Climate Variability of Extreme Weather Events Observed by the Atmospheric Infrared Sounder (AIRS)

Monitoring the intensity and frequency of extreme weather events and identifying their changes in a warming global climate become urgent tasks in both climate research and management of the associated risks and adaptation. Using directly measured radiances from space-borne instruments to gauge extreme weather events has the advantage of complete global coverage, while avoiding the biases or errors from complex retrieval methods. The stable and accurately calibrated Atmospheric Infrared Sounder Level 1B (AIRS L1B) radiance data allow detecting global extreme weather events and provide a long-term record of such events for climate studies. We have utilized AIRS radiances from the window-channel 1231 cm-1 (8.1 µm) to detect extreme cloud top temperatures. The brightness temperatures of the window channel (BT1231) directly measure cloud top temperatures, and the cold ends of its probability density functions (PDFs) identify extremely cold cloud tops. First, we demonstrate examples of extreme events that were detected by AIRS BT1231. Second, we perform statistical analysis to show that the averaged BT1231 at the cold ends of the PDFs over the tropical ocean are negatively scaled with the tropically averaged Sea Surface Temperature (SST), with the lower quantiles being significantly more susceptible to changes in SST. The regions of high sensitivity of BT1231 to changes in SST are located by the edges of Inter-Tropical Convergence Zone, where monsoons and tropical cyclones frequently occur, and are associated with transition from shallow to deep convections.