Dominant patterns of winter-time intraseasonal surface air temperature over the CONUS in response to MJO convections

Abstract

The dominant patterns of the intraseasonal surface air temperature (SAT) over the Contiguous United States (CONUS) during wintertime (December–March) are investigated in the period of 1979–2014 in the present study. The first two leading modes revealed by the empirical orthogonal function (EOF) analysis sufficiently represent the patterns by explaining nearly 80% of the total variance. The EOF1 mode has a monopole pattern with large loadings in the central-north CONUS, while the EOF2 has a dipole pattern with loadings of opposing signs in the northwestern and southeastern CONUS. The monopole pattern of the EOF1 has a significant lead-lag correlation with the EOF2 dipole pattern. These dominant patterns are traced back to the convective anomalies of the Madden–Julian Oscillation (MJO) which has eight phases characterized by the revised real-time multivariate MJO index. The connections are established dynamically by Rossby wave trains propagating from the MJO convections to North America. Specifically, the monopole warming (EOF1) is well developed by lagging about two pentads from enhanced MJO convections during phase 4 over the Maritime Continent as the wave sources. The dipole pattern (EOF2) of “warm-West/cool-East” starts to develop during MJO phase 7 with enhanced convections over the Western Pacific and reaches a maximum about two pentads later. Such dynamic lead-lag relationships on intraseasonal time scales are revealed by both diagnostic analysis and numerical experiments using a linear baroclinic model, which are potentially useful for predicting intraseasonal variations in SAT over the CONUS.