High, Tropical Cirrus Clouds as Indicators of the Tropical Belt Extent and Changes
Tuesday, July 28, 2015: 11:20 AM
Melody A Avery1, Mark R Schoeberl2, Mark A. Vaughan1, Eric J Jensen3, Charles R Trepte1, Jayanta Kar4, Yongxiang Hu1, Stuart A Young5, Troy D Thornberry6 and Andrew W Rollins7, (1)NASA Langley Research Center, Hampton, VA, United States, (2)Science and Technology Corporation, Boulder, CO, United States, (3)NASA Ames Research Center, Moffett Field, CA, United States, (4)Science Systems and Applications, Inc. Hampton, Hampton, VA, United States, (5)CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia, (6)NOAA ESRL, Boulder, CO, United States, (7)NOAA Boulder, Boulder, CO, United States
Abstract:
Recent climate model predictions, satellite data and meteorological reanalysis data sets suggest that not only is the width of the tropical belt increasing, but the amount and location of the highest tropical cirrus clouds is changing as well. The focus of the research presented here is to characterize changes in the tropical upper troposphere, using measurements of thin cirrus clouds. The Cloud and Aerosol LIdar with Orthogonal Polarization (CALIOP) on the CALIPSO satellite has captured what will soon be nine years of measurements of elastic backscatter (at 532 and 1064 nm) and depolarization (at 532 nm). CALIOP measures backscatter and depolarization from TTL cirrus of all particle sizes, until the laser light is completely attenuated at an optical depth of about 3, enabling the lidar to detect very thin TTL cirrus clouds. Zonal mean CALIOP measurements of TTL cirrus occurrence frequency have been used previously as indicators of TTL width and height. However, in addition to the extended data record, there are several factors that cause this analysis to be more accurate and more comprehensive than earlier studies. A critical factor is the increased stability of the recent Version 4 CALIOP calibration, due to a higher stratospheric reference altitude that is not impacted significantly by volcanic aerosols. We also take advantage of the recent Airborne Tropical TRopopause EXperiment (ATTREX) aircraft measurements of condensed (ice) water in the TTL to evaluate our thin cirrus extinction retrievals and cirrus ice water parameterization. Using the ATTREX in situ measured ice water content information and nine years of CALIOP Version 4 Level 1 backscatter and depolarization data, we develop an extended 3-dimensional monthly mean TTL ice water content data set used to track changes in the size and shape of the TTL from June 2006 - June 2015, and to correlate variations in TTL ice water content with the ENSO, QBO and other climate cycles.
