Abstract
Long-term systematic observations of noctilucent clouds in the regions of Moscow (Russia), Vilnius (Lithuania), and La Ronge (Canada) are considered. Variables, describing the seasonal activity of noctilucent clouds, are discussed. It is shown that there are no statistically significant trends within time intervals of several recent decades. This result is compared to other known findings on trends in mesospheric clouds. Based on the data of the modern ground-based noctilucent cloud observing network in the northern hemisphere and simultaneous satellite data on mesospheric temperature and humidity, we estimate sensitivity of noctilucent clouds to the relative humidity of the upper mesosphere. Such an approach allows us to discuss possible changes of the upper-mesospheric relative humidity, which are consistent with a zero secular trend in noctilucent cloud activity.
Highlights
Long-term systematic observations of noctilucent clouds in the regions of Moscow (Russia), Vilnius (Lithuania), and La
The different approaches arrived to controversial conclusions on the subject which suggest either continuously increasing noctilucent clouds (NLC) numbers over Western Europe (Gadsden 1990, 1998) and polar mesosphere clouds (PMC) activity for sub-polar and polar latitudes
The established relationship between the time series describing the NLC/PMC activity, temperature, and water vapor (Hervig and Siskind 2006; Lübken et al 2009) poses an important question what conclusions about the physical state of summer mesosphere may be obtained from the zero NLC trend result
Summary
Long-term systematic observations of noctilucent clouds in the regions of Moscow (Russia), Vilnius (Lithuania), and La. 2009) and zero trend in NLC occurrence frequency, is reduced to a great extent when considering the same time intervals and the same latitude range (50 to 64°N) for PMC (Shettle et al 2009) and for NLC data sets.
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