Moisture Sources for Tropical Cyclones Genesis in the Coast of West Africa through a Lagrangian Approach

Abstract

Atmospheric moisture transport plays an important role in the genesis of tropical cyclones (TCs). In this study, the moisture sources associated with the genesis of TCs in the tropical Atlantic Ocean near West Africa, from June to November in the period 1980-2018 were identified. To detect the location of the TCs genesis was used the HURDAT2 database from the National Hurricane Center. Besides global outputs of the Lagrangian FLEXPART model were used to determine the moisture sources that provided water vapor for the genesis of TCs. This model permitted to track backward in time the air masses from the genesis region of the TCs and identify those regions where air masses uptake moisture before reach the target regions. The results reveal that 18.1% (108 TC) of the total number of TCs formed in the North Atlantic basin were originated in the region of study. The major frequency for the TCs genesis was observed in August and September, each one representing approximately 45% of the total. The transport of moisture associated with the genesis of TCs mainly comes from the east of the North and South Atlantic Ocean, as well as from West Africa and the Sahel region. The patterns of moisture uptake confirmed an interhemispheric moisture transport. Finally, during the El Niño, the moisture uptake is more intense over the Atlantic Ocean close to West Africa around 15 °N of latitude, while during La Niña the pattern is slightly weaker, but it covers a wider area over the Atlantic Ocean and the north of Africa.

Moisture Sources for Precipitation Associated With Major Hurricanes During 2017 in the North Atlantic Basin

“…Pazos and Gimeno (2017) and Pérez‐Alarcón et al. (2021a), also using the FLEXPART model, accounted for the water budget associated with all the TCs whose origin is over the eastern part of the North Atlantic Ocean basin (near the West African coast); both studies differ in the period analyzed (1979–2012 and 1980–2018, respectively), and in the definition of the target regions. Pazos and Gimeno (2017) defined the target region as a fixed box between 8°–20°N and 15°–45°W, and the whole area was analyzed when a TC occurred.…”

“…Thus, in this study, by applying the Lagrangian moisture source diagnostic method proposed by Sodemann et al (2008), we investigated the moisture transport and sources that produced precipitation during the entire trajectories along their complete lifecycle of the six TCs that reached the MH category in the North Atlantic basin in 2017. In addition to improving the previous studies (e.g., Pazos & Gimeno, 2017;Pérez-Alarcón et al, 2021a), we assumed variable target regions defined by the outer radius of TCs in each position of each TC trajectory.…”

“…Similarly, Yang et al (2017) analyzed the moisture sources for Typhoon Nina (in 1975) by using the Lagrangian analysis tool LAGRANTO developed by Sprenger and Wernli (2015) fed by downscaled Weather Research and Forecasting (WRF) model simulations. Pazos and Gimeno (2017) and Pérez-Alarcón et al (2021a), also using the FLEXPART model, accounted for the water budget associated with all the TCs whose origin is over the eastern part of the North Atlantic Ocean basin (near the West African coast); both studies differ in the period analyzed (1979-2012 and 1980-2018, respectively), and in the definition of the target regions. Pazos and Gimeno (2017) defined the target region as a fixed box between 8°-20°N and 15°-45°W, and the whole area was analyzed when a TC occurred.…”

Where does the moisture for North Atlantic tropical cyclones come from?

“…These terrestrial sources involve complex hydroclimatic interactions in several atmospheric processes at different time scales, such as low-level atmospheric moisture transport and the West African monsoon (Lélé et al 2015;Redelsperger et al 2002Redelsperger et al , 2006. Most recently, Pérez-Alarcón et al (2021a) improved the findings of Pazos and Gimeno (2017) by considering a variable target region, defined as the area within the TCs outer radius (Pérez-Alarcón et al 2021b). Although Pazos and Gimeno (2017) and Pérez-Alarcón et al (2021a) provided new insights into the contribution of atmospheric moisture to the genesis of TCs in the North Atlantic, they did not provide a complete overview of all TC phases over the entire basin.…”

“…Most recently, Pérez-Alarcón et al (2021a) improved the findings of Pazos and Gimeno (2017) by considering a variable target region, defined as the area within the TCs outer radius (Pérez-Alarcón et al 2021b). Although Pazos and Gimeno (2017) and Pérez-Alarcón et al (2021a) provided new insights into the contribution of atmospheric moisture to the genesis of TCs in the North Atlantic, they did not provide a complete overview of all TC phases over the entire basin. Therefore, no study has identified the source regions of moisture for the different evolution phases of TCs in the North Atlantic Ocean basin.…”