Analysis of northern midlatitude noctilucent cloud occurrences using satellite data and modeling

Abstract

Motivated by numerous ground-based noctilucent cloud (NLC) sightings at latitudes as low as 40°N in recent years, we have conducted a study to determine if there have been any systematic NLC increases in the midnorthern latitudes. This question is addressed through investigating both the measured and modeled polar mesospheric cloud (PMC) occurrence frequencies. Temperature measured by the SABER instrument on the TIMED satellite over the 2002-2011 time period and a 7 year water vapor climatology developed from the data measured by the MLS instrument on the Aura satellite for the 2005-2011 period are used to simulate midlatitude PMCs. PMCs measured by the OSIRIS instrument on the Odin satellite and the SHIMMER instrument on the STPSat-1 satellite are used to extensively validate the model-generated PMC results. After validating the model against the PMC data, the model results were used to examine changes in the PMCs at midlatitudes between 2002 and 2011. The results show a statistically significant increase in the number of PMCs each season in the latitude range 40°N-55°N for the 10 year period examined. Increases in cloud frequency appear to be driven by the corresponding temperature decreases over the same time period. During this time, solar activity decreased from an active to a quiet period, which might have been partially responsible for the temperature decrease over this time period.

Updated PMC trends derived from SBUV data

“…We have repeated the analysis of Russell et al . [] with our merged SBUV PMC data set, using our broader latitude bands. At 50°–64°N, we find a decreasing trend in occurrence frequency over 2002–2011 that is not significant.…”

“…Russell et al . [] recently evaluated changes in Northern Hemisphere PMC occurrence frequencies at midlatitudes during 2002–2011, using the 0‐D model of Hervig et al . [] and measured temperature and water vapor data to simulate PMC behavior.…”

“…At 64°–74°N, we find a positive and significant trend, whereas Russell et al . [] shows no trend. This result may be influenced by the fact that SBUV data focuses on bright clouds, while Russell et al .…”

On the Anthropogenic Impact on Long‐Term Evolution of Noctilucent Clouds

“…The observational database on NLC/PMC including microphysical properties, variations with latitude and longitude, solar cycle, and tides has improved significantly in recent decades (see, e.g., Baumgarten et al, 2012;Fiedler et al, 2009;Gerding et al, 2013;Russell et al, 2015). The observational database on NLC/PMC including microphysical properties, variations with latitude and longitude, solar cycle, and tides has improved significantly in recent decades (see, e.g., Baumgarten et al, 2012;Fiedler et al, 2009;Gerding et al, 2013;Russell et al, 2015).…”

Impacts of Cosmic Dust on Planetary Atmospheres and Surfaces

“…One explanation for the increasingly bright clouds is the growing emission of methane since the Industrial Revolution, since this relatively inert gas reaches the stratosphere where it is oxidized to H 2 O. In fact, H 2 O in the stratosphere and mesosphere has been increasing at a rate of ∼1% year −1 since the 1950s (Russell et al 2014). Temperatures in the mesosphere are also decreasing by around −0.5 to −2.0 K decade −1 because of depletion of the stratospheric ozone layer, and increasing greenhouse gases (particularly CO 2 ) which act as refrigerants in the middle atmosphere (Lübken et al 2013).…”