zonal averaged aerosol optical depths in the lower stratosphere below 20 km increased with the increase in latitude, while the optical depth values above 20 km levels decreased with the increase in latitude. This distribution pattern is associated with the transport effects of the Brewer-Dobson circulation in the lower stratosphere ( Brewer, 1949; Dobson, 1956). The Brewer-Dobson circulation, which is driven by extratropical wave forcing in the middle atmosphere ( Holton et al., 1995), consists of an upward motion in the tropics, poleward and downward flow in the midlatitudes, and subsidence at high latitudes. Table 1 also shows that there is an obvious asymmetry in aerosol distribution between the NH and the SH. At the lower stratosphere below 20 km, the zonal-averaged aerosol optical depth values in the NH were 3.6% to 6.8% higher than the values of the corresponding SH. This distribution behavior can be explained by the stronger upward mass transport from the upper troposphere into the lower stratosphere in the northern tropics and more effective meri-dional poleward and downward transport in the northern midlatitude lower stratosphere regions. At the altitude level above 20 km, the zonal mean aerosol optical depths in the SH-except the equatorial region where the NH and SH share approximately the same optical depth values-were 2.7% to 13.7% higher than in the NH. This distribution is due to the more pronounced rising motions in the SH lower stratosphere.

	Figure Option View Download New Window
	Figure 1 Zonal-averaged annual mean SAGE II 1020-nm aerosol extinction profiles for each 10° latitude band from (a) 0-60°N and (b) 0- 60°S for 1998-2004. The observed heights of the tropopause are indicated by the vertical bars (one standard deviation) using the same color as the corresponding extinction profiles.

Table 1 Aerosol optical depths ( τ) ( multiplied by 1000) within the altitude ranges from 2 km above the tropopause ( H_T+2) to 20 km, 20-40 km, 26-40 km, and H_T+2 to 40 km for each latitude band. The corresponding standard deviations ( σ) and the zonal-averaged tropopause heights ( H_T) are also listed.

Table 1 also shows that in the tropical lower stratosphere, the standard deviations in the NH were higher than in the SH, whereas in the tropical higher altitude region (> 26 km), the standard deviation values were higher in the SH than in the NH, revealing that the NH exhibited greater variability in aerosol loading in the lower stratosphere, while the SH had more pronounced variability at altitudes above 26 km. Furthermore, Table 1 shows that in the southern high-latitude band of 50-60°S, the standard deviation values for H_T+2-20 km and 20-40 km were obviously higher than those of the corresponding NH, suggesting a greater seasonal variability at the southern high-latitude stratosphere. The seasonal variation behavior of the stratospheric aerosol layer for different latitude bands is discussed in the next section.

3.2 Latitudinal and seasonal variations

Figure 2 presents the zonal-averaged monthly mean aerosol optical depths for different altitude ranges for the tropics (Figs. 2a and 2b), midlatitudes (Fig. 2c) and high latitudes (Fig. 2d). The figures show that in the northern tropical latitude bands 0-10°N and 10-20°N, the stratospheric aerosol optical depths (SAODs) (integrated aerosol extinction coefficients from 2 km above the tropo-pause to 40 km) displayed a seasonal variation with larger values in the northern winter (December-February) and lower values in the spring and summer (April-July). In the tropical region, the aerosol loading in the lower stratosphere is mainly associated with the amount of aerosol entering the stratosphere. The quantities studies by Rosenlof and Holton (1993) and Rosenlof (1995) revealed that the upward mass flux in the tropics across the 100 mb surface (about the height of the tropical tropopause) is much stronger in the northern winter than in the summer, and these processes normally lead to a wintertime maximum and summertime minimum in aerosol loading at the lower stratosphere levels. The springtime lower aerosol loadings in the northern tropical regions shown in Figs. 2a and 2b can be explained by the meridional transport effects. During boreal spring, after the breakdown of the Arctic polar vortex, the confined aerosol in the tropical region spread poleward, resulting in a decrease in aerosol amounts in the lower stratosphere. In the southern tropical latitude bands 0-10°S and 10-20°S, the SAOD values exhibited small seasonal variations with relatively larger values in December to February. The larger seasonal amplitude at 0-10°N and 10-20°N than at 0-10°S and 10-20°S can be explained by the following two reasons: (1) Larger amounts of aerosols were brought up to the northern tropics upper troposphere by the Asian summer monsoon and other strong convective systems during boreal summer, causing the high aerosol concentrations in the upper troposphere region, as noted by Parameswaran et al. (2010), and these aerosols were further transferred into the stratosphere by the stronger upward convention wind during boreal winter, thus creating a higher seasonal maximum of aerosol loading in the northern stratosphere during the winter. (2) The meridional dispersion was more efficient during boreal spring due to the breakdown of the Arctic polar vortex, resulting in the lower seasonal minimum of aerosol loading in the northern tropical lower stratosphere during the late spring and summer.

	Figure Option View Download New Window
	Figure 2 Zonal monthly mean SAGE II 1020-nm aerosol optical depths within the altitude ranges from 2 km above the tropopause ( H_T+2) to 40 km, 20-40 km, and 26-40 km for the latitude bands of (a) 0°-10°, (b) 10°-20°, (c) 30°-40°, and (d) within the altitude ranges from H_T+2 to 40 km, 15-40 km, and H_T+2 to 15 km for the latitude band of 50°-60°.

Figure 2b also shows that the optical depths above 26 km (26-40 km) for both hemispheres were characterized by higher values in the local fall, and the amplitude of the seasonal cycle was larger in the SH than in the NH. This is in general agreement with the studies of Niwano et al. (2009), and can be explained by the ascent of the mean meridional aerosol transport in the local summer and the descent in the local winter; and the ascent of the mean meridional circulation has a larger seasonal amplitude in the SH ( Niwano et al., 2009).

