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A. F. Hasler

The capability of making stereographic observations of clouds and their temporal changes from two simultaneously scanning geosynchronous satellites is a new basic meteorological analysis tool with a broad spectrum of applications. Stereo height measurements, because of their higher horizontal resolution and dependence on only straightforward geometric relationships, represent a big improvement over previously used infrared-based techniques. Verification using high altitude mountain lakes indicates that stereo cloud height accuracies of ± 0.1–0.2 km are possible near reference points of known elevation. The smallest cloud features observed by the present operational geosynchronous satellites (GOES), which have spatial and temporal resolution of 1.0 km and 3 min, can be measured with height accuracies of ± 0.5 km. Absolute stereo height accuracy, far from landmarks, is also about ± 0.5 km if accurate navigation solutions are available for both satellites. Computer remapping of digital image pairs allows the display and height measurement on time sequences of stereo images using an interactive information processing system. Rapid time sequencing of the series of stereo image pairs gives an effective 4-dimensional representation of cloud dynamics. Several interactive techniques have been developed for point measurements of cloud height and cloud height contouring. The stereo observations have been applied to meteorological problems, including: cloud top height contours of intense convective clouds in hurricanes and severe thunderstorms; cloud top and cloud base height estimates for satellite cloud-wind altitude assignment; atmospheric temperature profiles from the combination of stereo heights and infrared cloud top temperatures; determination of cloud emissivity; and finally, comparisons are made between stereo-observed, tropopause-penetrating thunderstorm tops with altitudes up to 17 km and severe weather observations from radar and surface reports. Present stereo coverage using the operational GOES satellites for research demonstrations includes large areas of North and South America and the surrounding oceans. Recommendations are given for operational stereo observations with greater coverage and improved performance employing a third GOES satellite at 105°W.

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C. L. Smith and A. F. Hasler

Abstract

Low-level, ATS-3 satellite wind estimates are compared with values of wind direction and speed interpolated from analyses based on research aircraft observations of a synoptic tropical wave of moderate intensity on 26 July 1969 during BOMFX. The data were stratified according to whether a satellite estimate was positioned in one of three regions; namely, east or west of the wave trough or north of the disturbance center. When cloud and analysis vector magnitude deviations were computed, regional differences became apparent. These differences are attributed to the physical behavior of the cloud targets tracked under the influence of the surrounding large-scale environment.

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A. F. Hasler, W. Shenk, and W. Skillman

Abstract

An initial experiment has been conducted to verify geostationary-satellite-derived cloud motion wind estimates with in situ aircraft wind velocity measurements. The experiment was conducted during December 1972 over the Caribbean Sea with the following aircraft: the National Center for Atmospheric Research (NCAR) Buffalo and Sabreliner, and NASA and U.S. Air Force RB-57F's. The Buffalo and Sabreliner were used for in situ wind velocity measurements and cloud height determinations, and the RB-57F's for precision aerial photogrammetry. Case histories of ½ to 2 h were obtained for 3–10 km diameter cumulus cloud systems on 6 days. Also, one cirrus cloud case was obtained. In most cases the clouds were discrete enough that both the cloud motion and the ambient wind could be measured with the same aircraft Inertial Navigation System (INS). Since the INS drift error is the same for both the cloud motion and wind measurements, the drift error drops out of the relative motion determinations. The magnitude of the vector difference between the cloud motion and the ambient wind at the cloud base averaged 1.2 m s−1. The wind vector at higher levels in the cloud layer differed by about 3 to 5 m s−1 from the cloud motion vector.

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Robert A. Mack, A. F. Hasler, and Robert F. Adler

Abstract

GOES stereoscopy is applied to the study of severe squall line cells. Short interval (3 min) GOES stereoscopic data from the 2–3 May 1979 SESAME case were used to measure cloud top heights of growing storms as a function of time. A one-dimensional cloud model was used to relate the stereoscopically derived cloud top ascent rates to thunderstorm updraft intensity. Results show ascent rates ranging from 4.4 to 7.7 m s−1 for intense cells in a squall line. These results compare well in magnitude with growth rates determined from simultaneous GOES infrared observations and previous estimates of visual cloud and radar echo top growth rates of other thunderstorms.

Detailed stereoscopic cloud top height contour maps of the mature squall line on 2–3 May 1979 were constructed and are discussed here in terms of the small-scale structure and its variability. Results show that for small-scale features (e.g., 5 km diameter tropopause penetrating towers) the short-interval GOES data are not sufficient for studying the life cycle of such features. The stereoscopic height contours are compared to infrared cloud top temperature patterns observed with intense thunderstorms and used to evaluate various theories on the cause of the infrared V-shaped signatures.

