Abstract
We have utilized Solar Backscatter Ultraviolet (SBUV) instrument measurements of atmospheric radiance to create a 40-year record of polar mesospheric cloud (PMC) behavior. While this series of measurements is nearing its end, we show in this paper that Ozone Mapping and Profiling Suite (OMPS) Nadir Profiler (NP) instruments can be added to the merged SBUV PMC data record. Regression analysis of this extended record shows smaller trends in PMC ice water content (IWC) since approximately 1998, consistent with previous work. Current trends are significant at the 95% confidence level in the Northern Hemisphere, but not in the Southern Hemisphere. The PMC IWC response to solar activity has decreased in the Northern Hemisphere since 1998, but has apparently increased in the Southern Hemisphere.
Highlights
Determination of long-term variations in the Earth’s mesosphere (60–100 km) is challenging
We find that separating this data set into two sections, with a break point selected in 1998, provides an effective characterization of polar mesospheric cloud (PMC) behavior throughout this long data record
Stevens et al (2017) calculated daily average ice water content (IWC) during July 2009 as a function of latitude, using output from the NOGAPS-ALPHA forecast-assimilation system and the Hervig et al (2009) 0-D model to create IWC values from these data. When they apply a threshold of IWC > 40 g km−2, their zonal average results are approximately 20 %–30 % greater than the NOAA-19 Solar Backscatter Ultraviolet (SBUV)/2 seasonal average values for Northern Hemisphere (NH) 2009 shown in Figs. 4b, 5b, and 6b. Possible causes for this difference include the use of Julyonly averages compared to the longer season defined in this paper, the averaging of model results at all local times compared to the specific local time of the measurements, and the different methods used to create IWC values
Summary
Determination of long-term (multi-decadal) variations in the Earth’s mesosphere (60–100 km) is challenging. Since the lifetime of a single instrument is generally limited to 10–15 years, maintaining continuity for a specific parameter over multiple decades again becomes an issue Another option is to measure an observable quantity that provides indirect information about the background state of the mesosphere.
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