Polar Atmosphere Phenomena
: Focusing on the Polar Vortex
SSW
1. Number of occurrences of SSW based on ERA5 Reanalyzing
The data is a table that summarizes the number of SSW occurrences from the 1960s to the 2010s. Although we tried to predict the number of SSW occurrences in the future by analyzing the trend of occurrence,
it is difficult to draw a definite conclusion on the trend of occurrence
due to the large volatility of the number of SSW occurrences by period.
* Several datasets such as NCEP-NCAR, ERA40, ERA-Interim, JRA-55, MERRA2, and ERA5 existed in the referenced data table, but ERA5 provides the mostup-to-date high-resolution data and deals with the highest number of occurrences.
Therefore, data1 was based on ERA5. (reconstructed to 1 hour interval, 0.25°)
2. Analysis of u850, precipitation, and temperature
when SSW occurs in winter using SEAS5 re-analysis data
This data is a map showing the degree of change in response in the troposphere in the northern hemisphere (20-80 degrees latitude)
when SSW occurs in winter (December-March). Reactions in the troposphere are noticeable mainly in December and January.
From March, the stratospheric polar vortex completely weakens and the stratospheric-troposphere bond weakens for seasonal reasons.
Therefore, no significant deviation from the average is observed.
① u850
In the case of u850, the sudden of the medium-high latitude decreases to 2.0 m/s, and the low-medium latitude increases to 1.5 m/s. When SSW occurs, the vortex weakens, which affects the troposphere, weakening the jet flow in the troposphere and, as a result, decreasing the u850 wind speed in the high latitude region. At the same time, in the mid-latitude region, the wind tends to strengthen relatively due to jet shift. (As the high-altitude wind weakens, the wind is driven toward the low-altitude direction - related to energy conservation.
② Precipitation
In the case of precipitation, in the medium-high latitudes decrease by 1.00mm/day in some areas, and in the medium-high latitudes increase by 1.00mm/day. In the high latitudes, as the jet stream weakens, polar typhoon activity decreases and precipitation decreases. On the other hand, in the case of low medium latitudes, as the cold air goes south, the probability of typhoon development increases and precipitation increases.
③ Temperature
In the case of temperature, the medium-high latitudes’ temperature decreases by 1.00°C, and the low medium latitudes’ temperature increases by 1.00°C depending on the region. This is a phenomenon that occurs as the polar cold air moves as the polar vortex weakens. At low latitude, the temperature in some regions shows a slight increase due to thermal relocation, but in general, there is no significant change as the polar region has little effect. In fact, even on the map above, temperature changes appear only in very limited areas.
Therefore, sudden stratospheric warming (SSW) causes all wind strength, precipitation, and temperature to change on average. It causes dry and cold weather, especially in northern Europe.