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N a S a C O N T R a C T O R Report NASACONTRACTOR REPORT 4 M Q a Prepared by TEXAS A&M UNIVERSITY College Station, Texas for Flight Research Center NATIONALAERONAUTICS AND 5PACE ADMINISTRATION WASHINGTON, D. C. e JULY 1971 TECH LIBRARY KAFB, NM lrnl1lRllnllllrnll~l~lllll 0061128 1, Report No. 2. Government Accession No. 3. Recipient'sCatalog No. NASA CR-1878 4. Title and Subtitle AN INVESTIGATION OF THE RELATIONSHIPS BETWEEN 5. Report Date MOUNTAIN-WAVE CONDITIONS AND CLEAR AIR TURBULENCE ENCOUNTERED BY THE XB-70 AIRPLANEIN THE STRATOSPHERE pi?g?rganization Code 7. Author(s) 8. Performing Organization Report No. H-679 Thomas P. Incrocci and James R. Scoggins ~ 10. Work Unit No. 9. Performing Organization Name and Address Texas A&M University College Station, Texas 11. Contract or Grant No. NGR-44-001-081 13. Type of Report and Period Covered ~ 12. Sponsoring AgencyName and Address National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, D. C. 20546 15. Supplementary Notes 16. Abstract The data from 36 XB-70 flights conducted over the mountainous regions of the western United States together with rawinsonde data were used to investigate relationships between conditions favorable for mountain waves and clear air turbulence. Profiles for the Scorer parameter and the gradient Richardson number were evaluated from an eight-level model. The Scorer parameter and the gradient Richardson number profiles were computed from the rawinsonde dataon those days when the XB-70 flew, and these results compared to the model profiles and related to the reported turbulence. Ascent rate profiles of rawinsonde balloons were analyzed from which the presence of mountain or lee waves was inferred. From the results of this investigation, objective methods were developed for forecasting the occurrence or non-occurrence of turbulence in the stratosphere due to mountain waves. 17. Key(Suggested Words Author(s) by 1 18. Distribution Statement High-altitude turbulence Mountain-wave conditions Rawinsonde Unclassified - Unlimited Ascent rate I ~ 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price' Unclassified Unclassified - 34 $3.00 For sale by the National Technical InformationService, Springfield, Virginia 22151 .. .. , . .. .. ~ I TABLE OF CONTENTS PAGE TABLE OF CONTENTS ........................... iii LIST OF TABLES ............................ V LIST OF FIGURES ............................ vi SUMMARY ................................ 1 INTRODUCTION ............................. 1 BACKGROUND OF THE PROBLEM ....................... 3 The TheoryofMountain Waves .................... 3 Mountain Waves and Clear Air Turbulence (CAT) ............ 4 The Vertical Propagation and Transfer ofEnergy of Mountain Waves intothe Stratosphere ............... 5 The Influence of Wind and Stability on Profiles of theScorer Parameter and theRichardson Number .......... 6 ANALYSES OF DATA ........................... 10 GroupingofData .......................... 10 Aircraft ............................. 10 Meteorological .......................... 13 AnalyticalResults ......................... 13 The normal wind component at 700 mb ................ 13 The 700- to 500-mb lapserate oftemperature ........... 19 The gradient and advectionof stability .............. 19 Scorerparameter and Richardson number profiles .......... 20 Vertical wind shear ........................ 25 Evidence of the presence of mountain waves from the variation in ascentrate ofrawinsonde balloons .......... 26 iii ........ ". ~ TABLE OF CONTENTS (CONTINUED) PAGE FORECASTING CAT IN THE STRATOSPHERE FROM CONDITIONS IN THE TROPOSPHERE ............................ 30 CONCLUDING REMARKS ......................... 31 REFERENCES ............................. 33 iV LIST OFTABLES TABLE TITLE PAGE I PROFILESOF WIND AND TEMPERATURE FOR MODEL ATBDSPHERES ......................... 7 I1 SYNOPTIC FEATURES AT 700 MJ3 AND THE AVERAGE VALUES ALONG THE FLIGHT TRACK FOR THE 700- TO 500"B LAPSE RATE OF TEMPERATURERELATED TO THE CONDITIONS IN THESTRATOSPHERE REPORTED BY THE XB-70 .................... 14 I11 THE HORIZONTALGRADIENT OF THE 700- TO 500"B LAPSE RATE OF TEMPERATURE RELATED TO CONDITIONS AT 700 MB AND TURBULENCE REPORTED IN THE STRATOSPHERE BY THE XB-70 .................. 20 IV TURBULENCE OR POTENTIAL TURBULENCE CONDITIONS IN THE STRATOSPHERE RETATED TO THE MINIMUM VALUEOF THE AVERAGE PROFILE OF L2 .................. 24 V THEV RATIO OF THE FIRST TO THE SECONDTERM OF THE SCORER PARAMETER VERSUS THE REPORTED CONDITIONS IN THE STRATOSPHEREAM)TROPOSPHERE ............. 25 VI INDICATIONOF THE PRESENCE OR ABSENCE OF MOUNTAIN WAVESFROM THE VARIATION IN ASCENT RATEOF THE RAWINSONDEBALLOON ..................... 28 VII THEAVERAGE MAGNITUDE ANDRANGE OF NEAR-MAXIMUM VARIATIONS IN ASCENT RATEOF RAWINSONDE BALLOONS FOR EACHCATEGORY GIVEN IN TABLE VI ............. 