ATMOS version 3 water vapor measurements: Comparisons with observations from two ER‐2 Lyman‐α hygrometers, MkIV, HALOE, SAGE II, MAS, and MLS

Abstract

[1] We have compared a new version of Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) retrievals (version 3) of stratospheric and mesospheric water vapor with observations from shuttleborne, satelliteborne, balloonborne, and aircraftborne instruments. These retrievals show agreement to within 5% with the MkIV observations in the middle and lower stratosphere. ATMOS agrees with the National Oceanic and Atmospheric Administration (NOAA) Lyman-a hygrometer to within 5% except for features with spatial scales less than the vertical resolution of ATMOS (such as the lower stratospheric seasonal cycle). ATMOS observations are 10 -16% lower than measurements from the Harvard Lyman-a hygrometer in the lower stratosphere and are 7 -14% higher than those from the Microwave Limb Sounder (MLS; prototype version 0104) throughout most of the stratosphere. Agreement is within 7% with the Millimeter-Wave Atmospheric Sounder (MAS; version 20) in the middle and upper stratosphere, but differences are closer to 13% in the lower stratosphere. Throughout the stratosphere, agreement is within 8% with the Halogen Occultation Experiment (HALOE; version 19). ATMOS data from 1994 show agreement with the Stratospheric Aerosol and Gas Experiment II (SAGE II; version 6) values to within 8% in the middle stratosphere, but ATMOS observations are systematically higher than those from SAGE II by as much as 41% in the lower stratosphere. In contrast, ATMOS 1985 values are systematically $50% lower than SAGE II values from sunset occultations in the lower stratosphere near 70 hPa but appear to be in better agreement with sunrise occultations. Version 3 retrievals in the upper stratosphere and lower mesosphere are typically 5 -10% lower than version 2 values between 1 and 0.05 hPa. This reduction improves agreement with HALOE, MAS, and MLS upper atmospheric observations, but ATMOS values still tend to be higher than values from these instruments in the middle mesosphere. Agreement among the instruments compared here (except for SAGE II) is generally within 15% in the middle to lower stratosphere and mesosphere and within 10% in the middle to upper stratosphere. At altitudes near 30 km, all instruments (including SAGE II) agree to within 10%.

Comparison of Stratospheric Aerosol and Gas Experiment (SAGE) II version 6.2 water vapor with balloon‐borne and space‐based instruments

“…Since both SAGE II and HALOE are carried on inclined-orbit satellites, occultation events are globally distributed. Comparison was divided into 3 periods: 1991-1992, June 1993to April 1994, and 1995-2003, so as to understand SAGE II performance in dealing with different problematic periods, mainly volcanic eruptions and short events.…”

“…Over the years, several versions of SAGE II water vapor have been released and validated, most recently version 6.0 and 6.1 in 2000 and 2001. Various reviews of these versions indicated a consistent dry bias around the hygropause by as much as $40% [Chiou et al, 2000;Michelson et al, 2002;Kanzawa et al, 2002]. The retrieval is also strongly affected by volcanic aerosol contamination following El Chichón (1982) and Pinatubo (1991) and to a lesser extent, Ruiz (1985) and Kelut (1990) [Rosenlof et al, 2001;Kley et al, 2000].…”

Atmospheric Trace Molecule Spectroscopy (ATMOS) Experiment Version 3 data retrievals

“…38 However, as discussed in Ref. 24 and illustrated in Fig. 15, a comparison of Version 2 and 3 results shows lower VMR for stratospheric water in this region for Version 3, while the VMRs for CH 4 are effectively unchanged.…”

“…For illustrative purposes, profiles are compared from different spectral filters, but these were observed in similar air masses ͑as measured by potential temperature and a scaled potential vorticity; see Ref. 24 or 28͒. Version 3 profiles, both in Fig. 14 and in general, avoid the unrealistically low neartropopause H 2 O mixing ratios often seen in Version 2.…”

“…There is better internal consistency as well as an improved agreement with the Halogen Occultation Experiment ͑HALOE͒, Millimeter-wave Atmospheric Sounder (MAS), and Microwave Limb Sounder (MLS). 24 The only significant stratospheric reservoirs for hydrogen are H 2 O, CH 4 , and H 2 . Oxidations of CH 4 and H 2 are the only significant local sources of H 2 O, so changes in the sum ͓H 2 O͔ ϩ 2͓CH 4 ͔ are indicative of changes in H 2 ͑where ͓͔ is the VMR͒.…”