For the midlatitude bands shown in Fig. 2c, the SAOD in the northern 30-40°N band is characterized by seasonal variations with larger values in the local fall and winter and lower values in the spring and summer. This characterization was primarily related to the seasonal cycle of the dynamic aerosol transport from the tropics toward the polar regions, which was stronger toward the winter hemisphere than toward the summer hemisphere ( Kent and McCormick, 1984). The fall month high optical depth values can be explained by the effects of the polar Arctic vortex. In the late summer (August), when the Arctic polar vortex began to build up, the horizontal aerosol trans-port from the midlatitudes to the polar region was suppressed, causing an increase in aerosol concentration in the northern lower stratosphere during the fall months. In the southern 30-40°S band, the seasonal variation of the SAOD exhibited larger values during the local winter and early spring and lower values during the summer and fall. These variations were also primarily related to the stronger poleward and downward aerosol transport during the winter, and the effects of the Antarctic polar vortex. During austral winter and early spring, the meridional aerosol transport to the polar region was inhibited by the strong Antarctic polar vortex, and the aerosol loading was enhanced, while after the breakdown of the polar vortex in late October and early November, the aerosol spread poleward, resulting in a decrease in aerosol concentrations during the austral summer months.

It is worth noting that our results of aerosol seasonal variation are different from the results of higher values in winter/spring and lower values in summer/fall obtained by Liu et al. (2012) using the same SAGE II data set of 1998-2004. This difference could be explained by the fact that the data used in our study excluded data considered to be affected by clouds, whereas the data used by Liu et al. (2012) included the data contaminated by clouds.

For the high-latitude bands shown in Fig. 2d, the aerosol optical depth between 15 km and 40 km in the southern 50-60°S latitude band exhibited extremely high values during the austral winter (June-August), while the aerosol optical depth below 15 km remained relatively constant. Figure 2d shows that the main contributor to the high SAOD values during austral winter was the enhan-cement of aerosol amounts in the altitudes above 15 km. This aerosol pattern is associated with the Antarctic polar vortex boundary. As discussed in detail by Hartmann et al. (1989), the polar vortex acts as a barrier inhibiting the horizontal transport from lower latitudes. As the Antarctic polar vortex intensifies during austral wintertime, the poleward aerosol transport above the base of the vortex (about 15 km) is suppressed, inducing an enhancement in aerosol loading outside the vortex. At the lower stratosphere below 15 km levels, the horizontal aerosol trans-port occurs freely, and the enhancement of aerosol loading does not occur. In the northern 50-60°N latitude band, a high stratospheric aerosol loading can also be seen during the boreal winter, but it is much less obvious than that of its southern counterpart, since the Arctic polar vortex is not so pronounced and persistent as the Antarctic one.

4 Conclusions

In this study, we used SAGE II 1020-nm aerosol extinction profile data to describe the distribution characteristics of the stratospheric aerosol in the different altitude levels during the volcanically quiescent period of 1998- 2004. We have shown that the zonal-averaged annual mean aerosol optical depths in the lower stratosphere below 20 km increased with the increase in latitude, while the optical depth values above 20 km levels decreased with the increase in latitude. We have also shown that the zonal-averaged stratospheric aerosol distributions presented a hemispheric asymmetry between the NH and the SH.

The seasonal variation of the stratospheric aerosols also exhibited hemispheric asymmetry between the NH and the SH. At 0-10°N and 10-20°N, the SAOD presented larger values in the northern winter (December-February) and lower values in the spring and summer (April-July), which was mainly due to the stronger upward aerosol transport from the troposphere into the stratosphere during the northern winter. At 0-10°S and 10-20°S, the SAOD values exhibited small seasonal variations with rela-tively larger values in December to February. The seasonal variation differences between the NH and the SH were mainly associated with the differences in the amount of aerosol entering the tropical stratosphere and the meridional transport effects.

At 30-40°N, the SAOD exhibited larger values in the local fall and winter, and lower values in the spring and summer; whereas at 30-40°S, the seasonal variation of the SAOD presented larger values in the local winter and early spring and lower values in the summer and fall. These variations were mainly associated with the seasonal cycle of transport processes, and the effects of the buildup and breakdown of the polar vortex in both hemispheres.

At 50-60°S, the SAOD presented quite a strong seasonal variation with pronounced larger values in austral winter (June-August) associated with the Antarctic polar vortex boundary. At 50-60°N, the SAOD also exhibited larger values during boreal winter, but it was much less obvious than that of its southern counterpart.

Acknowledgements. The authors wish to acknowledge the National Aeronautics and Space Administration (NASA) Langley Research Center for the SAGE II aerosol data. This work was supported by the National Basic Research Program of China (Grant No. 2013CB955801), the National Natural Science Foundation of China (Grant No. 41275047), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA05100300).

