Observed Interannual Variability of Tropical Troposphere Relative Humidity

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Abstract
Relative humidity fields from the High-Resolution Infrared Radiation Sounder (HIRS) flown on NOAA series satellites since 1979 have been used to study the seasonal aspects of the interannual variability of relative humidity in the tropical troposphere. The El Niño–Southern Oscillation (ENSO) is the only statistically identifiable physical mechanism of such variability. Boreal winter (December–February) relative humidity variations during an ENSO event follow patterns of anomalous convection and large-scale upper-level circulation. During El Niño (La Niña) regions of large negative (positive) relative humidity anomalies exist at subtropical latitudes over the Pacific Ocean. These are not always balanced by increases (decreases) in humidity near the equator. NCEP– NCAR reanalysis temperatures are used to separate observed changes in relative humidity into contributions from tropospheric temperature versus the contribution from changes in water vapor content. The authors find that at subtropical lat... Abstract Relative humidity fields from the High-Resolution Infrared Radiation Sounder (HIRS) flown on NOAA series satellites since 1979 have been used to study the seasonal aspects of the interannual variability of relative humidity in the tropical troposphere. The El Niño–Southern Oscillation (ENSO) is the only statistically identifiable physical mechanism of such variability. Boreal winter (December–February) relative humidity variations during an ENSO event follow patterns of anomalous convection and large-scale upper-level circulation. During El Niño (La Niña) regions of large negative (positive) relative humidity anomalies exist at subtropical latitudes over the Pacific Ocean. These are not always balanced by increases (decreases) in humidity near the equator. NCEP– NCAR reanalysis temperatures are used to separate observed changes in relative humidity into contributions from tropospheric temperature versus the contribution from changes in water vapor content. The authors find that at subtropical lat...

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