How Tropical Cyclones Over Tropical Ocean Affect Mid-Latitude Trough

In the Asia-Northwest Pacific region, tropical cyclones (TCs) and mid-latitude troughs act as key atmospheric circulation systems, and their interaction significantly influences regional circulation patterns. This study employs statistical analysis and numerical experiments to reveal the influence of TCs over tropical western Pacific on the East Asia mid-latitude trough (EAMT).

Statistical analysis was conducted by using historical data including the NCEP FNL reanalysis data and JMA TC best track data from June to August between 2001 and 2020. Results indicate that TCs activities can drive the EAMT line to shift northwestward, while simultaneously expanding its north-south extension range and intensifying its strength. The remotely induced geopotential height (HGT) anomalies by TCs serves as a key reason for EAMT location changes, with the EAMT tending to move away from regions exhibiting positive HGT anomalies.

Numerical experiments take TC Maria (2018) as a case study. A control experiment and a TC-removed experiment were carried out with WRF model. Results indicate that TC Maria mainly caused stronger negative HGT anomalies on west side of the EAMT line. When the result obtained by subtracting the HGT anomalies on the east side of the EAMT line from that on the west side was positive (negative), the corresponding EAMT line moved eastward (westward). This indicates that the remote anomalous HGT induced by TC Maria serves as a key factor driving the zonal movement of the EAMT, which confirms the result of the statistical analysis. Reasons for the EAMT zonal movement lies in that TC Maria first induced anomalous cold advection in the mid-latitude regions of the East Asia-Northwest Pacific, which then led to an anomalous decrease in HGT within the EAMT region under the constraint of hydrostatic equilibrium. Since the EAMT line tends to move toward regions with stronger anomalous negative HGT, the TC induced HGT anomalies ultimately resulted in the zonal movement of the EAMT line.

Results of this study provide evidence that remote disturbances induced by TC activities in the tropical oceans can affect weather circulations in the midlatitudes.