Reference

1	Barnes J. E. , D. J. Hofmann, 2001: Variability in the stratospheric background aerosol over Mauna Loa Observatory, Geophys. Res. Lett. , 28, 2895-2898, doi: DOI:10.1029/2001GL013127.
2	Bingen C. , D. Fussen, F. Vanhellemont, 2006: A review of stratos-pheric aerosol characterization, Adv. Space Res. , 38, 2433-2445.
3	Brewer A. W. , 1949: Evidence for a world circulation provided by the measurements of helium and water vapor distribution in the stratosphere, Quart. J. Roy. Meteor. Soc. , 75, 351-363.
4	Brogniez C. , J. Lenoble, M. Herman, et al. , 1996: Analysis of two balloon experiments in coincidence with SAGE II in case of large stratospheric aerosol amount: Post-Pinatubo period, J. Geophys. Res. , 101(D1), 1541-1552, doi: DOI:10.1029/95JD01640.
5	Choi W. , W. B. Grant, J. H. Park, et al. , 1998: Role of the quasi-biennial oscillation in the transport of aerosols from the tropical stratospheric reservoir to midlatitudes, J. Geophys. Res. , 103(D6), 6033-6042, doi: DOI:10.1029/97JD03118.
6	Chu W. P. , M. P. McCormick, J. Lenoble, et al. , 1989: SAGE II inversion algorithm, J. Geophys. Res. , 94, 8339-8351.
7	Deshler T. , R. Anderson-Sprecher, H. Jager, et al. , 2006: Trends in the nonvolcanic component of stratospheric aerosol over the period 1971-2004, J. Geophys. Res. , 111, D01201, doi: DOI:10.1029/2005JD006089.
8	Dobson, G. M. B. , 1956: Origin and distribution of the polyatomic molecules in the atmosphere, Proc. Roy. Soc. London, A236, 187-193.
9	Hartmann D. L. , K. R. Chan, B. L. Gary, et al. , 1989: Potential vor-ticity and mixing in the south polar vortex during spring, J. Geo-phys. Res. , 94(D9), 11625-11640, doi: DOI:10.1029/JD094iD09p11625.
10	Hervig M. , T. Deshler, 2002: Evaluation of aerosol measurements from SAGE II, HALOE, and balloonborne optical particle counters, J. Geophys. Res. , 107, D34031, doi: DOI:10.1029/2001JD000703.
11	Hitchman M. H. , M. Mckay, C. R. Trepte, 1994: A climatology of stratospheric aerosol, J. Geophys. Res. , 99, 20689-20700.
12	Hofmann D. J. , S. Solomon, 1989: Ozone destruction through heterogeneous chemistry following the eruption of El Chichón, J. Geophys. Res. , 94, 5029-5041.
13	Holton J. R. , P. H Haynes, M. E. McIntyre, et al. , 1995: Stratosphere-troposphere exchange, Rev. Geophys. , 33, 403-439.
14	Hu R. M. , G. Y. Shi, 1998: Horizontal two-dimensional distribution of radiative forcing and climate effect due to stratospheric aerosol, Chinese J. Atmos. Sci. (in Chinese), 12(1), 8-24.
15	Kent G. S. , M. P. McCormick, 1984: SAGE and SAM II measurements of global stratospheric aerosol optical depth and mass loading, J. Geophys. Res. , 89(D4), 5303-5314, doi: DOI:10.1029/JD089iD04p05303.
16	Kent G. S. , M. P. McCormick, P. -H. Wang, 1994: Validation of stratospheric aerosol and gas experiments I and II satellite aerosol optical depth measurements using surface radiometer data, J. Geophys. Res. , 99(D5), 10333-10339, doi: DOI:10.1029/94JD00167.
17	Liu Y. , X. Zhao, W. Li, et al. , 2012: Background stratospheric aerosol variations deduced from satellite observations, J. Appl. Meteor. Climatol. , 51, 799-812.
18	McCormick M. P. , 1987: SAGE II: An overview, Adv. Space Res. , 7, 219-226.
19	McCormick M. P. , P. Hamill, T. J. Pepin, et al. , 1979: Satellite studies of the stratospheric aerosol, Bull. Amer. Meteor. Soc. , 60, 1038-1046.
20	McCormick M. P. , L. W. Thomason, C. R. Trepte, 1995: Atmospheric effects of the Mt Pinatubo eruption, Nature, 373, 399-404, doi: DOI:10.1038/373399a0.
21	McCormick M. P. , P. -H. Wang, M. C. Pitts, 1996: Background stratospheric aerosol and polar stratospheric cloud reference models, Adv. Space Res. , 18, 155-177.
22	Niwano M. , S. Hayashida, H. Akiyoshi, et al. , 2009: Seasonal cycles of stratospheric aerosol and gas experiment II near- background aerosol in the lower stratosphere, J. Geophys. Res. , 114, D14306, doi: DOI:10.1029/2008JD009842.
23	PadmaKumari B. , A. L. Londhe, D. B. Jadhav, et al. , 2006: Seasonal variability in the stratospheric aerosol layer in the current volcanically-quiescent period over two tropical stations in India using the twilight sounding method, Geophys. Res. Lett. , 33, L12807, doi: DOI:10.1029/2006GL026087.
24	Parameswaran K. , B. V. Thampi, S. V. Sunilkumar, 2010: Latitudinal dependence of the seasonal variation of particulate extinction in the UTLS over the Indian longitude sector during volcanically quiescent period based on Lidar and SAGE-II observations, J. Atmos. Sol. -Terr. Phys. , 72, 1024-1035, doi: DOI:10.1016/
25	j. jastp. 2010. 06. 004.
26	Reeves J. M. , J. C. Wilson, C. A. Brock, et al. , 2008: Comparison of aerosol extinction coefficients, surface area density, and volume density from SAGE II and in situ aircraft measurements, J. Geophys. Res. , 113, D10202, doi: DOI:10.1029/2007JD009357.
27	Rosenlof K. H. , 1995: Seasonal cycle of the residual mean meri-dional circulation in the stratosphere, J. Geophys. Res. , 100(D3), 5173-5191, doi: DOI:10.1029/94JD03122.
28	Rosenlof K. H. , J. R. Holton, 1993: Estimates of the stratospheric residual circulation using the downward control principle, J. Geophys. Res. , 98(D6), 10465-10479, doi: DOI:10.1029/93JD00392.
29	Russell P. B. , M. P. McCormick, 1989: SAGE II aerosol data validation and initial data use: An introduction and overview, J. Geophys. Res. , 94, 8335-8338.
30	Sunilkumar S. V. , K. Parameswaran, B. V. Thampi, et al. , 2011: Variability in background stratospheric aerosols over the tropics and its association with atmospheric dynamics, J. Geophys. Res. , 116, D13204, doi: DOI:10.1029/2010JD015213.
31	Thomason L. W. , S. P. Burton, B. -P. Luo, et al. , 2008: SAGE II measurements of stratospheric aerosol properties at non-volcanic levels, Atmos. Chem. Phys. , 8, 983-995.
32	Wang K. C. , W. L. Li, L. J. Bai, 2004: Characteristics of change and transport of aerosols in the middle and upper troposphere and stratosphere over Indian Ocean and China in 1984-2000, J. Appl. Meteor. Sci. (in Chinese), 15(1), 32-40.
33	Wu Y. H. , H. L. Hu, J. Zhou, et al. , 2001: Measurements of stratos-pheric aerosol with L625 Lidar, Acta Opt. Sincia (in Chinese), 21(8), 1012-1015.
34	Yang J. M. , 2012: An empirical method for estimating background stratospheric aerosol extinction profiles over China, Atmos. Oceanic Sci. Lett. , 5(2), 95-101.

2001

3.982

0.0

. 2001, 28(15):2895-2898

Variability in the stratospheric background aerosol over Mauna Loa Observatory

J. E. Barnes andD. J. Hofmann

NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Boulder, CO 80303

> The stratospheric aerosol layer above Mauna Loa Observatory (MLO), Hawaii, has been at low background levels for the past 5 years. This is the first time that an extended non-volcanic background aerosol period has been observed since modern measurements began in the early 1960s. Lidar backscatter at 532 nm shows a distinct maximum in winter and minimum in summer. The five annual cycles have included three easterly phases and two westerly phases of the quasibiennial oscillation (QBO). Differences in aerosol backscatter versus altitude profiles are seen for different QBO phases. There is also a switching of about 25% in the magnitude of the aerosol backscatter on a weekly time scale with varying particle size derived from multiwavelength data. Assumption of a tropical particle source at background suggests that the differing particle regimes are tropical and midlatitude.

