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Cloud Microphysics Studies for Texas Hiplex 1979

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Cloud Microphysics Studies for Texas Hiplex 1979 PRELIMINARY CLOUD MICROPHYSICS STUDIES FOR TEXAS HIPLEX 1979 LP-124 TWDB CONTRACT NOS. 14-90026 AND 14-00003 Prepared by: DEPARTMENT OF METEOROLOGY COLLEGE OF GEOSCIENCES TEXAS A&M UNIVERSITY COLLEGE STATION, TEXAS Prepared for: TEXAS DEPARTMENT OF WATER RESOURCES AUSTIN, TEXAS Funded by: DEPARTMENT OF THE INTERIOR, WATER AND POWER RESOURCES SERVICE TEXAS DEPARTMENT OF WATER RESOURCES APRIL 1980 M8-H0O (3-78) Buruau of Reclamation TECHNICAL REPORT STANDARD TITLE PAGE 1. REPORT NO. 3. RECIPIENT'S CATALOG NO. 4. TITLE AND SUBTITLE S. REPORT OATE Preliminary Cloud Microphysics Studies March, 1980 for Texas HIPLEX 1979 6. PERFORMING ORGANIZATION CODE 330 7. AUTHORIS) 8. PERFORMING ORGANIZATION REPORT NO. Alexis B. Long LP-124 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO. Texas Department of Water Resources 5540 P.O. Box 13087, Capitol Station 11. CONTRACT OR GRANT NO. Austin, TX 78711 14-06-D-7587 13. TYPE OF REPORT AND PERIOD COVEREO 12. SPONSORING AGENCY NAME AND ADDRESS Office of Atmospheric Resources Management T echnical Water and Power Resources Service Building 67, Denver Federal Center 14. SPONSORING AGENCY CODE Denver, Colorado 80225 15. SUPPLEMENTARY NOTES 16. ABSTRACT Cloud microphysics studies made in connection with Texas HIPLEX 1979 are described. Any results, however, must be regarded as preliminary and sub ject to revision based on further work. The objective is to determine important natural precipitation mechanisms in summertime convective clouds in the Big Spring, Texas area. Studies are based on data collected by twq instrumented aircraft. Operational procedures used for collecting data are described. Rules used for selecting clouds microphysically suitable for study are listed. A preliminary analysis of a cloud sampled on June 4 re veals a possible example of ice multiplication. Analysis of data collected on July 17 within and beneath a mesoscale convective system shows that when precipitation falls through subcloud air its temperature is decreased and dewpoint increased. From information on the development of ice and pre cipitation in seven clouds and from estimates of the precipitation from each cloud, a preliminary conclusion is drawn that the ice process is necessary for significant precipitation to occur. 17. m:y WOHDS ANO DOCUMENT ANALYSIS o. DESCRIPTORS-- cloud microphysics; ice multiplication; convective clouds; precipitation mechanisms; rain enhancement; condensation nuclei b. identifiers-- Big Spring, Texas/ Texas High Plains Cooperative Program (HIPLEX) c. CuSA 1 I F ie HI/Group COV/RR: 18. DISTRIBUTION STATEMENT 19. SECURITY CLASS 21. NO. OF PAGES (THIS REPORT) Available from the National Technical Information Service, Operations UNCLASSIFIED Division. Springfield, Virginia 22161. 20. SECURITY CLASS 22. PRICE (This page) UNCLASSIFIED GPO 645- 630 PRELIMINARY CLOUD MICROPHYSICS STUDIES FOR TEXAS HIPLEX 1979 Alexis B. Long Department of Meteorology College of Geosciences Texas ASM University College Station, Texas 77843 February 1980 Technical Report TDWR Contracts Nos. 14-90026 and 14-00003 Availability Unlimited Prepared for Texas Department of Water Resources Austin, Texas Funded by Department of the Interior, Water and Power Resources Service, and the State of Texas through the Texas Department of Water Resources ABSTRACT The first cloud microphysics studies made by Texas A&M University in connection with Texas HIPLEX are described. The studies are only beginning, and any results must be regarded as preliminary and subject to revision on the basis of further work. The aim of the studies is to determine the important natural precipitation mechanisms in summertime convective clouds in the Big Spring, Texas area. The studies are based on data collected by two instrumented aircraft in 1979. Operational procedures used for collecting data are described. Rules used for selecting clouds micrpphysically suitable for study are listed. The selection rules were met in over half the clouds, but for a fraction of the clouds either the top temperature was too low, the initial concentra tion of ice particles was too high, or precipitation was already under way. A preliminary analysis based on incomplete data of a cloud sampled on 4 June 1979 reveals a possible example of ice multiplication. Analysis of data collected on 17 July 1979 within and beneath a mesoscale convective system shows that when precipitation falls through subcloud air its temperature is decreased and dewpoint increased. This may be an example of the wet-bulb process operating within subcloud air or an example of penetration of potentially cold downdraft air into the subcloud region. From information on the development of ice and precipitation in seven clouds and from estimates of the precipitation from each cloud, a preliminary conclusion is drawn that the ice process is necessary for significant