Local Front and Convergence Lines

　日本語　

Mountainous and other terrain features can bring not only strong winds, but also wind convergence lines and local fronts that are not analyzed on a weather chart scale.

Local Front

Local fronts can generate cumulonimbus clouds or increase precipitation due to sudden changes in wind and temperature. Kusaka Laboratory studies local fronts in the Kanto region, which are generated by low pressure systems over the Sea of Japan and along the southern coast of Japan. Local fronts in the Kanto region are several hundred kilometers long and several hundred meters thick. They are also said to be generated when warm air from the ocean slides up into the cold air layer generated inland of the Kanto region. Kusaka and Kitahata (2009) investigated the relationship between precipitation patterns observed when cold fronts pass through the Japanese archipelago and local fronts.

The following patterns of radar precipitation during the passage of a cold front are called:

(a) widespread type, (b) Hokuriku type, and (c) jump type.

from Kusaka and Kitahata (2009)

Convergence Lines

We have been studying convergence lines that occur at the leeward side of mountains, focusing on banded cumulus sequences that outbreak on the Pacific side of Japan. The most famous convergence line is called "Japan Sea Cold Air Cluster Convergence Zone (JPCZ)", but there is also the "Boso front", which occurs downwind of the Chubu mountains, and convergence lines that outbreak leeward of the Kii and Shikoku mountains. Even the convergence lines that outbreak on the Pacific side are of interest because they produce rainfall, snowfall, tornadoes, and other wind gusts. We are currently studying the different locations of convergence lines and the mechanism of their movement, as well as the formation mechanism of banded cumulus sequences.

True-color reproduced image of Himawari-8 on December 26, 2021 at 14:00 JST.

From National Institute of Information and Communications Technology (NICT)

(Written by: Nobuyasu Suzuki; Edited by: Angela Magnaye)

Room 301 in the Center for Computational Sciences, 1-1-1, Tennodai Tsukuba, Ibaraki 305-8577, Japan