A Case Study of the Low-Level Jet During an Episode of Spring Convection
Abstract
Circulation and transport of the low-level jet (LLJ) were examined for a case of severe convection that occurred in Spring 1995. Radiosonde observations and Eta model output on constant pressure and isentropic surfaces allowed a detailed examination of the relationship between the LLJ and a subtropical jet (STJ) streak. Height falls associated with a lee cyclone caused an ageostrophic and isallobaric wind that strengthened the LLJ. The smaller horizontal resolution of Eta model grids and hourly forecasts allowed a detailed examination of the LLJ evolution and transport methods. The radiosonde observations, when interpolated to grid points, yielded suspicious results over higher terrain. The hourly forecast of transport variables revealed a step-by-step progression of convection along ridges of equivalent potential temperature advection. The evolution of the LLJ appeared to be influenced by a thermally indirect circulation (TIC) induced in the exit region of a STJ streak. A low-level isallobaric wind responding to a leeside trough and cyclogenesis also effected the LLJ. The TIC is part of the ageostrophic circulation in the exit region of the streak. The low-level isallobaric wind coincided with a trough moving east over the northern Great Plains and a deepening trough in the lee of the Rockies. Results of the case study for the LLJ evolution showed: (1) The LLJ developed beneath a STJ streak exit region as the lower branch of an indirect circulation. (2) A strong cross-contour ageostrophic wind in the lower troposphere aided in accelerating the LLJ. (3) The LLJ strengthened in response to a isallobaric wind associated with lee cyclogenesis.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1997
- Accession Number
- ADA320753
Entities
People
- Christopher S. Donahoe
Organizations
- Air Force Institute of Technology