How much ice is there in the Tropical Tropopause Layer? Observations from the ATTREX mission, from the Global Hawk and from Space

Thursday, 18 December 2014: 10:50 AM
Melody A Avery1, Troy D Thornberry2, Stuart A Young3, Sarah Woods4, Qixu Mo4, Paul Lawson4, Matthew J McGill5, Mark Vaughan6, John E Yorks7, Jacques Robert Pelon8, Glenn S Diskin9, Eric J Jensen10, Dennis L Hlavka7, David M Winker11, David W Fahey12, Charles R Trepte11, Bruce Gandrud4, Anne Garnier13 and Andrew W Rollins2, (1)NASA Langley Research Ctr, Hampton, VA, United States, (2)NOAA ESRL, Boulder, CO, United States, (3)CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia, (4)SPEC Inc, Boulder, CO, United States, (5)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (6)NASA, Hampton, VA, United States, (7)SSAI/NASA GSFC, Greenbelt, MD, United States, (8)CNRS, Paris, France, (9)NASA Langley Research Ctr, Hampton, VA, United States, (10)NASA Ames Research Center, Moffett Field, CA, United States, (11)NASA Langley Research Center, Hampton, VA, United States, (12)University of Colorado / CIRES, Boulder, CO, United States, (13)Science Systems and Applications, Inc. Hampton, Hampton, VA, United States
The Airborne Tropical TRopopause EXperiment (ATTREX) aims to quantify the impact of the slow ascent of tropospheric air through the Tropical Tropopause Layer (TTL) on the water vapor content of the stratosphere, including better understanding of the relationship between TTL ice and water vapor. In situ and remote sampling of very high-altitude clouds in the coldest part of the tropopause from the Global Hawk provides a set of unique microphysical data to combine with regional Cloud Aerosol LIdar with Orthogonal Polarization (CALIOP) and Imaging Infrared Radiometer (IIR) observations from the CALIPSO satellite. The goal here is to upscale bulk cloud properties derived from the measured microphysical data to regional statistics of TTL sub-visible cirrus cloud extinctions and ice water content (IWC). If this can be credibly done then one can take advantage of 8 years of CALIPSO observations to characterize inter-annual variability and to study the impact of changes in the total water budget of the TTL on lower stratospheric composition and ultimately, on climate.

Before ATTREX, very few cold TTL cloud microphysical data sets were available. NASA’s ATTREX EV-1 mission used Global Hawk (GH) to sample between about 14 – 18 km in the Tropical Northern Hemispheric (NH) Eastern Pacific in Jan/Feb 2013, and Western Pacific in Jan/Feb 2014. The GH flew with a suite of modern, fast-response optical cloud probes (Hawkeye) and a particle imager (CPI), a "total water" instrument (NOAA), a diode laser hygrometer (DLH), and the Cloud Physics Lidar (CPL). In this presentation we use the geometric optics approximation to relate the measured ice particle projected area from Hawkeye to the extinction coefficients retrieved by CPL and CALIOP from attenuated backscatter. Where we have coincidences, we compare the CALIOP Version 3 and newer temperature-dependent IWC parameterizations with the NOAA total water and DLH measurements, to evaluate the accuracy of the CALIOP area to mass conversion for cold, TTL clouds. We also compare the measured size distributions from Hawkeye with the IIR microphysical parameter and effective diameter for TTL single layer high altitude cirrus clouds. Informed by these comparisons, we give an overview of the regional characteristics of TTL sub-visible cirrus cloud layers in the NH Western Pacific.