Schalkwyk et al. (2025) Observations of a dryline interacting with a back-building mesoscale convective system in the Kalahari region of southern Africa

Identification

• Journal: Atmospheric Research
• Year: 2025
• Date: 2025-12-11
• Authors: Lynette van Schalkwyk, Ross C. Blamey, Callum Munday, Richard Washington, C. J. C. Reason
• DOI: 10.1016/j.atmosres.2025.108694

Research Groups

• Department of Oceanography, University of Cape Town, South Africa
• University of Oxford, UK

Short Summary

This study analyzes a unique set of observations to describe the environment and development of a back-building mesoscale convective system (MCS) interacting with a dryline in the southern Kalahari region. It reveals that the MCS developed in a highly unstable, weakly sheared environment, with back-building and strong low-level inflow extending its lifespan and contributing significantly to regional rainfall.

Objective

• To analyze the observed environment and development characteristics of a back-building mesoscale convective system (MCS) that formed along a dryline in the semi-arid southern Kalahari region of southern Africa.

Study Configuration

• Spatial Scale: Southern Kalahari region of southern Africa, encompassing parts of northwestern South Africa, southwestern Botswana, and southeastern Namibia.
• Temporal Scale: 28 and 29 December 2023, with the MCS exhibiting a lifespan of at least 13 hours.

Methodology and Data

• Models used: Not applicable (observational study). MCS classification was based on Cold Cloud Shield (CCS) criteria (contiguous CCS area exceeding 40,000 km², outer cloud shield brightness temperature < 241 K, inner core brightness temperature < 225 K).
• Data sources: Unique set of in-situ observations, station data, and soundings. Satellite data (brightness temperature) was implicitly used for MCS classification.

Main Results

• The MCS developed along a dryline in a highly unstable (CAPE > 1000 J kg⁻¹, MU-CAPE > 3000 J kg⁻¹), but weakly sheared environment.
• Near-surface moisture gradients along the dryline exceeded 6 g kg⁻¹ (100 km)⁻¹ during morning and evening of 28 December.
• Convection initiated adjacent to the dryline, with individual storm cells merging to form the MCS. New cells continued to develop along the dryline and were steered downstream by mid-level northwesterly winds.
• Back-building and a strong northeasterly low-level inflow contributed to renewed development along the storm’s axis during the night-time, extending its lifespan to at least 13 hours.
• The MCS resulted in widespread rainfall, roughly equivalent to the December–February average for the region, causing localized flooding and power failures.

Contributions

• Provides new insights into the contribution of MCSs to seasonal rainfall in the southern Kalahari region.
• Offers a valuable observational example of mesoscale interactions between a dryline and individual storm cells, particularly during night-time.
• Utilizes a unique set of observations to detail the environmental conditions conducive to such a back-building MCS.

Funding

• Not specified in the provided text.

Citation

@article{Schalkwyk2025Observations,
  author = {Schalkwyk, Lynette van and Blamey, Ross C. and Munday, Callum and Washington, Richard and Reason, C. J. C.},
  title = {Observations of a dryline interacting with a back-building mesoscale convective system in the Kalahari region of southern Africa},
  journal = {Atmospheric Research},
  year = {2025},
  doi = {10.1016/j.atmosres.2025.108694},
  url = {https://doi.org/10.1016/j.atmosres.2025.108694}
}