Five year (2004–2009) observations of upper tropospheric water vapor and cloud ice from MLS and comparisons with GEOS-5 analyses

Abstract

This paper gives an overview of August 2004 through February 2010 upper tropospheric (UT) water vapor (H₂O) and ice water content (IWC) from the Aura Microwave Limb Sounder (MLS) and comparisons with outputs from the NASA Goddard Earth Observing System Version 5 (GEOS-5) data assimilation system. Both MLS and GEOS-5 show that high values of H₂O and IWC at 215 to 147 hPa are associated with areas of deep convection. They exhibit good (within ∼15%) agreement in IWC at these altitudes, but GEOS-5 H₂O is ∼50% (215 hPa) to ∼30% (147 hPa) larger than MLS values, possibly due to higher temperatures in the data assimilation system at these altitudes. A seasonally migrating band of tropical deep convection is clearly evident in both the MLS and GEOS-5 UT H₂O and IWC, but GEOS-5 produces a weaker intertropical convergence zone than MLS. MLS and GEOS-5 both show spatial anticorrelation between IWC and H₂O at 100 hPa, where low H₂O is associated with low temperatures in regions of tropical convection. At 100 hPa, GEOS-5 produces 50% less IWC and 15% less H₂O in the tropics, and ∼20% more H₂O in the extratropics, than does MLS. Behavior of the 100 hPa H₂O is consistent with it being controlled by temperature. The seasonal cycle in the vertical transport of tropical mean H₂O from ∼147 hPa to ∼10 hPa appears much stronger in MLS than in GEOS-5. The UT IWC and H₂O interannual variations, from both MLS and GEOS-5, show clear imprints of the El Niño–Southern Oscillation.