Search Results

You are looking at 1 - 10 of 12 items for

  • Author or Editor: Thomas M. Whittaker x
  • All content x
Clear All Modify Search
Thomas M. Whittaker

Abstract

A simple technique for automated (computer-generated) streamline analysis is presented. Descriptions of the algorithms utilized to perform this task are made. Finally, examples are presented which illustrate the ability of the method to represent neutral points (singularities) in the analysis method.

Full access
Thomas L. Koehler and Linda M. Whittaker

Abstract

Available potential energy and kinetic energy distributions for the Northern Hemisphere computed from the FGGE Level IIIa analyses produced at the National Meteorological Center (NMC) and the Level IIIb analyses prepared at the European Centre for Medium Range Weather Forecasting (ECMWF) are presented for a two‐week period 14–27 February 1979.

The most significant difference between the two datasets appear in the eddy components, where the hemispheric ECMWF values are smaller than the NMC values. This difference is found at almost every latitude in the APE distributions and in tropical and polar latitudes in the KE distributions.

Vertical cross sections and 250 mb height patterns for three individual days show smoother and weaker short wave features over the oceans in the ECMWF analyses. Jet streak maxima at 250 mb tended to be stronger in the NMC analyses. These results are consistent with those from previous studies which noted smaller energy values in the ECMWF analyses compared to NMC and GFDL analyses.

Full access
Frank S. Sechrist and Thomas M. Whittaker

Abstract

A Man Computer Interactive Data Access System (McIDAS) has been used to great advantage in the monitoring and processing of weather data on a real-time basis. In particular, McIDAS facilitated the timely acquisition of data for the study of a Midwest cyclone which was characterized by a well-defined jet streak aloft. Moreover, study of this jet streak revealed patterns of ageostrophic motion and divergence which agree well with the theory of jet streak vertical circulations. Previously, there had been only limited documentation of these patterns using an actual case study.

The most striking results of this study were as follows:

1).Machine computation of synoptic-scale ageostrophic motions and divergence patterns can beaccomplished with a high degree of reliability and consistency.

2)The weather over large areas of the United States can be affected by a single, well-definedjet streak.

3)Significant research can now be accomplished on a near real-time basis. Systems such as McIDAS

hold the promise of generating frequent and exhaustive diagnostic studies of the real atmosphere ina very short time frame.

4)Comparisons with independent data show obvious connections between the jet streak verticalcirculations and synoptic-scale cloud and weather patterns.

Full access
Thomas M. Whittaker and Ralph A. Petersen

Abstract

Overlapping second-order Lagrangian polynomials are used to construct cross-sectional isentropic analyses from upper air sounding observations. Estimates of geostrophic winds are obtained through the thermal wind relationship. Thermal information is also combined with normal components of the observed wind to obtain a thermally enhanced, observed wind analysis. Results using these techniques are presented and compared with a previous objective analysis technique developed by Shapiro and Hastings (1973). Examination of the results indicates the applicability of the techniques both for operational and research purposes.

Full access
Lyle H. Horn, Thomas L. Koehler, and Linda M. Whittaker

Abstract

Available potential energy (APE) calculations are used to evaluate the influence of the FGGE satellite observing system during the first Special Observing Period (SOP-1). Two datasets consisting of the Goddard Laboratory for Atmospheres analyses are used: the complete FGGE IIIb set which has incorporated satellite soundings and a NOSAT set which incorporates only conventional data. The major portion of the study uses the exact (isentropic) formulation of APE; however, some introductory comparisons are made with the approximate (isobaric) form. Time series of the daily total APE values show the NOSAT set yielding slightly larger values in both APE formulations, with the approximate form zonal component exhibiting the largest difference, An examination of the average eddy APE (exact form) contributions from 4° latitude rings reveals that in the Southern Hemisphere middle latitudes the NOSAT values are larger than the FFGE values; however in the Northern Hemisphere the differences are negligible.

