Intraseasonal Variability of Air Temperature Over East Asia in Boreal Summer

Abstract

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. It is found that the surface air temperature in EA propagates on a 10-30-day time scale and exhibits a southeastward propagation characteristic. The average zonal and meridional phase speed of the intraseasonal air temperature anomaly is about 2.6 • longitude and 1.7 • latitude per day, respectively. The advection by the mean wind and the advection of the summer mean temperature by the intraseasonal wind primarily contribute to the propagation of the intraseasonal temperature perturbation through the diagnosis of the temperature budget. 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.

Modes of summer temperature intraseasonal oscillations and heatwaves over the Indian region

“…Although much focus is given to modes of ISOs related to rainfall and convectively coupled equatorial waves, especially during the boreal summer monsoon season over the Indian region, it is not studied in great detail if local intraseasonal temperature oscillation exists over the Indian region and if this temperature ISO can be linked to heatwaves or cold waves. Some studies have identified the presence of ISOs of surface temperature over regions such as East Asia (Zhao et al 2017). Over East Asia, the surface temperature was found to propagate south-eastwards at a time-scale of 10-30 d during the boreal summer season.…”

“…Horizontal advection during this season was induced by the advection of intraseasonal temperature anomaly by mean flow and advection of mean temperature by intraseasonal flow. An additional mechanism for the south-eastward propagation was attributed to the upper-tropospheric Rossby wave forcing (Zhao et al 2017). Some studies have also reported modes of interannual variability of temperature over Pakistan (Rashid et al 2022).…”

Diversity in the quasi‐biweekly oscillation sources of the daily maximum temperature over South China during summer

“…Day 0 represents the peak day of the QBWO events [Colour figure can be viewed at wileyonlinelibrary.com] relationship with the mid-to upper-tropospheric height anomaly rather than the lower-tropospheric height anomaly. The correspondence between the mid-to upper-tropospheric height anomaly and the surface temperature anomaly is regulated by the hydrostatic relationship (Zhao et al, 2017).…”

Impacts of MJO on the Intraseasonal Temperature Variation in East Asia

“…Yang and Li (2016) showed that the intraseasonal temperature perturbation in boreal winter propagates southeastward in the mid-high latitudes of Eurasia and gains energy from the mean flow through both kinetic and potential energy conversion. The cause of this southeastward aligned pathway of surface temperatures in East Asia may be related to the topographic effect of the Tibetan Plateau (Yang and Li 2017;Zhao et al 2017). The Tibetan Plateau is the largest and highest plateau in the world with an average elevation exceeding 4500 m (Qiu 2008); therefore, there should be a local intraseasonal variation around the Tibetan Plateau.…”