Polar Ozone and Aerosol Measurement III measurements of water vapor in the upper troposphere and lowermost stratosphere

Abstract

[1] We present water vapor measurements made by the Polar Ozone and Aerosol Measurement (POAM) III instrument since May 1998 in the upper troposphere and lowermost stratosphere. While POAM III is primarily a stratospheric instrument, many of the POAM III occultation measurements allow for the retrieval of water vapor in the upper troposphere. The Measurements of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) instruments provide a large number of coincident measurements and thus offer the best opportunity to validate POAM measurements in the highly spatially variable regions of the upper troposphere-lowermost stratosphere, where the mixing ratios are much larger than those found throughout most of the stratosphere. The comparison shows that there is no statistically significant difference in the response of the two instruments to changes in water vapor and that in the regime where the MOZAIC measurements are thought to be most accurate, the water vapor mixing ratios measured by POAM are 10% higher. The POAM III Northern Hemisphere measurements are taken from 55°to 71°and show a qualitatively reasonable seasonal variation, with high mixing ratios in the upper troposphere in the summer and low mixing ratios in the winter. Comparisons of the seasonal variations of the POAM measurements with those from the upper tropospheric Microwave Limb Sounder (MLS) measurements from the early 1990s show qualitative similarities. The $1 km vertical resolution of POAM measurements allows us to study in greater detail than other satellite instruments the complex variations in water vapor that occur in the upper troposphere and lowermost stratosphere. Among the interesting features observed is a rise in the level of the highlatitude hygropause from April through September.

Technical Note: Reanalysis of upper troposphere humidity data from the MOZAIC programme for the period 1994 to 2009

“…Studies by Crowther et al (2002), Offermann et al (2002), and Spichtinger et al (2004) analysed MOZAIC UTH data from the period 1995-1999, whereas Nedoluha et al (2002) and Kley et al (2007) Fig. 5b in .…”

“…The distribution of UTH was investigated in tropical (Bortz et al, 2006;Kley et al, 2007;Luo et al, , 2008Sahu et al, 2009Sahu et al, , 2011 and polar (Nedoluha et al, 2002) regions. MOZAIC RH data were also used for the validation of satellite instruments (e.g.…”

Upper tropospheric water vapour variability at high latitudes – Part 1: Influence of the annular modes

“…The amplitude is calculated by taking the ratio of climatological monthly means at maximum (January or December) and minimum (August or September). Note that POAM III has a different orbit that tends to sample consistently at higher latitudes (Nedoluha et al, 2002) and thus tends to have stronger seasonality at 8 km (driven by the larger temperature range). The saturation vapour pressure climatology is obtained using GEM analysis temperatures sampled at ACE measurement locations.…”

“…POAM III has been validated down to 8 km or ∼ 300 mb (Nedoluha et al, 2002;Lumpe et al, 2006), and this is used as the POAM III lower altitude limit in this work. Previous comparisons between MAESTRO and ACE-FTS have been favourable (Sioris et al, 2010;Carleer et al, 2008).…”

“…The same process is followed to generate anomalies of temperature, relative humidity (RH), tropopause pressure, and tropopause height. The anomalies of relative humidity with respect to ice are based on pressure and temperature from the GEM assimilation system and an accurate saturation vapour pressure formulation (Murray, 1967). The latitude sampling anomaly is generated by calculating the monthly average of sampled latitudes for each high-latitude band and then the mission-averaged latitude in each highlatitude band is subtracted.…”