... Barnes and Hofmann, 2001 ...

2006

1.183

0.0

. 2006, 38:2433-2445 DOI:10.1016/j.asr.2006.02.061

A review of stratos-pheric aerosol characterization

Abstract We present a general overview of the efforts devoted to the characterization of stratospheric aerosols. After recalling the most important parameters used to characterize aerosols, we present an overview of methods used for retrieving these parameters from radiative measurements. We subsequently review the most important climatological studies developed to characterize stratospheric aerosols, and analyse the main contributions and limitations of these works. Finally, we try to identify current topics of interest and perspectives in the field of aerosol characterization.

... Bingen et al ...

1949

0.0

. 1949, 75(326):351-363

Evidence for a world circulation provided by the measurements of helium and water vapour distribution in the stratosphere

A. W. Brewer M.Sc., A. Inst. P.

> Information is now available regarding the vertical distribution of water vapour and helium in the lower stratosphere over southern England. The helium content of the air is found to be remarkably constant up to 20 km but the water content is found to fall very rapidly just above the tropopause, and in the lowest 1 km of the stratosphere the humidity mixing ratio falls through a ratio of 10—1.

... This distribution pattern is associated with the transport effects of the Brewer-Dobson circulation in the lower stratosphere (Brewer, 1949 ...

1996

3.174

0.0

. 1996, 101(D1):1541-1552

Analysis of two balloon experiments in coincidence with SAGE II in case of large stratospheric aerosol amount: Post-Pinatubo period

C. BrogniezJ. LenobleM. HermanP. LecomteC. Verwaerde

> The stratospheric aerosol layer is regularly monitored since 1979 by satellite experiments as Stratospheric Aerosol Measurement (SAM II) and Stratospheric Aerosol and Gas Experiment (SAGE I and II). The satellite spectral measurements of transmission permit one to obtain the spectral variations of extinction from which the aerosol size distribution may be derived. Several correlative measurements with a balloon-borne polarimeter, Radiomètre Ballon (Radibal), were conducted during the post-El Chichon period to validate the satellite measurements. The radiance and polarization diagrams of the sunlight scattered by the aerosols, measured from the balloon, were analyzed within the primary scattering approximation, and the retrieved aerosol size distribution was compared with the satellite results. Following the eruption of Mount Pinatubo (June 15, 1991), two flights of Radibal were planned to allow a validation in case of large aerosol amount. Because of the importance of the multiple scatterings the usual inversion of the Radibal measurements was no more valid. We propose here an improved scheme to evaluate the coherence of both SAGE II and Radibal that gives excellent results.

... , Brogniez et al ...

1998

3.174

0.0

. 1998, 103(D6):6033-6042

Role of the quasi-biennial oscillation in the transport of aerosols from the tropical stratospheric reservoir to midlatitudes

Wookap ChoiWilliam B. GrantJae H. ParkKwang-Mog LeeHyunah LeeJames M. Russell III

> The temporal evolution of the stratospheric aerosol distribution in the tropical stratospheric reservoir after the eruption of Mount Pinatubo was observed from 1992 to 1995 by the HALOE instrument on the UARS satellite. Since the spatial gradient of aerosol loading is large at the boundaries of the tropical stratospheric reservoir due to the volcanic aerosols, the effect of the meridional circulation on the distribution is seen clearly. The mechanism for dispersal of aerosol in the lower stratosphere from the tropics into midlatitudes strongly depends on the phase of the equatorial zonal wind. The time-latitude crosssections of the normalized distribution of aerosol on isentropic surfaces are used to observe the equatorial variation as well as change in meridional dispersal during the quasibiennial period. Observed tropical stratospheric winds are used with a simple analytical dynamical model to examine transport processes of tracers from the tropics during several phases of the quasibiennial oscillation (QBO) from 1992 to 1995. The Lagrangian meridional circulation in the tropics is consistent with the vertical and meridional velocities correlated with the QBO in the zonal wind. We find that vertical motion plays a crucial role in vertical and subsequent meridional transport. The pattern of meridional divergence derived from the vertical velocity is closely related to the observed HALOE aerosol distributions and their temporal development in the equatorial region. The westerly (easterly) shear phase of the QBO is associated with sinking (rising) motions at the equator and subsequent poleward (equatorward) transport in the lower stratosphere.

... Choi et al ...

1989

3.174

0.0

. 1989, 94(D6):8339-8351

SAGE II inversion algorithm

W. P. ChuM. P. McCormickJ. LenobleC. BrogniezP. Pruvost

> This paper provides a detailed description of the current operational SAGE II multichannel data inversion algorithm implemented at NASA Langley Research Center, Hampton, Virginia. This algorithm is compared to an independently developed inversion algorithm from the Laboratory of Atmospheric Optics, University of Lille, Lille, France. Inverted aerosol and ozone profiles from these two algorithms are shown to be similar within their respective uncertainties.

... Chu et al ...

2006

3.174

0.0

... These steady levels may represent a volcanically quiescent stratosphere and are often referred to as ��background stratospheric aerosol levels�� (Deshler et al ...

1956

0.0

1989

0.0

. 1989, 94(D9):11625-11640

Potential vorticity and mixing in the south polar vortex during spring

D. L. HartmannK. R. ChanB. L. GaryM. R. SchoeberlP. A. NewmanR. L. MartinM. LoewensteinJ. R. PodolskeS. E. Strahan

> A central part of the explanation of the Antarctic ozone hole is the dynamical isolation provided by the intense vortex present over the south polar region until late in the spring. In this paper some fluid dynamical aspects of the Antarctic ozone hole phenomena are investigated, using data collected by the ER-2 aircraft during the Airborne Antarctic Ozone Experiment (AAOE). Analysis of high-resolution potential vorticity and nitrous oxide sections determined from the aircraft data show relatively little evidence of irreversible lateral mixing associated with large-scale disturbances. Less than 10% of the flight legs show evidence of reversed meridional gradients of potential vorticity and nitrous oxide for spatial scales of more than a few degrees of latitude. Correlation studies show that small-scale static stability variations are correlated positively with wind speed and not with relative vorticity, which strongly suggests that these are gravity wave signatures. Smaller-scale variations in nitrous oxide and wind velocity are thus believed to be associated with gravity waves and not to represent lateral mixing which would constitute a significant breach of the dynamical isolation implied by the large-scale potential vorticity gradient. Compositing of wind, potential vorticity, and nitrous oxide relative to the edge of the chemically perturbed region shows an enhancement of the meridional gradient of potential vorticity and nitrous oxide near this boundary at the 450 K potential temperature level. It is argued that this may be caused by the developing ozone concentration gradient producing a strong gradient in solar heating, which in turn drives a steepened potential vorticity gradient, although the temporal sampling provided by the AAOE measurements is not sufficient to prove this hypothesis. Another possible explanation of the enhanced gradients would be gradient steepening through erosion, by lateral mixing on the inner edge of the region of the strong meridional gradients of conserved quantities that define the vortex.

