Sun Wong

Texas A&M

Dust Heating in the Lower Troposphere and its Long-Term Implications

Room 811 AO&SS, December 2, 2008, 12:00 PM

Abstract

The role of Saharan dust and dry anomaly in heating up the Saharan Air Layer (SAL) is investigated. The dust aerosol optical thickness (AOT) in the SAL is inferred from the measurements taken by Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), and the corresponding temperature and specific humidity anomalies are identified using the NCEP data in August-September over the North Atlantic tropical cyclone (TC) main development region (MDR). We find that higher AOT is associated with warmer and dryer anomalies below 700 hPa. The calculated instantaneous radiative heating anomalies from a radiative transfer model indicate that both the dust and low humidity are essential in maintaining the temperature structure in the SAL against thermal relaxation. At 850 hPa, heating anomalies caused by both the dust and dry anomalies (for AOT > 0.8) are 0.4-0.7 K/day. The dust heats the atmosphere below 600 hPa, while the dry anomaly cools the atmosphere below 925 hPa, resulting in a peak of heating rate anomaly located at 700-850 hPa. Given the importance of Saharan dust heating up the lower troposphere, we further investigate its long-term transport variability and find that a decreasing trend of the loading of Saharan dust over the MDR is linked to the warming of the North Atlantic.