The mixing mechanism of South African cumulus congestus clouds is investigated using a combined observational and modeling approach. The experimental data consists of aircraft measurements collected in developing cloud towers near Nelspruit on three case study days. The observations are analyzed to determine the source regions of the entrained air. The mixing processes are simulated using both axially and slab symmetric cumulus models with very high spatial and temporal resolutions. The simulated clouds have a structured organization with small scale features such as in-cloud downdrafts. The mixing processes are examined by analyzing the time variation of dynamic and thermodynamic quantities along computed parcel trajectories. / Both observations and simulations indicate that most of the entrainment occurs at the cloud top. Evaporative cooling causes downdrafts that transport highly diluted air from the cloud top down to lower levels. The trajectory analysis shows that the penetrative downdrafts are also affected by pressure perturbations. / In the presence of wind shear the downshear sides of the clouds become more diluted, cooler and have stronger downdrafts. The asymmetric organisation is attributed to turbulent exchange of horizontal momentum at the cloud top.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.71976 |
| Date | January 1985 |
| Creators | Reuter, Gerhard Wilhelm. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Meteorology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000219537, proquestno: AAINL20837, Theses scanned by UMI/ProQuest. |
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