Peter Dalin (IRF)Date:
AulanWhat caused the vast occurrences of noctilucent clouds at middle latitudes in 2020?
Swedish Institute of Space Physics
The seminar is given completely online. See emails for connection details.
The 2020 summer season has revealed vast occurrences of noctilucent clouds (NLCs) in the Northern Hemisphere at middle latitudes (45-55°N). In order to investigate a reason for this NLC extraordinary summer season, we have analyzed long-term Aura/MLS satellite data for all available summer periods from 2005 to 2020. Both Aura/MLS temperature and water vapor in the upper mesosphere and the mesopause region (between 75 and 90 km altitude) have been analyzed.
We have found that there has been a moderate decrease in temperature at the summer mesopause for the past years but no dramatic changes have been observed in temperature in the summer 2020 at the middle latitude mesopause. At the same time, water vapor concentration has dramatically increased (by about 12-15%) in the zonal mean H2O value in the summer 2020, meaning that the summer mesopause at middle latitudes has become more wet. Since NLCs evolution is directly coupled to the amount of water vapor at the mesopause, the water vapor maximum at the summer mesopause was the main reason for vast occurrences of noctilucent clouds seen around the globe in the summer 2020.
Physical mechanisms of the increased amount of water vapor at the mesopause are discussed.
Created 2020-10-02 12:45:53 by Mats HolmströmLast changed 2020-12-09 08:12:46 by Mats Holmström