East Asian Trough Pattern.

Explanation of the East Asian Trough pattern.

The Asian trough is a semi permanent weather fixture in East Asia that creates weather in the Asian regions. It is created when convergance zones from the Indian Subcontinent and West Pacific Disrupt the 500mb Pressure contours over East Asia.

This disruption then pulls the Northern Isobars and Pressure Gradient at 500mb over North China southwards. This then creates a broad area of weather in East Asia that often affects weather in the area.

The result is the Broad Wide U shaped weather pattern known as a Weather Trough over the East Asia regions. As such there is no low pressure centre but the convergance zones will have stronger 500 mb winds and it is the mixing of Cool Air Jets/Humid Air Jets that forms weather in the South China seas in the example above.

There are graded strengths known as phase associated with the east asian trough formation and this can quickly change mode in winter months from weak to strong and vice versa over the course of a 4 week pattern. There is a strong link between the phase strength of the East Asian trough and a change in temperatures felt in East Asia during winter.

• EAT weak phase winter. Brings warmer climates and air flow to the east asian areas.
• EAT strong phase winter. Will herald Snow-Ice-Sleet and Freezing rain from the Himalayas into the trough inflow. At the south china seas inputs will create rain and or convection (rare) into the EAT.
• The phases of the EAT happen vice versa and normally over a 4 week cycle.
• These phase changes are linked to a EAT shape change of the trough pattern and also the course may alter from a summer, autumn, spring trough.

Depending on other weather factors the trough moves position from time to time and is also affected by seasonal patterns. In the Asian summer may bring rain-convection as in the image above and in the Asian Winter Snow-Ice-sleet and freezing rain from the Himalayas and rain from the south china sea to areas of East Asia.

Summer to Autumn transition last quarter of 2024: At an update for the EAT weather pattern in Sept 9th 2024 as Asia approaches the end of summer and beginning of Autumn we find that Himawari enhanced infrared satellite reveals what is happening with the EAT system.

The East Asian Jet has placed into the North of Asia whilst in the Maritime continent the large continental area has warmed. There is a large area of undisturbed pressure in the Area of Warming in the MC that allows systems to develop upwards in the air column. The EAT has not yet manifested a pattern as the Cool Asian East Jet is placed far north. Also in the Transition area of East China/South Korea/North East China/South Japan there is settled weather but in the Himalayas area a semi-constant area of low pressure interacts with east air masses to create weather there. Low pressure systems in the warming area of South East Asia will develop on the fly so one needs constant monitoring in order to pick up the changes in weather and then to forecast as in such a occasion they will develop rather quickly.