Tropospheric Water Vapor Anomalies During the 2006-07 and 2009-10 El Niños

The water vapor measurements from the Aura Microwave Limb Sounder (MLS, above 300 hPa) and Aqua Atmospheric Infrared Sounder (AIRS, below 300 hPa) are analyzed to study the variations of water vapor during the 2006-7 and 2009-10 El Niños. The 2006-7 El Niño is a canonical East Pacific (EP) El Niño, while the 2009-10 El Niño is a new type of El Niño known as Central Pacific (CP) El Niño or El Niño Modoki. Results show that these two types of El Niño events produce different patterns of water vapor anomalies over the tropical ocean, which approximately resemble those of cloud anomalies shown in Su and Jiang [2012]. Moreover, the regression of water vapor anomalies onto the Niño-3.4 SST for the A-Train period is conducted and a clear “upper tropospheric amplification” of the fractional water vapor change to El Niño is found. Finally, GFDL model simulations of water vapor and clouds were examined and compared with the satellite observations. The model simulates the 2009-10 El Niño better than the 2006-07 El Niño, and its simulations of clouds and relative humidity in the middle troposphere (~600 hPa) are particularly poor.