precipitation to occur. This conclusion strictly applies only to the clouds studied. li TABLE OF CONTENTS • Page ABSTRACT ii LIST OF FIGURES iv LIST OF TABLES vi 1. INTRODUCTION 1 2. SCIENTIFIC APPROACH 3 3. DATA COLLECTION 12 4. ANALYSIS OF CLOUD SELECTION 25 5. DATA PROCESSING 32 6. DATA ANALYSES 33 a. 4 June 1979 (1) 34 b. 17 July 1979 44 c. Precipitation mechanisms 53 7. SUMMARY 62 8. FUTURE PLANS 64 REFERENCES 65 APPENDIX 66 in LIST OF FIGURES Page Figure Flow diagram of the major types of cloud and precipi tation elements and of the physical processes through which they originate, grow, and interact. (Similar to diagram of Braham and Squires (1974).) See text for discussion 4 Flight pattern for sampling an isolated cumulus congestus cloud in 1979 Texas HIPLEX field program. The three aircraft flew back and forth through a cloud along a straight line with reciprocal turns at each end. Temperature levels are those attempted but were not always achieved. See text for discussion 16 Flight pattern for sampling a growing turret in a convective complex in 1979 Texas HIPLEX field program. The three aircraft flew back and forth through a turret along a straight line with reciprocal turns at each end. Temperature levels are those attempted but were not always achieved. See text for discussion 17 Flight track of MRI Navajo through cloud A of HIPLEX Mission 1 on 4 June 1979 (1). Solid line shows part of flight track in cloud. Dashed line shows ou£-of-cloud flight track made up of straight line segments between 30-sec positions of the aircraft 35 MRI Navajo data for pass 1 through cloud A of HIPLEX mission 1 on 4 June 1979 (1). One-second values are shown of vertical velocity, ambient air temperature, cloud liquid water content, cloud droplet concentration, precipitation water content, precipitation particle concentration, and ice particle concentration. Time increases from left to right 36 Same as Fig. 5 but for pass 2. Time increases from right to left so data have same approximate geographical orientation as those in Fig. 5 39 Same as Fig. 5 but for pass 3. Time increases from left to right so data have same approximate geographical orientation as those in Figs. 5 and 6. 41 Same as Fig. 5 but for pass 4. Time increases from right to left so data have same approximate geographical orientation as those in Figs. 5, 6, and 7 42 iv LIST OF FIGURES (Continued) Figure Page 9 MRI Navajo flight track for mapping mesoscale temper ature, dewpoint, and precipitation fields from 2103 to 2153 GMT on 17 July 1979. Plotted at 1 min intervals are ambient air temperature (upper figure) and dewpoint (lower figure). Flight level was approxi mately 3.2 km (10,500 ft) MSL 45 10 Same as Fig. 9 except for precipitation water content (g m~3) 47 11 One-second values of MRI Navajo vertical velocity and precipitation water content, plotted every 5 seconds. 48 12 p-Navajo flight track for mapping of mesoscale temper ature and dewpoint fields for 2035 to 2105 GMT on 17 July 1979. Plotted at 1-minute intervals are ambient air temperature (upper figure) and dewpoint (lower figure). Also plotted are comments on, vertical velocity, precipitation, and other items as observed and recorded by the TAMU flight observer. Flight level was 1.2 km (4,000 ft) MSL 49 13 Same as Fig. 12 but for 2105 to 2148 GMT on 17 July 1979 51 14 Same as Fig. 12 but for 2148 to 2216 GMT on 17 July 1979 52 15 Ice multiplication boundary as determined by cloud droplet concentration at cloud base and cloud base temperature (after Mossop (1978)) 60 LIST OF TABLES Table Page 1 Variables measured and recorded by MRI Navajo in 1979 Texas HIPLEX field program . 13 2 Variables measured and recorded by p-Navajo in 1979 Texas HIPLEX field program 14 3 Cloud selection rules for 1979 HIPLEX missions .... 18 4 Summary of aircraft data-gathering missions in 1979 Texas HIPLEX field program 20 5 Summary of cloud microphysics missions in the 1979 Texas HIPLEX field program 21 6 Types of cloud selected in 1979 HIPLEX missions ... 26 7 Elapsed time from cloud selection to first MRI Navajo pass and to cloud seeding 27 8 Initial states of selected clouds 29 9 Development of and total precipitation for clouds sampled and treated in 1979 HIPLEX missions 54 10 Components of total precipitation for sampled clouds . 58 VI 1. INTRODUCTION The overall objectives of the Texas A&M University (TAMU) cloud microphysics studies are: 1) to understand the important natural precipitation mechanisms in convective clouds in the Texas HIPLEX study region, and 2) to formulate and test rain enhancement hypotheses appropriate to these clouds. Some progress toward Objective 1 is necessary before Objective 2 can be pursued. This report focusses on Objective 1. Progress to date is not sufficient to support a statement on appropriate rain enhancement hypotheses for convective clouds in the Texas HIPLEX study region. The cloud microphysics studies presented in this report are the first to be made by Texas A&M University in connection with Texas HIPLEX.
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