Search Results

You are looking at 1 - 2 of 2 items for

  • Author or Editor: Ernst Klinker x
  • Refine by Access: All Content x
Clear All Modify Search
Ernst Klinker
and
Prashant D. Sardeshmukh

Abstract

The momentum budget for January 1987 is evaluated with global observations analyzed at the European Centre for Medium-Range Weather Forecasts (ECMWF). The dissipation term is diagnosed from the budget as a balance requirement, that is, as that required to balance the sum of the advection, Coriolis, pressure gradient, and local tendency terms. This is then compared with the parameterized subgrid-scale effects in the ECMWF model's momentum equation, with a view of identifying possible errors in those parameterizations.

The balance requirement does not support the high parameterized values of orographically induced gravity-wave drag in the lower stratosphere. A deeper analysis also does not suggest a major role for turbulent vertical transports above the boundary layer. On the other hand, our budget does indicate that more effort be spent on a better representation of the potential enstrophy cascade associated with Rossby wave breaking in the upper troposphere. These statements are qualified by the errors in the balance requirement itself. The extent to which this is a problem is discussed.

A distinctive feature of these calculations is their internal consistency., that is, all the terms in the budget are evaluated as in the version of the ECMWF model used for assimilating the observations. This offers several advantages, not the least of which is that it makes our budget residuals identical to the systematic initial tendency errors of the operational weather forecasts, thus facilitating their computation and routine monitoring. As such, our calculations explain a large fraction of the systematic short-range forecast errors and, because of their local character, provide clues as to the possible sources of those errors. Experiments with and without gravity-wave drag are described to illustrate its large contribution during this period to the southerly wind error of the operational weather forecasts at 70 mb over western North America.

Full access
Alan K. Betts
,
Christopher S. Bretherton
, and
Ernst Klinker

Abstract

The relationship between boundary-layer thermodynamic structure and cloud fields and their diurnal variation are explored using seven days of data from dw R/V Valdivia during the Atlantic Stratocumulus Transition Experiment. Cloudiness is at a maximum before dawn, when the boundary layer (BL) has the thermodynamic structure of a partially mixed, conditionally unstable stratocumulus layer, which is close to mean saturation below the inversion. Cloudiness falls during the daytime, and in the late afternoon the BL has two distinct layers: a warmer, drier cloud layer (characteristic of trade cumulus) above a more well-mixed subcloud layer. The observed mean profiles are consistent with an earlier suggestion that there is a cloud-cover transition once the BL mixing-line slope exceeds half that of the moist adiabat. In contrast, the BL structure in the ECMWF model for the same week has a much drier, warmer, more stable “cloud” layer than the observations.

Full access