Abstract

The intraseasonal oscillation (ISO) of atmospheric temperature at 2m over East Asia (EA) in boreal summer is investigated through NCEP-NCAR reanalysis data for the period of 1979-2013. It is found that the surface air temperature in EA has a dominant period of 10-30 days and exhibits a southeastward propagation characteristic. The average zonal and meridional phase speed of the intraseasonal air temperature anomaly is about 2.6 longitudes and 1.7 latitudes per day, respectively. A diagnosis of the temperature budget suggests that the propagation of the intraseasonal temperature perturbation is primarily attributed to the advection by the mean wind and the advection of the summer mean temperature by the intraseasonal wind. An upper-tropospheric geopotential positive (negative) height anomaly is closely associated with a low-level warmer (cooler) air temperature anomaly and both anomalies propagate southeastward in a similar way. A wave activity flux analysis reveals that mid-latitude Rossby wave energy also propagates southeastward, consistent with the upper-tropospheric geopotential height propagation. This indicates that in addition to low-level advection mechanism, upper-tropospheric forcing through the hydrostatic relationship is another possible mechanism. A further statistical analysis indicates that heat waves in EA summer are modulated by the southeastward-propagating intraseasonal temperature mode.

Highlights

  • The Intraseasonal Oscillation (ISO) is one of the dominant modes in tropical atmosphere

  • On the other hand, tropical ISO is characterized by northward propagations in the Intraseasonal Variability of Air Temperature

  • Whereas none of the heat wave events appear in the inactive phase of ISO. This indicates that the intraseasonal temperature variation studied here greatly modulates the occurrence of heat wave events in eastern China

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Summary

Intraseasonal Variability of Air Temperature Over East Asia in Boreal Summer

Chen Zhao 1, Tim Li 1, 2*, Suxiang Yao 1, Swadhin K. The intraseasonal oscillation (ISO) of atmospheric temperature at 2 m over East Asia (EA) in boreal summer is investigated through NCEP-NCAR reanalysis data for the period of 1979–2013. An upper-tropospheric geopotential positive (negative) height anomaly is closely associated with a low-level warmer (cooler) air temperature anomaly and both anomalies propagate southeastward in a similar way. A wave activity flux analysis reveals that mid-latitude Rossby wave energy propagates southeastward, consistent with the upper-tropospheric geopotential height propagation. This indicates that in addition to low-level advection mechanism, upper-tropospheric forcing through the hydrostatic relationship is another possible mechanism. A further statistical analysis indicates that heat waves in EA summer are modulated by the southeastward-propagating intraseasonal temperature mode

INTRODUCTION
Intraseasonal Variability of Air Temperature
DATA AND METHOD
FEATURES OF STRUCTURE AND EVOLUTION OF INTRASEASONAL TEMPERATURE ANOMALY
SOUTHEASTWARD PROPAGATION MECHANISMS
Findings
CONCLUSIONS AND DISCUSSIONS
Full Text
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