Lifecycle Of Convective Precipitation Systems over the Arabian Peninsula Using Object Tracking

The Arabian Peninsula (AP) is one of the most arid regions, and precipitation is scarce; it occurs as sporadic and localised convective events (Loung et al., 2020). Numerous studies have focused on studying precipitation in the AP using pixel-wise methods. However, these methods fail to scrutinise the development of precipitation systems from a Lagrangian perspective. A Lagrangian framework can provide valuable insights such as the lifecycle of convective cells and their response to climate change. To address this gap, precipitation in the AP needs to be examined using object-based methods.

We utilise the IMERG V07 data and apply a modified version of the tracking algorithm developed by Seelig et al. (2021, 2023) to obtain precipitation systems (a sequence of object tracks with the possibility of merging and splitting). The tracking algorithm combines overlapping and centroid projection methods, with the centroid projection technique utilising motion vectors derived from particle imaging velocimetry. We use a threshold of 0.5 mm/h to delineate the objects and a threshold of 3 mm/h to filter non-convective systems. Furthermore, we classify the systems into different types using hierarchical agglomerative clustering.

The results show three distinct types of precipitation systems over the AP: a) summer systems (T1), occurring over the southern AP and reaching their peak frequency in August, influenced by the Indian monsoon; b) spring systems (T2), observed over the middle to southern areas of the AP with a peak in April, modulated by extratropical-tropical moisture transport; and c) winter systems (T3), located over the northern AP and peaking in December, impacted by extratropical cyclones entering the AP. The typical life cycle of these systems involves reaching their peak intensity first, followed by maximum precipitation volume, and finally, their largest extent. Nevertheless, T2 systems living longer than 24 hours show varying behaviour. The early afternoon is the most favourable time for rain initiation for T1 and T2 systems, whereas it is the late evening for T3 systems. Most T1 systems cease to rain in the late afternoon. However, both T2 and T3 systems stop around midnight. Generally, systems with merging/splitting objects show higher growth and decay rates than those without merging/splitting.

References:

Luong, T. M., Dasari, H. P., & Hoteit, I. (2020). Extreme precipitation events are becoming less frequent but more intense over Jeddah, Saudi Arabia. Are shifting weather regimes the cause? Atmospheric Science Letters, 21(8), e981. https://doi.org/10.1002/asl.981

Seelig, T., Deneke, H., Quaas, J., & Tesche, M. (2021). Life Cycle of Shallow Marine Cumulus Clouds from Geostationary Satellite Observations. Journal of Geophysical Research: Atmospheres, 126(22). https://doi.org/10.1029/2021JD035577

Seelig, T., Müller, F., & Tesche, M. (2023). Do Optically Denser Trade-Wind Cumuli Live Longer? Geophysical Research Letters, 50(13), 1–8. https://doi.org/10.1029/2023GL103339