Atmos. Chem. Phys. Discuss., 12, 27521-27554, 2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Improved SAGE II cloud/aerosol categorization and observations of the asian tropopause aerosol layer: 1989–2005
L. W. Thomason1 and J.-P. Vernier2
1NASA Langley Research Center, Hampton, Virginia, USA
2Science Systems and Applications, Inc., Hampton, Virginia, USA

Abstract. Observations by CALIPSO have recently been used to identify an aerosol enhancement associated with the Asian Monsoon anticyclone. The Asian Tropopause Aerosol Layer (ATAL) is analogous to observed enhancements in long-lived trace gas species like CO. Since the CALIPSO record only begins in 2006, the question of how long this aerosol feature has been present requires a new look at the long-lived SAGE II data sets despite significant hurdles to its use in the subtropical upper troposphere. We found that a new and more robust method for identifying and eliminating cloud effects from the SAGE II data set was required and, herein, we describe a cloud identification method that appears to capture cloud/aerosol events more effectively than early methods. In addition, we summarize additional challenges to observing the ATAL layer using SAGE II observations. Finally, we perform analyses of the upper troposphere, focusing on periods in which the UTLS is relatively free of volcanic material (1989–1990 and after 1996). We find that there is no evidence of ATAL in the SAGE II data prior to 1998. After 1998, it is clear that aerosol in the upper troposphere in the ATAL region is substantially enhanced relative to the period before that time. In addition, the data generally supports the presence of the ATAL layer beginning in 1999 and continuing through the end of the mission though some years (e.g. 2003) are complicated by the presence of episodic enhancements most likely of volcanic origin.

Citation: Thomason, L. W. and Vernier, J.-P.: Improved SAGE II cloud/aerosol categorization and observations of the asian tropopause aerosol layer: 1989–2005, Atmos. Chem. Phys. Discuss., 12, 27521-27554, doi:10.5194/acpd-12-27521-2012, 2012.
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