Analyses of the vertically integrated gridpoint contributions to the eddy APE reveal that the exact form of the APE clearly defines cyclone scale features. The gridpoint distributions show only minor differences between the Northern Hemisphere FGGE and NOSAT analyses, but substantial differences exist in the Southern Hemisphere where the satellite soundings apparently add detail to the FGGE set by locating the trough and ridge systems associated with cyclones more accurately. However, the weaker thermal gradients obtained from satellite soundings tend to yield smaller eddy APE values. Temporal standard deviations of the gridpoint contributions to the eddy APE are closely related to extratropical cyclone tracks. Again there is essentially no difference in the two datasets in the Northern Hemisphere, but differences exist in the Southern Hemisphere.

Finally an analysis of the FGGE-NOSAT temperature differences in vertical cross sections along 54°N and 54°S show larger differences in the Southern Hemisphere. Some of the differences clearly propagate eastward during a three-day period. In some areas large differences of one sign overlay large differences of the opposite sign implying significant differences in static stability between the two sets.

Full access
Lyle H. Horn, Ralph A. Petersen, and Thomas M. Whittaker

Abstract

A 23–24 February 1975 case study is made comparing the results achieved using Nimbus 5 satellite temperature, profiles with those obtained from radiosonde data and the initial hour data of the Limited Area Fine Mesh (LFM) model of the National Meteorological Center. An objective analysis technique is used to construct and analyze isotropic cross sections through an intense baroclinic zone. A cross section based on 1700 GMT Nimbus 5 soundings is compared with those based on 1200 and 0000 GMT radiosonde and LFM data. Geostrophic shear calculations are used to compare the thermal gradients for various isobaric layers obtained from the three data acts. The Nimbus 5 results show somewhat less detail than those based on the radiosonde data, but wore than those obtained from the LPM data. Comparisons of the mean temperature in various isobaric layers for the three time periods indicate that the 1700 GMT Nimbus 5 data appear to be consistent with the changing synoptic pattern. Estimates of the wind components normal to the cross sections are obtained using 1) the geostrophic wind calculated from Nimbus 5 data, 2) the observed winds which are enhanced by the geostrophic shear obtained from the radiosonde data, and 3) the initial-hour LFM winds. The wind estimates also indicate that the Nimbus 5 data provide results which agree with the evolving synoptic situation. In general, the results suggest that the insertion into numerical models of satellite-derived mean thermal gradients calculated for 100–200 mb thick layers, rather than mean temperatures, may facilitate the use of satellite soundings.

Full access
Rajul E. Pandya, David R. Smith, Donna J. Charlevoix, Genene M. Fisher, Shirley T. Murillo, Kathleen A. Murphy, Diane M. Stanitski, and Thomas M. Whittaker
Full access
Steven M. Lazarus, Jennifer M. Collins, Martin A. Baxter, Anne Case Hanks, Thomas M. Whittaker, Kevin R. Tyle, Stefan F. Cecelski, Bart Geerts, and Mohan K. Ramamurthy
Full access
Matthew A. Lazzara, John M. Benson, Robert J. Fox, Denise J. Laitsch, Joseph P. Rueden, David A. Santek, Delores M. Wade, Thomas M. Whittaker, and J. T. Young

On 12 October 1998, it was the 25th anniversary of the Man computer Interactive Data Access System (McIDAS). On that date in 1973, McIDAS was first used operationally by scientists as a tool for data analysis. Over the last 25 years, McIDAS has undergone numerous architectural changes in an effort to keep pace with changing technology. In its early years, significant technological breakthroughs were required to achieve the functionality needed by atmospheric scientists. Today McIDAS is challenged by new Internet-based approaches to data access and data display. The history and impact of McIDAS, along with some of the lessons learned, are presented here.

Full access
Rajul E. Pandya, David R. Smith, Donna J. Charlevoix, Wayne Hart, Marianne J. Hayes, Shirley T. Murillo, Kathleen A. Murphy, Diane M. Stanitski, and Thomas M. Whittaker
Full access