This study shows the variability of polar cold air mass amount below potential temperature of 280 K, and north of 45N can be understood with a concept of charge and discharge, where anomalously large daily discharge indicates an intermittent occurrence of cold air outbreak. The polar cold air mass amount north of 45N gradually charges up due to diabatic cooling but dramatically discharges due to cold air outbreak with a pulse width of about 5 days. Cold air outbreaks tend to bring colder winter in East Asia and the east coast of North America, while warmer winter prevails on the northern side of these regions. The cold air mass amount south of 45N increases just after a cold air outbreak but returns to the normal level soon because of its life time of about 3 days. Therefore, monthly mean of total cold air mass amount in the Northern Hemisphere is negatively correlated with the monthly mean discharge.
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