... As discussed in detail by Hartmann et al ...

2002

3.174

0.0

1994

3.174

0.0

. 1994, 99(D10):20689-20700

A climatology of stratospheric aerosol

Matthew H. HitchmanMegan McKayCharles R. Trepte

> A global climatology of stratospheric aerosol is created by combining nearly a decade (1979–1981 and 1984–1990) of contemporaneous observations from the Stratospheric Aerosol and Gas Experiment (SAGE I and II) and Stratospheric Aerosol Measurement (SAM II) instruments. One goal of this work is to provide a representative distribution of the aerosol layer for use in radiative and chemical modeling. A table of decadal average 1μm extinction values is included, extending from the tropopause to 35 km and 80°S to 85°N, which allows estimation of surface area density. We find that the aerosol layer is distinctly volcanic in nature and suggest that the decadal average is a more useful estimate of future aerosol loading than a “background” loading, which is never clearly achieved during the data record. This climatology lends insight into the general circulation of the stratosphere. Latitude - altitude sections of extinction ratio at 1 μm are shown, averaged by decade, season, and phase of the quasi-biennial oscillation (QBO). A tropical reservoir region is diagnosed, with an “upper” and a “lower” transport regime. In the tropics above 22 km (upper regime), enhanced lofting occurs in the summer, with suppressed lofting or eddy dilution in the winter. In the extratropics within two scale heights of the tropopause (lower regime), poleward and downward transport is most robust during winter, especially in the northern hemisphere. The transport patterns persist into the subsequent equinoctial season. Ascent associated with QBO easterly shear favors detrainment in the upper regime, while relative descent and poleward spreading during QBO westerly shear favors detrainment in the lower regime. Extinction ratio differences between the winter-spring and summer-fall hemispheres, and differences between the two phases of the QBO, are typically 20–50%. Dynamical implications of the aerosol distributions are explored, with focus on interhemispheric differences, strong subtropical gradients, and the pronounced annual cycle.

... , Hitchman et al ...

1989

3.174

0.0

. 1989, 94(D4):5029-5041

Ozone destruction through heterogeneous chemistry following the eruption of El Chichón

David J. HofmannSusan Solomon

> It is now well established that heterogeneous reactions provide an important mechanism for Antarctic ozone depletion. Recent laboratory studies suggest that the same reactions that occur on HNO 3 /H 2 O ice clouds in the cold Antarctic stratosphere can also take place on sulfuric acid particles (e.g., volcanic and background aerosols) typical of lower latitudes, albeit at slower rates. The reduction in stratospheric ozone observed at northern mid-latitudes in late 1982 through 1983 following the volcanic eruption of El Chichón is investigated in terms of ozone loss through heterogeneous chemistry on the aerosol which formed in the stratosphere. The rates of the relevant heterogeneous reactions are believed to be critically dependent on (1) the aerosol surface area density and (2) the percent by weight sulfuric acid in the liquid particles. Direct measurements of both of these important quantities for El Chichón aerosol are described and used as a basis for model calculations of their possible effects on ozone and other trace species. The observed volcanic particle surface area reached a maximum at mid-latitudes of about 50 μm 2 cm −3 (above a typical background value of about 0.75) at an altitude of 18–20 km in early 1983. This enhancement of surface area is about the same as that encountered in stratospheric clouds in the Antarctic, suggesting a possible basis for ozone depletion through heterogeneous chemistry. Observations of NO 2 and HNO 3 also suggest that heterogeneous reactions on both background and volcanic aerosol play a significant role in partitioning reactive nitrogen species in middle and high latitudes in winter. It is shown that heterogeneous reactions similar to those occurring in Antarctica may have been responsible for at least a portion of the anomalous ozone reduction observed at mid-latitudes in early 1983.

... , Hofmann and Solomon, 1989 ...

1995

13.906

0.0

. 1995, 33(4):403-439

Stratosphere-troposphere exchange

James R. HoltonPeter H. HaynesMichael E. McIntyreAnne R. DouglassRichard B. RoodLeonhard Pfister

> In the past, studies of stratosphere-troposphere exchange of mass and chemical species have mainly emphasized the synoptic- and small-scale mechanisms of exchange. This review, however, includes also the global-scale aspects of exchange, such as the transport across an isentropic surface (potential temperature about 380 K) that in the tropics lies just above the tropopause, near the 100-hPa pressure level. Such a surface divides the stratosphere into an “overworld” and an extratropical “lowermost stratosphere” that for transport purposes need to be sharply distinguished. This approach places stratosphere-troposphere exchange in the framework of the general circulation and helps to clarify the roles of the different mechanisms involved and the interplay between large and small scales. The role of waves and eddies in the extratropical overworld is emphasized. There, wave-induced forces drive a kind of global-scale extratropical “fluid-dynamical suction pump,” which withdraws air upward and poleward from the tropical lower stratosphere and pushes it poleward and downward into the extratropical troposphere. The resulting global-scale circulation drives the stratosphere away from radiative equilibrium conditions. Wave-induced forces may be considered to exert a nonlocal control, mainly downward in the extratropics but reaching laterally into the tropics, over the transport of mass across lower stratospheric isentropic surfaces. This mass transport is for many purposes a useful measure of global-scale stratosphere-troposphere exchange, especially on seasonal or longer timescales. Because the strongest wave-induced forces occur in the northern hemisphere winter season, the exchange rate is also a maximum at that season. The global exchange rate is not determined by details of near-tropopause phenomena such as penetrative cumulus convection or small-scale mixing associated with upper level fronts and cyclones. These smaller-scale processes must be considered, however, in order to understand the finer details of exchange. Moist convection appears to play an important role in the tropics in accounting for the extreme dehydration of air entering the stratosphere. Stratospheric air finds its way back into the troposphere through a vast variety of irreversible eddy exchange phenomena, including tropopause folding and the formation of so-called tropical upper tropospheric troughs and consequent irreversible exchange. General circulation models are able to simulate the mean global-scale mass exchange and its seasonal cycle but are not able to properly resolve the tropical dehydration process. Two-dimensional (height-latitude) models commonly used for assessment of human impact on the ozone layer include representation of stratosphere-troposphere exchange that is adequate to allow reasonable simulation of photochemical processes occurring in the overworld. However, for assessing changes in the lowermost stratosphere, the strong longitudinal asymmetries in stratosphere-troposphere exchange render current two-dimensional models inadequate. Either current transport parameterizations must be improved, or else, more likely, such changes can be adequately assessed only by three-dimensional models.