29 V ", ............. .- LIST OF FIGURES FIGURE TITLE PAGE 1 The profilesof L2 forthe strong wind profilein combinationwith selected temperature profiles ........ 7 2 The profilesof L2 forthe light wind profilein combinationwith selected temperature profiles ........ 8 3 The profiles of Ri forthe strong wind profilein combinationwith selected temperature profiles ........ 9 4 The profiles of Ri forthe light wind profilein combinationwith selected temperature profiles ........ 9 5 Examples of theturbulence data reported by the XB-70 aircraftin the stratosphere (after Ehernberger, ref. 1) ... 11 6 Rawinsonde stationsin the western United States and the prevailing wind directions favorable for the developmentof extensive mountain-wave activity in the surroundingareas (wind directions taken from Harrison andSowa, ref. 21) ...................... 13 7 Mid-troposphericconditions for 1200 GMT on 19 March 1966 ........................ 15 8 Mid-troposphericconditions for 1200 GMT on 4 March 1965 ......................... 16 9 Mid-troposphericconditions for 1200 GMT on 27 July 1965 ......................... 17 10 Mid-troposphericconditions for 1200 GMIl on 16October1965 ........................ 18 11 Eightaverage profiles of L2 when the normal windcomponent at the mountain crests was at least 10 m sec-l and conditions reported in the stratosphere by the XB-70 were classified as turbulencecases ....................... 21 12 Average profiles of Ri which correspond tothe first four profiles of L~ infigure 11 ................. 21 13 Average profiles of Ri which correspond tothe last four profilesof L2 infigure 11 ................. 22 vi LIST OF FIGURES (CONTINUED) FIGURE TITLE PAGE 14 Average profiles of L2 for specific conditions at 700 mb and inthe stratosphere: (1) A closed low at 700' mb within 5 deg of latitude of the flight track of the XB-70 and classified as a turbulence case; (2) the windcomponent normal to the mountain tops less than 10 m sec'l and classified as a turbu- lencecase; (3) the windcomponent normal to the mountaintops less than 10 m sec'l and classified as a no-turbulencecase .................. 22 15 The average profiles of Ri for the cases and conditions specified for the corresponding profiles of L2 in figure 14. ......................... 23 16 Theminimum value in the middle or upper troposphere of the average profiles of L2 and Ri for those cases with actual and potential wind components of at least 10 m sec'lnormal tothe mountain tops and for all closed-low areas within 5 degof latitude of the flight track of the XB-70. (NOTE: The minimum wind criterion was notconsidered inthe closed-lowcases.) ........ 23 17 The minimum value in the middle or upper troposphere of the average profiles of L2 and Ri for those cases with wind components less than10 m sec-' normal to the mountaintops. (NOTE: Closed-lowcases are not consid- ered inthis figure.) ................... 24 18 Examples of the ascent rate of rawinsondeballoons indicative of the presence ofmountain waves (21 April 1965) and theabsence of such waves (28 April1965). Thesmooth lines represent average ascent rate profiles drawn by eye. 27 vii I AN INVESTIGATION OF THE RELATIONSHIPS BETWEEN MOUNTAIN-WAVE CONDITIONS AND CLEAR AIR TURBULENCE ENCOUNTERED BY THE XB-70 AIRPLANE IN THE STRATOSPHERE By Thomas P. Incrocci and James R. Scoggins Texas A&M University SUMMARY The data from36 XB-70 flights conducted over the mountainous regions of the western United States together with rawinsonde data were used to investigate relationships between conditions favorable for mountain waves and clear air turbulence. Profiles for the Scorer parameter and the gradient Richardson num- ber were evaluated from an eight-level model.The Scorer parameter and the gradient Richardson number profiles were computed from the rawinsonde data on those days when theXB-70 flew, and these results compared to the model profiles and related to the reported turbulence. Ascent rate profilesof rawinsonde balloons were analyzed from which the presence of mountain or lee waves was inferred. From the results of this investigation, objective methods were devel- oped for forecasting the occurrence or non-occurrenceof turbulence in the stratosphere due to mountain waves. INTRODUCTION The problem of stratospheric turbulence was vividly brought to light when the supersonic XB-70 airplane made numerous test flightsin the western United States during 1965 and 1966 (ref. 1). With aviation on the threshold of routine supersonic flight in the stratosphere, further investigationof this phenomenon is justified on the basis of safety and passenger comfort. Extensive analyses have been accomplished by Scoggins (ref.2) to
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