A Case Study of Mass Transport during the East-West Oscillation of the Asian Summer Monsoon Anticyclone

Abstract

We use ERA-Interim reanalysis, MLS observations, and a trajectory model to examine the chemical transport and tracers distribution in the Upper Troposphere and Lower Stratosphere (UTLS) associated with an east-west oscillation case of the anticyclone in 2016. The results show that the spatial distribution of water vapor (H 2 O) was more consistent with the location of the anticyclone than carbon monoxide (CO) at 100 hPa, and an independent relative high concentration center was only found in H 2 O field. At 215 hPa, although the anticyclone center also migrated from the Tibetan Mode (TM) to the Iranian Mode (IM), the relative high concentration centers of both tracers were always colocated with regions where upward motion was strong in the UTLS. When the anticyclone migrated from the TM, air within the anticyclone over Tibetan Plateau may transport both westward and eastward but was always within the UTLS. The relative high concentration of tropospheric tracers within the anticyclone in the IM was from the east and transported by the westward propagation of the anticyclone rather than being lifted from surface directly. Air within the relative high geopotential height centers over Western Pacific was partly from the main anticyclone and partly from lower levels.

Comparison of Electrochemical Concentration Cell Ozonesonde and Microwave Limb Sounder Satellite Remote Sensing Ozone Profiles for the Center of the South Asian High

“…Nevertheless, in the lower stratosphere (especially at 83, 68, and 56 hPa), the relative difference between MLS ozone and ozonesonde over Shiquan River in the central region of the South Asian high is less than that [13] over Lhasa, Tengchong, and Naqu, which are located in the east of the South Asian high center. That may be attributed to the steady situations in the central region and the mutable conditions in the east location during the east-west oscillation (eastward-westward migration) of the Asian Summer Monsoon Anticyclone (the South Asian high) [26]. According to the linear regression relationship between MLS and ozonesonde data, in most of the lower and middle stratosphere, the slopes are slightly less compared with the three stations in the east of the South Asian high [14], while the relative intercepts of α/O 3sonde are generally greater, which also indicates a larger system deviation of MLS at Shiquan River in the center of the South Asian high.…”

Zonal scale and temporal variability of the Asian monsoon anticyclone in an idealised numerical model

“…The simple steady theory developed by Matsuno (1966) and Gill (1980) for heat-induced tropical flows is widely used to explain the general structure of the monsoon circulation. The Gill-Matsuno model describes the response to a localised, low-latitude heating in terms of westwardpropagating Rossby waves and eastward-propagating equatorial Kelvin waves, where the importance of the latter strongly depends on the position of the heating relative to the Equator.…”

Comment on wcd-2020-64

“…These oscillation events can include a split of the monsoon anticyclone and a zonal shift of its geopotential height maximum. Luo et al (2017) further show that this shift can lead to a substantial zonal mass flux and thus might have important implications for horizontal transport. They further link the oscillatory behaviour to a bi-modality of the monsoon, as it was described by Zhang et al (2002).…”

“…They find a strong correlation between the eastward extension and anomalous heat and rainfall patterns over east Asia, indicating a potential meteorological impact of eastward shedding events. Similarly, Luo et al (2017) describe and analyse an east-west oscillation event of the monsoon anticyclone during 2016. These oscillation events can include a split of the monsoon anticyclone and a zonal shift of its geopotential height maximum.…”