... The Brewer-Dobson circulation, which is driven by extratropical wave forcing in the middle atmosphere (Holton et al ...

1998

0.0

... Hu and Shi, 1998) ...

1984

3.174

0.0

. 1984, 89(D4):5303-5314

SAGE and SAM II measurements of global stratospheric aerosol optical depth and mass loading

G. S. KentM. P. McCormick

> Several volcanic eruptions between November 1979 and April 1981 have injected material into the stratosphere. The SAGE and SAM II satellite systems have measured, with global coverage, the 1-μm extinction produced by this material and examples of the data product are shown in the form of global maps of stratospheric optical depth and altitude-latitude plots of zonal mean extinction. These data, and that for the volcanically quiet period in early 1979, have been used to determine the changes in the total stratospheric mass loading. Estimates have also been made of the. contribution to the total aerosol mass from each eruption. It has been found that between early 1979 and mid-1981, the total stratospheric aerosol mass increased from a background level of approximately 570,000 metric tons to a peak of approximately 1,300,000 metric tons.

... This characterization was primarily related to the seasonal cycle of the dynamic aerosol transport from the tropics toward the polar regions, which was stronger toward the winter hemisphere than toward the summer hemisphere (Kent and McCormick, 1984) ...

1994

3.174

0.0

. 1994, 99(D5):10333-10339

Validation of Stratospheric Aerosol and Gas Experiments I and II satellite aerosol optical depth measurements using surface radiometer data

G. S. KentM. P. McCormickP.-H. Wang

> The stratospheric aerosol measurement II, stratospheric aerosol and gas experiment (SAGE) I, and SAGE II series of solar occultation satellite instruments were designed for the study of stratospheric aerosols and gases and have been extensively validated in the stratosphere. They are also capable, under cloud-free conditions, of measuring the extinction due to aerosols in the troposphere. Such tropospheric extinction measurements have yet to be validated by appropriate lidar and in situ techniques. In this paper published atmospheric aerosol optical depth measurements, made from high-altitude observatories during volcanically quiet periods, have been compared with optical depths calculated from local SAGE I and SAGE II extinction profiles. Surface measurements from three such observatories have been used, one located in Hawaii and two within the continental United States. Data have been intercompared on a seasonal basis at wavelengths between 0.5 and 1.0 μm and found to agree within the range of measurement errors and expected atmospheric variation. The mean rms difference between the optical depths for corresponding satellite and surface measured data sets is 29%, and the mean ratio of the optical depths is 1.09.

... Kent et al ...

2012

0.0

... Liu et al ...

... It is worth noting that our results of aerosol seasonal variation are different from the results of higher values in winter/spring and lower values in summer/fall obtained by Liu et al ...

... This difference could be explained by the fact that the data used in our study excluded data considered to be affected by clouds, whereas the data used by Liu et al ...

1987

1.183

0.0

... McCormick, 1987 ...

1979

0.0

... 2 Data and methodThe SAGE II measurements provided the vertical profiles of aerosol extinction coefficients at four wavelengths (1020, 525, 452, and 386 nm) from October 1984 to August 2005 (McCormick et al ...

1995

38.597

0.0

. 1995, 373(6513):399-404

Atmospheric effects of the Mt Pinatubo eruption

... McCormick et al ...

1996

1.183

0.0

. 1996, 18:null-null

Background stratospheric aerosol and polar stratospheric cloud reference models

... These extinction profiles are consistent with the reference aerosol distributions presented by McCormick et al ...

2009

3.174

0.0

. 2009, 114(D14):null-null

Seasonal cycles of Stratospheric Aerosol and Gas Experiment II near-background aerosol in the lower stratosphere

Masanori Niwano 1,5 ,Sachiko Hayashida 2 ,Hideharu Akiyoshi 3 andMasaaki Takahashi 4

1 Frontier Research Center for Global Climate, JAMSTEC, Yokohama, Japan 2 Faculty of Science, Nara Women's University, Nara, Japan 3 National Institute for Environmental Studies, Ibaraki, Japan 4 Center for Climate System Research, University of Tokyo, Kashiwa, Japan 5 Now at Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., Takarazuka, Japan.

> [1] Extinction data from the Stratospheric Aerosol and Gas Experiment (SAGE) II in the lower stratosphere were analyzed for seasonal cycles in the near-background levels of stratospheric aerosol. The data analyzed were the extinction coefficient at 0.525 μ m ( β 0.525 ) and the extinction ratio at 0.525 μ m ( E 0.525 ) on the basis of climatological zonal monthly mean for the years 1998–2004. Distinct seasonal cycles were found for β 0.525 at 35–15°S above 28 km (region A) and at 20°S–30°N from 16 to 20.5 km (region B). In the A region, the seasonal cycle of E 0.525 was characterized by a maximum in local fall and can be explained by the ascent of mean meridional circulation in local summer and descent in local winter. In the B region, the seasonal cycles of E 0.525 were characterized by a maximum in October-January, which can be interpreted by meridional transport and mixing. The amplitude of the seasonal cycles for E 0.525 exhibited asymmetry between the Northern Hemisphere (NH) and the Southern Hemisphere (SH); the amplitudes at latitudes of 20–30° were larger in the SH than in the NH above 29 km, whereas they were larger in the NH than in the SH below 18 km. Comparison of the distribution of E 0.525 with that of SAGE II water vapor suggested that the E 0.525 distribution is controlled by the stratospheric circulation and troposphere-originated gases. One difference between E 0.525 and water vapor was found in the E 0.525 maximum that appears over the winter subtropics. The E 0.525 maximum can be attributed to the dominance of temperature and microphysical effects compared to transport effects, whereas the water vapor distribution can be attributed to transport effects. Another difference is that an upward propagation of the seasonal cycle of E 0.525 at 5°S–30°N disappeared near 23 km. This difference is explained by the fact that the chemical and microphysical processes of aerosol formation become significant above 23 km.

