6TROPICAL TRACKING MESOSCALE CONVECTIVE SYSTEM CORES, OVER NORTHERN SOUTH AMERICA, USING OVERLAPPING TECHNIQUE

It has been observed in recent years that usually, during the hurricane season, at least 1 hurricane or tropical storm takes place approaching the northern tip of South America or even traveling across it. That was the case of hurricane Julia in October 2022 and the tropical storm Franklin that occurred on August 2023. Even if the core of the storm does not cross northern South America, the mesoscale convective systems and particularly its core, which form in the surrounding storm bands, can cause severe economic damages and life threats. Thus, the real time tracking of these systems can provide valuable information for forecasting and researching purposes.

In order to track the convective cores (CC) of the mesoscale convective system, the areas of the goes ir image (10 μm) with brightness temperature less or equal to 215 k (i.e., the core of the cloud mesoscale system) are initially identified and then tracked in subsequent images every 10 minutes. Once a CC is detected, its geometric center is determined and followed by means of the overlapping procedure. This overlapping technique was first described by (Wielicki & Welch, 1986, Williams & Houze, 1987) and recently used by (Feng e.a. 2021) This technique consists in the following: If, within two successive IR images, a CC overlaps itself by more than 25% of its area, this cloud system is considered as the same system and its track continues. A line connecting the different positions (with time) of the geometrical center of the CC is then drafted. When two or more CC merge together, the largest overlapped CC is assumed to continue and the smaller overlapped CC are terminated. Similarly, when a CC splits into several smaller CC, only the largest overlapped fragment continues carrying the characteristics of the original system.

The proof of concept of this technique was tested with the tropical storm Franklin while approaching the Caribbean coast of Guyana, Venezuela and Colombia, on 19 - 20 August 2023.

In august 20, At 02:40z the tropical storm Franklin (F, hereafter) was located (approximately) at 63W 13N. At this time, several hundred km south of F, at 66W 6N a convective core (CC1) was registered. This CC1 which formed, about 2 hours earlier within one of the bands of F, and it had (at this time) an area of about 15000 km² and continued developing to the west. Approximately 1 hour later, several hundred km to the west of this CC1, another convective core (CC2) formed at 71W 6N near to Arauca Colombia. The formation of this second CC2, developed during the nocturnal convection, apparently had no relationship with the F storm bands. This second CC2 continued its development to the north and east directions. 6 hours later, at 10:20Z these two systems merged and formed a wide convective system. The new system occupied an area larger than 36000 km² and began dissipating approximately at 14:00z.

Besides the occupied area, the implemented technique provides information about: direction, time and place of initiation and dissipation of the CC. Also, the difference between the minimum brightness temperature of the CC and the temperature of the tropopause at this point, was computed and used as an index of the intensity of the storm.

This technique can be useful for nowcasting severe storm weather warning and for research studies involving diurnal - nocturnal convection, mountain – valley and sea breeze circulations.