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Thomas L. Koehler

Abstract

Evaluations of limb-corrected brightness temperatures computed by NESDIS from TIROS-N MSU observed brightness temperatures are presented. Observed brightness temperatures both before and after limb correction are compared to simulated brightness temperatures derived from conventional radiosonde measurements.

Results suggest a left-to-right bias in the limb-corrected MSU data, with the left side colder than the right side. The uncorrected MSU brightness temperatures can be more accurately simulated than those available after the limb correction technique is applied. Incorporating the actual MSU antenna patterns into the simulations removes most of the scan angle dependence in the bias differences.

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Thomas L. Koehler

Abstract

This study employs cloud-to-ground (CG) lightning flash data from the U.S. National Lightning Detection Network (NLDN) to examine temporal and spatial distributions of lightning flash and thunderstorm day (TD) occurrences over the contiguous United States from 1993 to 2018. TD distributions are estimated from NLDN CG flashes using 4 thunder audibility approximations: 5 and 10 nautical mile (n mi; 1 n mi = 1.852 km) audibility ranges, and minima of 1 and 2 flashes within the audibility range. The 26-yr period examined is longer than previous studies using NLDN data, and the TD results can be compared directly to climatologies derived from surface weather observations dating back to the late 1890s. Results based on the abundant NLDN data avoid limitations introduced by the coarse horizontal resolution of surface observations inherent in pre-NLDN TD climatologies. Annual mean flash density and annual and monthly mean TD distributions are derived from almost 568 million NLDN CG flashes. A mean annual maximum of more than 16 flashes km−2 is found near Tampa, Florida. The mean annual TD maximum of 113 days (from at least 2 flashes within 10 n mi) occurs in southern Florida. Regions exceeding 70 TDs are found from eastern Texas eastward into Florida, and over the southern Rocky Mountains. Large positive deviations from the mean number of TDs extend from Texas northwestward into Colorado during 2003–07, followed by large negative deviations over the same region during 2008–12. Both deviation patterns are similar to expected summertime precipitation anomaly patterns over the United States during El Niño and La Niña years, respectively.

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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.

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Casey E. Davenport, Christian S. Wohlwend, and Thomas L. Koehler

Abstract

Education research has shown that there is often a disconnect between what instructors teach and what students actually comprehend. Much of this disconnect stems from students’ previous conceptions of the subject that often remain steadfast despite instruction. The field of meteorology is particularly susceptible to misconceptions as a result of the years of personal experience students have with weather before instruction. Consequently, it is often challenging for students to accurately integrate course material with their observations and personal explanations. A longitudinal assessment exam of the meteorology program at the U.S. Air Force Academy revealed that misconceptions of fundamental, introductory content can propagate through years of instruction, potentially impeding deeper understanding of advanced topics and hindering attainment of professional certifications. Thus, it is clear that such misconceptions must be identified and corrected early. This manuscript describes the development of the Fundamentals in Meteorology Inventory (FMI), a multiple-choice assessment exam designed to identify the common misconceptions of fundamental topics covered in introductory meteorology courses. In developing the FMI, care was taken to avoid complex vocabulary and to include plausible distractors identified by meteorology faculty members. Question topics include clouds and precipitation, wind, fronts and air masses, temperature, stability, severe weather, and climate. Applications of the exam for the meteorology community are discussed, including identifying common meteorology misconceptions, assessing student understanding, measuring teaching effectiveness, and diagnosing areas for improvement in introductory meteorology courses. Future work to be completed to ensure the efficacy of the FMI will also be acknowledged.

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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.

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Thomas L. Koehler, John C. Derber, Brian D. Schmidt, and Lyle H. Horn

Abstract

Evaluations of operational TIROS-N and NOAA-6 temperature soundings over North America are presented for an early January 1980 period one month after completion of the First GARP Global Experiment. In addition to collocated comparisons, synoptic analyses derived only from satellite data and model forecasts initialized from these analyses are compared with those obtained from conventional data. The collocated results, similar to those presented by Phillips et al. (1979) and Schlatter (1981) from TIROS-N soundings, show maximum sounding errors new the surface and tropopause. The analysis comparisons further illustrate that thermal gradients inferred from satellite soundings are too weak, with NOAA-6 gradients slightly weaker than TIROS-N gradients. Difference fields between satellite and conventional thickness analyses propagate eastward with the synoptic patterns, strongly suggesting a correlation of satellite sounding errors to synoptic patterns. These anomalies are also retained in model forecasts started from satellite analyses. These results stress the importance of properly defining the error characteristics of satellite soundings before incorporating them into analysis-forecast systems.

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Thomas L. Koehler, Charles J. Seman, James P. Nelson III, and Lyle H. Horn

Abstract

Alternatives to the retrieval techniques applied by NESDIS operations to derive the FGGF Level IIa soundings are examined. A physical iterative retrieval technique is compared to the operational statistical method, and the influence of using higher resolution subsets of the original infrared observations is examined. These alternatives are evaluated using TIROS-N observations from a January 1980 period over the conventional data-rich region of the United States. The evaluations involve colocation statistics and 700–300 mb thickness difference fields. The initial tests using operational (9 × 7 HIRS/2 fields of view) resolution show that the physical iterative retrieval makes substantial corrections to climatological first guesses, but only minor corrections to a first guess based on the operational soundings. Colocation statistics and 700–300 mb thickness difference fields indicate that the physical retrieval method does not offer significant improvements over the FGGE operational soundings. As in the operational soundings, there is a tendency for the sounding errors to be synoptically correlated with troughs ton warm and ridges too cold, thus reducing thermal gradients.

In an attempt to improve the thermal gradient information, the physical iterative method (using the operational sounding first guess) was also employed to retrieve soundings based on radiances obtained from higher (3 × 3 HIRS/2 fields of view) resolution. Four different subsets of the 3 × 3 sounding sets were studied with varying horizontal resolutions and with and without manual editing. Each set shows some improvement over the 9 × 7 retrievals, particularly through a reduction of the bias in the low and midtroposphere. Further analysis reveals that the improvement in retrieval accuracy is sounding-type dependent, with only the 3 × 3 clear retrievals showing definite improvement over 9 × 7 retrievals for this case. The 700–300 mb thickness fields obtained from the 3 × 3 FOV soundings also show synoptically correlated errors.

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Albert J. Williams 3rd, John S. Tochko, Richard L. Koehler, William D. Grant, Thomas F. Gross, and Christopher V. R. Dunn

Abstract

A vertical array of acoustic current meters measures the vector flow field in the lowest 5 m of the oceanic boundary layer. By resolving the velocity to 0.03 cm s−1 over 15 cm paths, it samples the dominant turbulent eddies responsible for Reynolds stress to within 50 cm of the bottom. Profiles through the inner boundary layer, from six sensor pods, of velocity, turbulent kinetic energy, and Reynolds stress can be recorded for up 10 four months with a 2 Hz sample rate and 20 min averaging interval. We can study flow structure and spectra from as many as four event-triggered recordings of unaveraged samples, each lasting one hour, during periods of intense sediment transport. Acoustic transducer multiplexing permits 24 axes to be interfaced to a single receiving circuit. Electrical reversal of transducers in each axis eliminates zero drift. A deep-sea tripod supports the sensor array rigidly with minimum flow disturbance, yet releases on command for free vehicle recovery.

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