... Niwano et al ...

... This is in general agreement with the studies of Niwano et al ...

... and the ascent of the mean meridional circulation has a larger seasonal amplitude in the SH (Niwano et al ...

2006

3.982

0.0

. 2006, 33(12):null-null

Seasonal variability in the stratospheric aerosol layer in the current volcanically-quiescent period over two tropical stations in India using the twilight sounding method

B. Padma Kumari,A. L. Londhe,D. B. Jadhav andH. K. Trimbake

Indian Institute of Tropical Meteorology, Pune, India

> [1] The twilight photometry technique is used to study the variability of stratospheric aerosol layer over the tropical Indian inland stations, Pune (18.5°N, 73.9°E) and Karad (17.0°N, 74.2°E) during the volcanically quiescent period January 2000 to December 2003. The stratospheric aerosol loading is computed from the aerosol vertical profiles derived by twilight scattering technique. The time variation of monthly mean stratospheric aerosol loading shows small-scale variations in the background stratospheric aerosol loading with maximum loading in the winter.

2010

1.417

0.0

. 2010, 72:1024-1035 DOI:10.1016/j.jastp.2010.06.004

Latitudinal dependence of the seasonal variation of particulate extinction in the UTLS over the Indian longitude sector during volcanically quiescent period based on Lidar and SAGE-II observations

Abstract The altitude profiles of particulate extinction in the upper troposphere and lower stratosphere (UTLS) obtained from SAGE-II in the latitude region 0–30°N over the Indian longitude sector (70–90°E) are used to study the latitudinal variation of its annual pattern in this region during the volcanically quiescent period of 1998–2003. The SAGE-II data is compared with the lidar measurements from Gadanki (13.5°N, 79.2°E) when the satellite had an overhead occultation pass over a small geographical grid centered at this location. The particulate optical depth ( �� p ) in the UT region shows a general decrease with increase in latitude and a pronounced summer–winter contrast with relatively low values during winter and high values during summer. In general, these variations are in accordance with the latitudinal variation of convective available potential energy (CAPE) and thunderstorm activity, which are good representative indices of tropospheric convection. While the particulate extinction (and �� p ) in the 18–21 km (LS 1 ) region is relatively low in the equatorial region up to 15°N, it shows an increase in the off-equatorial region, beyond 15°N. While the annual variation of �� p in the LS 1 region is almost insignificant near the equator, it is rather well pronounced in latitude region between 10 and 15°N with relatively high values during winter and low values during summer. Beyond 20°N, this shows a prominent peak during summer. At a higher altitude, the 21–30 km (LS 2 ) region, the latitude variation of �� p shows a different pattern with high values near the equator and low values in the off-equatorial region confirming the existence of a stratospheric aerosol reservoir. Low values of �� p at lower regime (LS 1 ) near the equator could be due to rapid transport of particulates from the near equatorial region to higher latitudes, while the equatorial high at upper regime (LS 2 ) could be due to lofting and subsequent accumulation.

... Parameswaran et al ...

... S can be explained by the following two reasons: (1) Larger amounts of aerosols were brought up to the northern tropics upper troposphere by the Asian summer monsoon and other strong convective systems during boreal summer, causing the high aerosol concentrations in the upper troposphere region, as noted by Parameswaran et al ...

2010

0.0

2008

3.174

0.0

. 2008, 113(D10):null-null

Comparison of aerosol extinction coefficients, surface area density, and volume density from SAGE II and in situ aircraft measurements

J. M. Reeves 1 ,J. C. Wilson 1 ,C. A. Brock 2 andT. P. Bui 3

1 Department of Engineering, University of Denver, Denver, Colorado, USA 2 National Oceanic and Atmospheric Administration, Boulder, Colorado, USA 3 NASA Ames Research Center, Moffett Field, California, USA

> [1] Aerosol size distributions measured in the lower stratosphere by the University of Denver's focused cavity aerosol size spectrometer (FCAS) were used to calculate aerosol extinction coefficients, surface area densities, and volume densities for comparison with the Stratospheric Aerosol and Gas Experiment (SAGE) II version 6.20 data products. Profiles from ten high-altitude aircraft flights, ranging approximately 8.5 to 20.5 km altitude, are compared with nearby SAGE II occultation events. Nine of the flights date from late 1995 through 1997, and one is from early 2004. Extinctions are found to agree within instrumental uncertainties except at 386 nm below 17 km, where the SAGE II values are systematically low despite their large errors. Above 12 km, where the comparisons are statistically significant, the SAGE II volume density is about 35% lower than the FCAS measurements, though just within combined uncertainties, while the SAGE II surface area density is low compared to FCAS by a factor of 1.5 to 3. The limitations of principal component analysis may account for up to two thirds of the discrepancy in surface area density.

... Reeves et al ...

1995

3.174

0.0

. 1995, 100(D3):5173-5191

Seasonal cycle of the residual mean meridional circulation in the stratosphere

Karen H. Rosenlof

> The transformed Eulerian-mean (TEM) residual circulation is used to study the zonally averaged transport of mass in the stratosphere. The residual circulation is estimated from heating rates computed with a radiative transfer model using data from the Upper Atmosphere Research Satellite (UARS) as inputs. An annual cycle exists in the resulting circulation in the lower stratosphere, with a larger net upward mass flux across a pressure surface in the tropics during northern hemisphere winter than during northern hemisphere summer. The annual cycle in upward tropical mass flux follows the annual cycle in downward mass flux across a pressure surface in the northern hemisphere extratropics. It is argued that the annual cycle in zonal momentum forcing in the northern hemisphere stratosphere is controlling mass flux across a pressure surface in the lower stratosphere both in the tropics and in the northern hemisphere extratropics.

... The quantities studies by Rosenlof and Holton (1993) and Rosenlof (1995) revealed that the upward mass flux in the tropics across the 100 mb surface (about the height of the tropical tropopause) is much stronger in the northern winter than in the summer, and these processes normally lead to a wintertime maximum and summertime minimum in aerosol loading at the lower stratosphere levels ...