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A. F. Hasler, W. E. Shenk, and W. C. Skillman

Abstract

An experiment is in progress to verify geostationary satellite derived cloud motion wind estimates by in situ aircraft wind velocity measurements. One or more low-level aircraft equipped with Inertial Navigation Systems (INS) were used to define the vertical extent and horizontal motion of a cloud and to measure the ambient wind field. A high-level aircraft, also equipped with an INS, took photographs to describe the horizontal extent of the cloud field and to measure cloud motion. The aerial photographs were also used to make a positive identification in the satellite picture of the cloud observed by the low-level aircraft. To date the experiment has been conducted over the tropical oceans in the vicinity of Florida, Puerto Rico, Panama and in the western Gulf of Mexico. A total of 60 h have been spent tracking some 40 tropical cumulus and five cirrus clouds. Results for tropical cumulus clouds indicate excellent agreement between the cloud motion and the wind at cloud base. The magnitude of the vector difference between the cloud motion and the cloud base wind is less than 1.3 m s−1 for 67% of the cases with track lengths of I. h or longer. Similarly, the vector differences between the cloud motion and the wind at sub-cloud (150 m), mid-cloud and cloud-top levels are 1.5, 3.6 and 7.0 m s−1, respectively. The cirrus cloud motions agreed best with the mean wind in the cloud layer with a vector difference of about 1.6 m s−1.

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A. F. Hasler, J. Strong, R. H. Woodward, and H. Pierce

Abstract

A massively parallel processor (MPP) computer has made it practical to do automatic stereo analysis of cloud-top heights from stereoscopic satellite image pairs. The automatic analysis is of equivalent quality to manual analysis while taking several orders of magnitude less time. The height of large-scale structure can be measured more accurately with the automatic analysis, but the height of small-scale towers are underestimated. Simulations using synthetic stereo data show that it is possible to automatically resolve small-scale features (e.g., 4000-m diameter clouds) to about 1500 m in the vertical. Nearly simultaneous image pairs from the GOES and NOAA satellites of hurricanes and tornadic thunderstorm clouds are used to demonstrate automatic analysis on real stereo data. Quality problems with the real stereo data require courser automatic analysis with a minimum scale size of 10 000 m. Higher quality GOES-Next stereoscopic image pairs, expected to be routinely available in the next few years should make useful operational automatic stereo cloud-height measurements practical. Some possible applications of the automatic stereo include severe storm and hurricane nowcasting, aviation forecasting and development of cloud climatologies.

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E. B. Rodgers, R. Mack, and A. F. Hasler

Abstract

Observations of the mean cloud top temperature and height of the eye wall of two tropical cyclones, using GOES infrared and stereoscopic measurements, presented an opportunity to estimate the storm's eye wall tropopause temperature and height. If it is assumed that for a mature tropical cyclone there is little dilution by outside air at the highest eye wall clouds so that the mean-equivalent potential temperature is constant with height from the surface to the cloud top (tropopause), then the mean equivalent potential temperature can be determined knowing the eye wall cloud top temperature and height. With knowledge of the storm's environmental equivalent potential temperature, using either climatological data or rawinsonde measurements together with the satellite derived eye wall equivalent potential temperature, estimation of either the storm's central pressure from the hydrostatic relationship or maximum winds from a cyclostrophic thermal wind relationship becomes possible.

The technique was tested first on Hurricanes Frederic (between 1645 to 2115 GMT 12 September 1979) and Allen (at 2245 GMT on 8 August 1980). Hurricane Frederic's maximum surface wind and central pressure were estimated to be ∼63 m s−1 and 945 mb, which compares well with reconnaissance aircraft measurements (58 m s−1/948 mb) near the time of the GOES observations. Allen's satellite derived maximum wind and central pressure were 78 m s−1 and 915 mb, which again compares favorably with aircraft measurements (73 m s−1/915 mb).

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A. F. Hasler, M. desJardins, and A. J. Negri

The innate capability to perceive 3-dimensional stereo imagery has been exploited to present multidimensional meteorological data fields. Variations on an artificial stereo technique first discussed by Pichel et al. 1973 are used to display single and multispectral images in a vivid and easily assimilated manner. Examples of visible/infrared artificial stereo are given for Hurricane Allen (cover) and for severe thunderstorms on 10 April 1979. Three-dimensional output from a mesoscale model also is presented.

The images may be viewed through the glasses inserted in the February 1981 issue of the Bulletin, with the red lens over the right eye. The images have been produced on the interactive Atmospheric and Oceanographic Information Processing System (AOIPS) at Goddard Space Flight Center.

Stereo presentation is an important aid in understanding meteorological phenomena for operational weather forecasting, research case studies, and model simulations.

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J. Kornfield, A. F. Hasler, K. J. Hanson, and V. E. Suomi

A simple photographic averaging technique using multiple exposures is applied to ESSA III and V computer produced mosaics. Several examples, showing the distribution of clouds, snow, ice and vegetation cover for typical half month periods are presented and discussed. Large scale cloud bands about equatorial dry regions as well as preferred storm tracks are revealed.

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A. F. Hasler, W. C. Skillman, W. E. Shenk, and J. Steranka

Abstract

A 5-year aircraft experiment to verify the quality of satellite cloud winds over oceans using in situ aircraft Inertial Navigation System wind measurements has been completed. The final results show that satellite measured cumulus cloud motions V cloud are very good estimators of the cloud-base wind V CBW (900–950 mb) for trade wind and subtropical high regions. The average magnitude of the vector differences between the cloud motion and the cloud-base wind ranged from 0.9 to 1.7 m s−1 [ 0.9 m s−1 ≤ | VcloudVCBW| ≤1.7 m s−1. For cumulus clouds near frontal regions, the cloud motion agreed best with the mean cloud layer wind V MCLW [|VcloudVMCLW|. For a very limited sample, cirrus cloud motions also most closely followed the mean wind in the cloud layer [|VcloudVMCLW| = 1.7 m s−1].

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