Engineering topics

Koehler, T. L.

Publications and source records attributed to Koehler, T. L..

6 records

NASA NTRS1986

A terrain-dependent reference atmosphere determination method for available potential energy calculations

An iterative technique that determines the reference atmosphere which incorporates the effects of uneven surface topography is presented. This method has been successfully applied in several available potential energy studies. An alternative method due to Taylor is also evaluated. While Taylor presented excellent continuous formulations of the available potential energy that include topography, his method for determining the reference atmosphere distributions failed to provide the accuracy needed to produce reliable available potential energy estimates. Since topography has a significant influence on the general circulation, it is important to employ techniques that incorporate its effects in the determination of available potential energy.

Koehler, T. L.↗

NASA NTRS1983

An evaluation of soundings, analyses and model forecasts derived from TIROS-N and NOAA-6 satellite data

TIROS-N and NOAA-6 temperature soundings over North America during three days in January 1980, and synoptic analyses and numerical-model forecasts derived from them, are compared with conventional data and analyses from NMC's limited-area fine-mesh model (LFM). The collocated sounding comparison revealed significant errors, especially near the surface and the tropopause. Satellite-derived thermal gradients were found to be weak, and thickness-analysis difference fields to propagate eastward, suggesting that sounding errors are correlated with synoptic patterns. The same pattern of anomalies is seen in the model forecasts. More detailed determinations of the correlation detected here could be used to optimize the assimilation of satellite soundings to conventional data.

Koehler, T. L.↗

NASA NTRS1981

Optimum employment of satellite indirect soundings as numerical model input

The characteristics of satellite-derived temperature soundings that would significantly affect their use as input for numerical weather prediction models were examined. Independent evaluations of satellite soundings were emphasized to better define error characteristics. Results of a Nimbus-6 sounding study reveal an underestimation of the strength of synoptic scale troughs and ridges, and associated gradients in isobaric height and temperature fields. The most significant errors occurred near the Earth's surface and the tropopause. Soundings from the TIROS-N and NOAA-6 satellites were also evaluated. Results again showed an underestimation of upper level trough amplitudes leading to weaker thermal gradient depictions in satellite-only fields. These errors show a definite correlation to the synoptic flow patterns. In a satellite-only analysis used to initialize a numerical model forecast, it was found that these synoptically correlated errors were retained in the forecast sequence.

Horn, L. H.↗

NASA NTRS1981

A case study of height and temperature analyses derived from Nimbus-6 satellite soundings

Height and temperature analyses were constructed on a subset of the LFM grid using only Nimbus-6 satellite temperature profiles from approximately 1800 GMT 22 Feb. 1976. Several experiments were performed to evaluate various features of these satellite derived analyses. Fields derived from the bracketing LFM analyses provide the verification data. The results indicate that Nimbus-6 soundings were able to correctly position the major troughs and ridges, but underestimate gradients in the analyses due primarily to the soundings being too warm in the troughs. No advantage could be found in using a set of satellite soundings with a greater horizontal resolution than the DST soundings.

Koehler, T. L.↗

NASA NTRS1981

Evaluation of TIROS-N and NOAA-6 satellite data: Comparisons of colocated soundings and analyses for a January case

An early January 1980 synoptic situation was used in evaluating the performance of TIROS-N and NOAA-6 operational temperature soundings. Visual and statistical comparisons of temperature and thickness fields were employed to determine the effects of manual screening of the satellite soundings and measure the accuracy of both the satellite soundings and analyses derived from them. Comparisons between the performance of TIROS-N and NOAA-6 were emphasized. Both satellites were able to correctly position the major troughs and ridges. Gradients were underestimated though, with troughs markedly too warm and ridges slightly too cold. The poorest data occurred near the surface and tropopause as reflected by larger standard deviations in those layers. The performance of TIROS-N was slightly superior to that of NOAA-6.

Schmidt, B. D.↗

NASA NTRS1981

A numerical evaluation of TIROS-N and NOAA-6 analyses in a high resolution limited area model

Vertical temperature profiles derived from TIROS-N and NOAA-6 radiance measurements were used to create separate analyses for the period 0000 GMT 6 January to 0000 GMT 7 January 1980. The 0000 GMT 6 January satellite analyses and a conventional analysis were used to initialize and run the University of Wisconsin's version of the Australian Region Primitive Equations model. Forecasts based on conventional analyses were used to evaluate the forecasts based only on satellite upper air data. The forecasts based only on TIROS-N or NOAA-6 data did reasonably well in locating the main trough and ridge positions. The satellite initial analyses and forecasts revealed errors correlated to the synoptic situation. The trough in both TIROS-N and NOAA-6 forecasts which was initially too warm remained too warm as it propagated eastward during the forecast period. Thus, it is unlikely that the operational satellite data will improve forecasts in a data dense region. However, in regions of poor data coverage, the satellite data should have a beneficial effect on numerical forecasts.

Derber, J. C.↗