1993

3.174

0.0

. 1993, 98(D6):10465-10479

Estimates of the stratospheric residual circulation using the downward control principle

Karen H. RosenlofJames R. Holton

> The transformed Eulerian-mean momentum and continuity equations are used to calculate the residual mean meridional circulations for the lower stratosphere and troposphere. Momentum and temperature fluxes required for the computation are estimated from U.K. Meteorological Office (UKMO) analyzed geopotential heights. National Center for Atmospheric Research (NCAR) CCM2 model output is used to assess the errors associated with the calculation. The model comparisons showed that the method works reasonably well for solstice seasons, but is inadequate for equinox seasons. In addition, it is found that some parameterization of gravity wave drag needs to be included with the planetary wave forcing to accurately estimate the residual mean circulation using this method.

1989

3.174

0.0

. 1989, 94(D6):8335-8338

SAGE II aerosol data validation and initial data use: An introduction and overview

P. B. RussellM. P. McCormick

> Correlative sensors used in the SAGE II aerosol data validation program included two- and six-channel dustsondes; ground-based and airborne multiwavelength lidars; wire, ribbon, and related impactors; laser spectrometers; filter collectors; spectral polarimeters; and spectral limb cameras. Measurement campaigns were conducted in the northern, southern, eastern, and western hemispheres, and in low, middle, and high latitudes. Measurement conditions were often strongly perturbed by El Chichón and other volcanic eruptions, which posed new challenges because of (1) multimodal size distributions, (2) spatiotemporal inhomogeneity, and (3) large extinction values. New experimental and analytical approaches were developed to meet these challenges. Several of the analytical approaches use SAGE II four-wavelength aerosol extinction values to derive or check particle size distributions. Extensive comparisons between SAM II and SAGE II were also conducted. The validation results are detailed in the following six papers. They show that when correlative measurements are nearly coincident with the SAGE II measurements in space and time, the SAGE II and correlative values are consistent within their respective uncertainties. This is especially so of the SAGE II 1.02-μm extinction profiles, for which numerous instances of good coincidence show agreement from heights near the tropopause to ∼28 km. For the shorter wavelengths (0.525, 0.453, and 0.385 μm), several comparisons show agreement within mutual error bars at heights between ∼15 and 26 km. However, above ∼24 km, correlative observations are scarce and the data is of poorer quality because of low aerosol content and relatively strong Rayleigh, NO 2 , and ozone contributions. Thus for the short wavelengths, especially above ∼24 km, further correlative measurements would be desirable to provide a conclusive validation. Initial data use investigations demonstrate methods for inferring aerosol physical and optical properties from the SAGE II four-wavelength extinction data. The methods yield values and uncertainties for particle volume, area, effective size, distribution width, model size distribution parameters, number larger than specified sizes, and backscatter coefficient. In many cases, SAGE II-derived values are compared to measurements by dustsonde and lidar. Results vary, but they are usually consistent within mutual error bars.

... , Russell and McCormick, 1989 ...

2011

3.174

0.0

. 2011, 116(D13):null-null

Variability in background stratospheric aerosols over the tropics and its association with atmospheric dynamics

S. V. Sunilkumar,K. Parameswaran,Bijoy V. Thampi andGeetha Ramkumar

Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum, India

> [1] Spatiotemporal variability of background stratospheric aerosols over the tropics (30°S–30°N) and its association with atmospheric dynamics are studied using the zonal-averaged Stratospheric Aerosol and Gas Experiment II (SAGE-II) derived aerosol extinction at 525 nm along with lidar data at 532 nm from Gadanki (13.5°N, 79.2°E) during the period 1998–2005. In general, a pronounced increase in aerosol loading is observed in the spatial distribution of aerosols over the equatorial region compared to the off-equatorial regions. The particulate optical depth ( τ P ) in the lower stratospheric region showed an increasing trend particularly after 2002 in both these regions. This increase could partly be attributed to a corresponding increase in the number of feeble/minor volcanic eruptions. Over and above this steady increase, the τ P also showed significant periodic variations. In addition to the prominent short-period variations, the stratospheric τ P showed a significant biennial variation (with a period of ∼30 months) in association with stratospheric quasi-biennial oscillation in zonal wind (QBO U ). During the westerly phase of stratospheric QBO U , the mean particulate optical depth decreases rapidly with increase in latitude on either side of equator in both the hemispheres, while it remains fairly steady around the equator up to 15° in latitude on either side with a small bite-out around the equator during the easterly phase, particularly during the very quiet period of 1998–2002. During the latter half (after 2002), when the stratosphere was mildly disturbed, the latitudinal variation of τ P was fairly similar in both phases of QBO U with a higher value of τ P near the equator during the westerly phase. The QBO signal in aerosol extinction around 25 km is found to be in opposite phase with that observed in the upper regime (28–32 km) and lower regime (18–22 km), depicting the influence of the secondary meridional circulation produced owing to vertical shear of QBO U in the equatorial region.

... Sunilkumar et al ...

2008

5.51

0.0

... Since the late 1990s, stratospheric aerosols have been characterized by relatively steady levels because of the lack of major volcanic eruptions after the Pinatubo eruption in June 1991 (Thomason et al ...

... The sensitivity study by Thomason et al ...

2004

0.0

... Wang et al ...

2001

0.0

... Wu et al ...

2012

0.0

. 2012, 5(2):95-101

An empirical method for estimating background stratospheric aerosol extinction profiles over China

Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

The current paper introduces an empirical method for estimating the vertical distribution of background stratospheric aerosol extinction profiles covering the latitude bands of 50��5��N, 40��5��N, 30��5��N, and 20��5��N and the longitude range of 75-135��E based on Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction measurements at wavelengths of 1020 nm, 525 nm, 452 nm, and 386 nm for the volcanically calm years between 1998-2004. With this method, the vertical distribution of stratospheric aerosol extinction coefficients can be estimated according to latitude and wavelength. Comparisons of the empirically calculated aerosol extinction profiles and the SAGE II aerosol measurements show that the empirically calculated aerosol extinction coefficients are consistent with SAGE II values, with relative differences within 10% from 2 km above the tropopause to 33 km, and within 22% from 33 km to 35 km. The empirically calculated aerosol stratospheric optical depths (vertically integrated aerosol extinction coefficient) at the four wavelengths are also consistent with the corresponding SAGE II optical depth measurements, with differences within 2.2% in the altitude range from 2 km above the tropopause to 35 km.

... Yang, 2012) ...