Climatology of Upper-Tropospheric Relative Humidity from the Atmospheric Infrared Sounder and Implications for Climate

• Published in: Journal of climate Vol. 19; no. 23; pp. 6104 - 6121
• Main Authors: Gettelman, Andrew, Collins, William D., Fetzer, Eric J., Eldering, Annmarie, Irion, Fredrick W., Duffy, Phillip B., Bala, Govindasamy
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01-12-2006
• Subjects: Asian monsoons; Atmosphere; Atmospheric circulation; Atmospheric Infrared Sounder; Climate; Climate change; Climate models; Climatology; Clouds; Design specifications; Diagnostic tests; Earth, ocean, space; Exact sciences and technology; External geophysics; General circulation models; High humidity; Humidity; Ice; Lower troposphere; Meteorology; Middle troposphere; Missing data; Monsoon circulation; Monsoons; Ozone; Radiation; Relative humidity; Satellite observation; Satellite systems; Storms; Stratosphere; Subtropics; Temperate regions; Temperature; Tropical climates; Tropical environments; Tropical regions; Tropopause; Troposphere; Tropospheric humidity; Upper troposphere; Variability; Vertical profiles; Walker circulation; Water in the atmosphere (humidity, clouds, evaporation, precipitation); Water vapor; Relative humidity; Microwave scanner; Infrared scanner; Climatology; time variations; Satellite observation; Climate models; digital simulation; Atmospheric sounding; troposphere; Polar orbiting satellite; water vapor; Vertical profile; Tropopause; Planetary scale; spatial variations; Aqua satellite; atmospheric circulation; Atmospheric humidity; high resolution
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI3956.1

Recently available satellite observations from the Atmospheric Infrared Sounder (AIRS) are used to calculate relative humidity in the troposphere. The observations illustrate many scales of variability in the atmosphere from the seasonal overturning Hadley–Walker circulation to high-frequency transient variability associated with baroclinic storms with high vertical resolution. The Asian monsoon circulation has a strong impact on upper-tropospheric humidity, with large humidity gradients to the west of the monsoon. The vertical structure of humidity is generally bimodal, with high humidity in the upper and lower troposphere, and a dry middle troposphere. The highest variances in humidity are seen around the midlatitude tropopause. AIRS data are compared to a simulation from a state-of-the-art climate model. The model does a good job of reproducing the mean humidity distribution but is slightly moister than the observations in the middle and upper troposphere. The model has difficultly reproducing many scales of observed variability, particularly in the Tropics. Differences in humidity imply global differences in the top of atmosphere fluxes of ~1 W m-2.