Monday, 23 January 2017
Seasonal variability of Arctic and extratropical tropopause is analyzed to understand detailed physical characteristic of the middle atmosphere. The seasonal cycle of tropopause pressure for the 150 winter days is extracted from 36-year (1979-2015) NCEP daily reanalysis data applying cyclostationay EOF analysis (CSEOF). Corresponding evolution of key variables is obtained from the ERA interim daily reanalysis data for the same period. The seasonal cycle describes the seasonal evolution of the tropopause pressure; the tropopause pressure is highest in January/February in mid-latitudes while the maximum tropopause pressure appears in March in high-latitudes. Principal component shows that its intensity has fluctuated by ~50% during the data period. The variability of tropopause pressure is highly correlated with that of potential vorticity and other variables near the tropopause. Low-frequency undulation of tropopause pressure in high latitude is significantly connected with stratospheric air temperature and geopotential height anomaly, which exhibits downward propagation from the upper stratosphere. On the other hand, mid-latitude tropopause variability is much strongly with the anomalous geopotential height in the troposphere and anomalous air temperature above and below the tropopause. High-frequency component of tropopause pressure variability captures eastward propagating signals, particularly in the region between the Arctic and the extratropical region.
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