HR: 0800h
AN: A51B-0765    [Abstracts]
TI: Nighttime cirrus detection in the AIRS/AMSU suite: Global application and comparison to cirrus climatologies
AU: * Kahn, B H
EM: briank@atmos.ucla.edu
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 United States
AU: * Kahn, B H
EM: briank@atmos.ucla.edu
AF: UCLA Department of Atmospheric and Oceanic Sciences, 405 Hilgard Avenue Box 951565, Los Angeles, CA 90095-1565 United States
AU: Liou, K
EM: knliou@atmos.ucla.edu
AF: UCLA Department of Atmospheric and Oceanic Sciences, 405 Hilgard Avenue Box 951565, Los Angeles, CA 90095-1565 United States
AU: Eldering, A
EM: annmarie.eldering@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 United States
AU: Eldering, A
EM: annmarie.eldering@jpl.nasa.gov
AF: UCLA Department of Atmospheric and Oceanic Sciences, 405 Hilgard Avenue Box 951565, Los Angeles, CA 90095-1565 United States
AU: Braverman, A
EM: amy.braverman@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 United States
AB: We use the Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit A (AMSU-A) instrument suite onboard EOS-Aqua for the detection of cirrus clouds at nighttime. The proposed technique utilizes carefully selected infrared (IR) window channels near 3.8 and 10.4 microns and total column precipitable water (PW) measurements, derived from the synergistic AIRS and AMSU-A water vapor retrievals. We constrain the brightness temperature difference (dBT) using the PW measurements in order to determine if cirrus clouds are present. Simulated dBTs initialized with radiosonde profiles of temperature and humidity are used to define the boundaries between "cloudy sky" and "uncertain sky" categories, which contain both cloudy and clear footprints. Considerations of the impact of IR channel noise, surface emissivity, skin and air temperature differences, temperature and relative humidity profile variations, and instrument view angle are made. Simulations of cirrus clouds indicate this technique detects most all cirrus with tau(IR) greater than 0.1 over the tropical and subtropical oceans, and some (but not all) of the cirrus with tau(IR) less than 0.1. An analysis of coincident observations using Atmospheric Radiation Measurement (ARM) Tropical Western Pacific (TWP) site cloud boundaries and the proposed technique applied to the AIRS/AMSU suite indicates agreement for 82-84 percent of the cases. Most of the disagreements are explained well by AIRS footprint-scale heterogeneity compared to ARM point measurements, possible mixed phase microphysics in midlevel clouds, and significant IR channel noise for cold BT scenes over deep convective towers. We develop climatological maps of detected cirrus for select periods of time over the tropical and subtropical oceanic regions of the world, and make comparisons to other cirrus cloud climatologies. Discussion and analysis of the results will emphasize the frequency of occurrence of cirrus clouds.
DE: 3359 Radiative processes
DE: 3360 Remote sensing
DE: 3374 Tropical meteorology
DE: 1640 Remote sensing
DE: 0305 Aerosols and particles (0345, 4801)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting