A32C-05
Recent Divergences Between Stratospheric Water Vapor Measurements by Aura MLS and Frost Point Hygrometers

Wednesday, 16 December 2015: 11:20
3012 (Moscone West)
Dale F Hurst1, Karen Hepler Rosenlof2, Sean M Davis1,2, Emrys G Hall1,3, Allen F Jordan1,3, William G Read4, Holger Voemel5 and Henry B Selkirk6,7, (1)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (2)Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, United States, (3)Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, CO, United States, (4)JPL / Caltech, Pasadena, CA, United States, (5)Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, CO, United States, (6)GESTAR, Universities Space Research Association, Columbia, MD, United States, (7)NASA Goddard Space Flight Center, Laboratory for Atmospheric Chemistry and Dynamics, Greenbelt, MD, United States
Abstract:
A recent comparison of stratospheric water vapor measurements by the Aura Microwave Limb Sounder (MLS) and frost point hygrometers (FPs) during 2004-2012 reported agreement better than 1% from 68 to 26 hPa, small but statistically significant biases at 83 and 100 hPa, and no compelling evidence of long-term linear trends in FP–MLS differences [Hurst et al., 2014]. A previous comparison [Voemel et al., 2007] also found good agreement above 83 hPa. Recently it has become evident that differences between FP and MLS stratospheric water vapor measurements have widened during the last 5 years at two Northern Hemisphere (NH) mid-latitude sounding sites.

Here we examine differences between coincident MLS and FP measurements of stratospheric water vapor at five sounding sites: two in the NH mid-latitudes (Boulder, Colorado and Lindenberg, Germany), two in the tropics (San Jose, Costa Rica and Hilo, Hawaii), and one in the SH mid-latitudes (Lauder, New Zealand). Analyses of the Boulder and Lindenberg data reveal reasonably uniform breakpoints in the timeseries of FP–MLS differences throughout the stratosphere, indicating that trends after mid-2010 are statistically different from trends before mid-2010. At Boulder and Lindenberg the post-breakpoint trends are statistically significant and fairly consistent over eight MLS retrieval pressures (100-26 hPa), averaging –0.08 ± 0.02 and –0.05 ± 0.02 ppmv per year, respectively (Figure 1). These translate to mean changes in stratospheric FP–MLS differences of –0.42 ± 0.08 ppmv (–10 ± 2%) and –0.23 ± 0.08 ppmv (–6 ± 2%) between mid-2010 and mid-2015. Breakpoints for the eight MLS pressure levels above Lauder are less uniform than for the two NH sites, however forced breakpoints of mid-2010 produce a mean stratospheric trend of –0.05 ± 0.02 ppmv per year in the FP–MLS differences. Breakpoints for the two tropical sites are inconsistent, as are the trend results with forced breakpoints of mid-2010.

Hurst, D.F., et al., (2014), J. Geophys. Res. Atmos., 119, doi:10.1002/2013JD020757.

Voemel, H., et al. (2007), J. Geophys. Res., 112, doi:10.1029/2007JD008698.

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