Meridional and vertical out‐of‐phase relationships of temperature anomalies associated with the Northern Annular Mode variability

Abstract

Using the NCAR/NCEP reanalysis, we here present evidence suggesting that the out‐of‐phase relationships of temperature anomalies both between the low and high latitudes and between the stratosphere and troposphere are intimately related to the meridional and downward propagation of anomalies of both signs. The temperature anomalies propagate poleward and downward above the tropopause and propagate equatorward below the tropopause. The characteristic time scale for anomalies of one polarity to propagate from the equator to the pole (or the half period of the complete cycle) is about 55 days. The relatively slow meridional propagation helps to explain the well‐known seesaw oscillatory pattern between low and high latitudes found in monthly data. The equatorward propagation in the troposphere is synchronized with the poleward propagation of the stratospheric temperature anomalies of the opposite sign in both low and high latitudes, responsible for the out‐of‐phase relation between the stratospheric and tropospheric temperature anomalies in the polar region. Since it takes about 55 days for anomalies of one polarity to propagate from the tropics to the pole, such an intimate linkage between the anomalies in the deep tropics and high latitudes would imply a longer lead time for intra‐seasonal climate prediction in the extratropics.