Search Results

You are looking at 1 - 2 of 2 items for :

  • Author or Editor: J. Bradford x
  • Journal of the Atmospheric Sciences x
  • Refine by Access: All Content x
Clear All Modify Search
J. Bradford
,
A. S. Berman
, and
T. S. Lundgren

Abstract

The interfacial stability of two differentially rotating fluid layers in a tall, right circular cylinder is investigated analytically and experimentally. The differential speeds are such that the Ekman and Rossby numbers of the flow are small. A linearized stability analysis, including interfacial tension and viscous effects at the interface and end caps is performed on the nongeostrophic equations of motion. The nongeostrophic nature of the perturbed flow is due to the large height to radius ratio of the cylinder. The results yield stability boundaries which can be compared to quasi-geostrophic predictions for the same system. The nongeostrophic effects are found to stabilize the flow relative to the quasi-geostrophic predictions with the exception of narrow regions or “spikes” of instability in parameter space which are not accounted for by the quasi-geostrophic equations.

Experiments are conducted in which stability boundaries corresponding to wavenumbers n = 1 and n = 2 are determined. Good agreement is found with the viscous, nongeostrophic predictions, including a clear experimental reproduction of the distinctive “spike regions”. Qualitative observations also are made of amplitude and frequency modulated finite-amplitude baroclinic waves in the unstable regions.

Full access
Chuixiang Yi
,
Kenneth J. Davis
,
Bradford W. Berger
, and
Peter S. Bakwin

Abstract

Time series of mixed layer depth, zi, and stable boundary layer height from March through October of 1998 are derived from a 915-MHz boundary layer profiling radar and CO2 mixing ratio measured from a 447-m tower in northern Wisconsin. Mixed layer depths from the profiler are in good agreement with radiosonde measurements. Maximum zi occurs in May, coincident with the maximum daytime surface sensible heat flux. Incoming radiation is higher in June and July, but a greater proportion is converted to latent heat by photosynthesizing vegetation. An empirical relationship between zi and the square root of the cumulative surface virtual potential temperature flux is obtained (r 2 = 0.98) allowing estimates of zi from measurements of virtual potential temperature flux under certain conditions. In fair-weather conditions the residual mixed layer top was observed by the profiler on several nights each month. The synoptic mean vertical velocity (subsidence rate) is estimated from the temporal evolution of the residual mixed layer height during the night. The influence of subsidence on the evolution of the mixed, stable, and residual layers is discussed. The CO2 jump across the inversion at night is also estimated from the tower measurements.

Full access