Special Issue: The 2 nd International Conference on Tropical Meteorology and Atmospheric Science - 2021 IDENTIFICATION OF TROPICAL SQUALL LINE……..………………………………….............. Nurul Izzah Fitria, et al. 31 IDENTIFICATION OF TROPICAL SQUALL LINE USING INFRARED CHANNEL HIMAWARI-8 SATELLITE IMAGERY (CASE STUDY OF 6-7 DECEMBER 2020 IN THE INDIAN OCEAN) Nurul Izzah Fitria 1 *, Novvria Sagita 1,2 , Arnelia Indah Cahyani 1 1 State College of Meteorology Climatology and Geophysics, 5 Perhubungan I Street, Banten, Indonesia, 15221 2 Indonesian Agency for Meteorology Cliotology and Geophysics (BMKG) *E-mail: nurul.laidu@gmail.com Received: 3 September 2021 Revised: 13 May 2022 Accepted: 20 May 2022 ABSTRACT Tropical squall line is a linear type of Mesoscale Convective Systems (MCS) phenomenon. They have regions of both convective and stratiform precipitation. In some cases, the stratiform region of tropical squall also occurs the middle-level vortex, and may contribute to tropical cyclone development. Therefore, the identification of that phenomenon is important. However, the identification of MCS needs observational data which has high time resolution. The next generation of MTSAT satellites (Himawari-8) with better spatiotemporal resolution can be utilized in this study. This study aims to identify the characteristics of cloud line identified as the tropical squall line that occurs in the Indian Ocean south of West Java on December 6-7, 2020 using Himawari-8 Infrared (IR1) satellite imagery. Satellites data are processed using an algorithm adapted to the MCC Maddox criteria. The Maddox criteria describes tropical squall line identified by area coverage of cloud shield more than 100.000 Km 2 and area coverage of interior cold cloud more than 50.000 Km 2 . Furthermore, a subjective interpretation is carried out on the data based on the criteria from previous studies. The result shows that the tropical squall occurred for 19 hours with the initial type of formation as an intersecting convective band and propagating west to southeast around 108.2 o E 9.9 o S. In the mature stage, the precipitation regions develop an asymmetric pattern and shows a vortex (Mesoscale Convective Vortices) that forms inside the stratiform region. The rainfall distribution using the GSMaP model shows a category of heavy rain exceeding 10 mm per hour. Keywords: Himawari-8, tropical squall line, mesoscale convective vortices 1. Introduction Mesoscale Convective Systems (MCS) is a group of Cumulonimbus (CB) clouds that are organized to produce an area of precipitation in one direction at least 100 km long [1]. According to the physical characteristics, organization, and location of occurrence, MCS with 250-2500 km length and time scales > 6 hours divided into two main types: Linear and Circular [2]. Furthermore, Maddox [2] divides the linear type of MCS into two types: squall line that occurs in the midlatitude and tropical squall which occurs in tropical regions. There are four stages of the MCS life cycle: formative, intensive, mature, and decay [3]. The precipitation structure of MCS observed by Leary and Houze [3] generally refers to the linear type; squall line which has a line of convective and stratiform precipitation area [4]. The convective precipitation line developed a group of clouds in the shape of an arc, convex towards the leading edge, the orientation of the lines is generally northeast-southwest, moving rapidly to the east and or south (>10 ms -1 ), and in the form of elongated cells oriented 45 – 90◦ with respect to the line. Meanwhile, the stratiform precipitation region is characterized by an extensive cloud area (> 10 4 km 2 in horizontal area) and concave on the back edge [5]. Furthermore, based on research during heavy rain events over 6 years in Oklahoma [5], two prominent patterns of MCS linear precipitation structures at the mature stage were identified: symmetric (figure 1a) and asymmetric (figure 1b). Figure 1. Precipitation structure of MCS linear in Northern Hemisphere, (a) shows the symmetric pattern and (b) shows the asymmetric pattern [5].