Causes of the storm from 24th July to 5th August
At the beginning of late July, there was a blocking anticyclone in Yakutsk at middle and high latitudes and Kamchatka Peninsula, and a steady cold-core cyclone in West Siberia. An upper trough from the cold-core cyclone moved near Chita at 8 o'clock a.m. on the 24th and then changed to be a weak low depression, the trough-line of which was the line started from the middle and westward to Lanzhou via Beijing and a vortex was in Hetao. Subtropical high distributed as a belt and ridge of which was nearly at 20°N. The upper level front spread from Balkhash Lake through Hetao to Northeast China. The vortex in Hetao moved northeast alone the upper level front joined the vortex in Chifeng. There were the two troughs and one ridge type in the high latitude, cold vortex was in West Siberia and eastern of Chita, and there was also a weak ridge, where cold air came. The blocking high and the subtropical high near the Kamchatka Peninsula on the Western Pacific Ocean formed a north-south strip high pressure dam, which blocked the eastward cold air. On 26th July, the low vortex centered into Northeast area and developed strongly, creating a favorable circulation situation for the heavy rain of 26th ~27th.
On the map, the Mongolia cyclone was moved to the Erlian on the 24th, and the low pressure of Hetao generated on the 25th, slowly moved eastward. Cyclone activity in Jianghuai area was active. On the 25th ~27th, the Mongolia cyclone moved and deepened to the Shenyang province southward. Due to the violent development of Mongolia cyclone, the central cyclone which moved to the western part of the Japanese sea merged with the south of the Mongolia cyclone, resulting in a heavy rainstorm in the central part of Jilin province. After midnight on 26th, it started to in Nen River area, and the rainfall mainly occurred on 27th. Heilongjiang province was in the north of high altitude and low vortex. On 29th, the vortex entered Heilongjiang, and later lingered in the west of Heilongjiang Province with a weakened power and on 14 o'clock of 31st, it moved out of Heilongjiang.
Hence, the system taking effect is: the consolidation of trough and vortex in Northeast area, joint eastward Mongolia cyclone and northward Jianghuai cyclone and their violent development.
Causes of the storm from 20th to 22nd August
This rainstorm was caused by northward typhoon 5705. On 10th August, 5705 typhoons generated in the ocean east of Philippines, it moved easterly alone westward flow in the south of the subtropical high and deepen. On the 12th, it turned to the northward direction, on the 13th , it developed into a strong typhoon and continued to go north, and at 8 o'clock of 18th , it moved to 130°E and 23.5°N, and its maximum central pressure was 90600 PA, the maximum wind was 80 meters per second. In 8 o'clock of 20th , it changed to 127°E, 30.5°N, and in 8 o'clock of 21st, it landed at the south of the Korean Peninsula in Busan. After landing, the typhoon continued to move northward, through the east side of Changbai Mountain, Jilin Province, and later weakened to low pressure. The typhoon brought a large number of warm and wet gas flows, coupled with the favorable topography of Changbai Mountain, resulting in the torrential rain in the second Songhua River, the Mudanjiang basin in 21st and 22nd. In the night of 22nd, the typhoon moved north-east out of Heilongjiang.
The information is provided by Disaster Risk Reduction Knowledge Service.
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