In the 1970s, Madden and Julian discovered that there is a 40–50-day oscillation in tropical circulation and defined it as the ISO, or the Madden-Julian oscillation (MJO) (Madden and Julian, 1971, Madden and Julian, 1972).
Then, the intra-seasonal precipitation moves to southwest China with warm advection and the enhanced westerly wind, which brings the positive relative vorticity advection there. Diabatic heating during precipitation corresponds with warming to the south of the key region, which combines with the temperature advection to weaken the easterly wind and strengths the westerly wind. When there are easterly wind anomalies over the key region, precipitation occurs over the Yangtze River basin and its south.
On the 10–30-day time scale, zonal wind anomalies are associated with precipitation in southern China. The 10–30-day filtered temperature advection to the north of the key region leads to either a decrease or an increase in temperature on the other hand, temperature variations south of the key region have trends opposite of the northern trends, which changes the temperature gradient. The remarkable increase (or decrease) in zonal wind in the key region is mostly determined by temperature anomalies to the north. The propagation of zonal wind oscillation relates to temperature tendencies at different latitudes.
On the 10–30-day time scale, the center of zonal wind anomaly moves eastward. The composite analysis reveals that zonal wind at 200 hPa in this key region has 10–30-day oscillation characteristics.
The results first show that there is an area with large ISO strength in the northwest of the EASWJ in the key region, zonal wind has a dominant period of 10–30 days. Using ECMWF ERA-Interim 6-h reanalysis data, zonal wind intra-seasonal oscillations (ISOs) in the entrance region of the East Asian subtropical westerly jet (EASWJ) in winter from 1979/1980 to 2012/2013 are studied.
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