Monographs of the School of Doctoral Studies in Environmental Engineering Doctoral School in Environmental Engineering An investigation of the Ora del Garda wind by means of airborne and surface measurements Lavinia Laiti 2013 Doctoral thesis in Environmental Engineering, XXV cycle Department of Civil, Environmental and Mechanical Engineering, University of Trento Academic year 2011/2012 Supervisor: Dino Zardi, University of Trento On the cover: view of the northern shoreline of Lake Garda from the panoramic trail between Busatte and Tempesta. This thesis is partially based on: Laiti, L., Zardi, D., de Franceschi, M., Rampanelli, G., 2013. Residual kriging analysis of airborne measurements: application to the mapping of atmospheric boundary-layer thermal structures in a mountain valley. Atmos. Sci. Lett. 14, 79-85. Laiti, L., Zardi, D., de Franceschi, M., Rampanelli, G., 2013. Atmospheric boundary-layer structures associated with the Ora del Garda wind in the Alps as revealed from airborne and surface measurements. [submitted to Atmos. Res.] University of Trento Trento, Italy 2013 “Den 13. September, abends. Heute früh um drei Uhr fuhr ich von Torbole weg mit zwei Ruderern. Anfangs war der Wind günstig, daß sie die Segel brauchen konnten. Der Morgen war herrlich, zwar wolkig, doch bei der Dämmerung still. (…) so waren wir schon an Malcesine vorbei, als der Wind sich völlig umkehrte, seinen gewöhnlichen Tagweg nahm und nach Norden zog. Das Rudern half wenig gegen die übermächtige Gewalt, und so mußten wir im Hafen von Malcesine landen.” J. W. Goethe, Italienische Reise (1861) Aknowledgements I would like to thank my supervisor, prof. Dino Zardi, for his support during these years. Thanks also to Dr. Massimiliano de Franceschi for the fruitful discussions, and for providing the data of the field campaign of summer 2001. Thanks to the Trento University Sport Center (CUS Trento) for providing the motorglider, and to the pilot Fabrizio Interlandi for performing the flights. The GIS and Remote Sensing Unit of the Edmund Mach Foundation, the Meteorological Office of the Autonomous Province of Trento (Meteotrentino), the Environmental Protection Agency of the Autonomous Province of Trento (APPA), the National Center for Meteorology and Climatology of the Italian Airforce, the Austrian Aeronautical Meteorological Office (Austro Control) and the Department of Atmospheric Science of the University of Wyoming are kindly acknowledged for providing the data from their surface weather stations and sounding stations. Contents List of Figures ................................................................... ... V List of Tables ................................................. ..................... XV Summary ....................................... ... ............................ .....1 Chapter 1 Introduction ..... .... ..................................... ...................... ........ ..3 1.1 Introduction ........... .............. ................. ................ ... .......... 5 1.2 Motivation and rationale of the thesis....................... ... ..... ...... ........... 6 1.3 Thesis outline........ ..................................................... ...... ...... 8 Chapter 2 The Ora del Garda wind .......... .................... .............. ........ ......... 11 Abstract ........................................... ........................ ....... ... 11 2.1 Introduction ................................... ....... ............................ 13 2.2 Description of the study area........... .......... .................... ......... ... ..17 2.3 The Ora del Garda development....... .... .............................. ........ ..20 2.4 An example of typical Ora del Garda diurnal cycle. ........ ................. ........ 21 2.5 Summary............................................................................27 Chapter 3 Outline of airborne and surface measurements........... ........... ........... ... .....29 Abstract ................................................ ...................... ....... ..... 29 3.1 Introduction ........................................... ................. ........ ..31 3.2 The airborne measurement platform......................................... .... ... 32 3.3 General outline of airborne measurements ......................... ......... ... ..... 33 3.4 24 September 1998 flight (flight #1) ........... ................... ............ ..... 34 3.4.1 Description of the flight........... ................ ................. ........ 34 3.4.2 Weather conditions and surface observations .............. ... ......... ...... 35 3.5 05 August and 01 September 1999 flights (flights #2 and #3) ................ ... ..... 39 3.5.1 Description of the flights................................. .............. .... 39 3.5.2 Weather conditions and surface observations ........... ........... ......... 39 3.6 23 August 2001 flights (flights #4 and #5) ..................... ................. .... 44 3.6.1 Description of the flights........... .... ............ ....................... 44 3.6.2 Weather conditions ........... ............. ............. ............. ...... 46 3.6.3 Ora del Garda diurnal cycle from surface observations. ....... .......... .... 46 I 3.6.3.1 a) Lower Sarca Valley........................ ............. ......... 48 3.6.3.2 b) Lakes Valley .................................. .......... .............51 3.6.3.3 c) Adige Valley south of Trento........... ............ ............. 52 3.6.3.4 d) Adige Valley north of Trento........... ........... ............ ... 52 3.7 Summary........................................... ......... ....... .............. 54 Chapter 4 Methods for the post-processing of airborne data........... ......... ........ ....... 57 Abstract ..................................... ............... .... ............. ................ 57 4.1 Introduction ..... ...... ....................... ............................. ............... 59 4.2 The test-bed dataset .................... ........................ ................... 60 4.2.1 Description of the target area.............. ........... .................. .... 60 4.2.2 Description of the flights.................. ............ ..................... 60 4.3 Correction of the sensor time-lag effect............. .......... ...................... 62 4.3.1 Theoretical framework........... ........... ........... ........... ...... ... 62 4.3.2 Determination of the effective sensor time constant..... ....... ...... ..... ... 66 4.4 The interpolation methods........... .................... ...................... .... 70 4.4.1 Inverse distance methods.....................................................70 4.4.2 Natural neighbor method........... .............. ............ ............ ..71 4.4.3 Residual kriging method........... ................ ........... ........... ..72 4.4.3.1 The pseudo-soundings ........................ ........ ........ .... ...... 72 4.4.3.2 The semivariogram function ..... .... ............... ......... ........... 75 4.5 Comparison of the methods........... ....................... ................... ..77 4.5.1 Cross-validation analysis ........... ................ .................. .... 77 4.5.2 Critical comparison of the interpolated fields........ ........ ............... 82 4.6 Evolution of the ABL thermal structure............................. .......... ...... 88 4.7 Summary ....................................... ............ ........ ............ ........ 90 Chapter 5 Deciphering the dominant vertical structure of the valley atmospheric boundary-layer . ............................................................ ............ .......... ... 93 Abstract ........................................ ................. ....... .......... ... 93 5.1 Introduction ............. .......... .............................................. 95 5.2 24 September 1998 (flight #1) ............. .............................. ....... ... 97 5.3 05 August and 01 September 1999 (flights #2 and #3) .......... ....... .......... ...100 5.3.1 General features of the valley ABL............. ..... .............. ..... ...100 5.3.2 Local features of the valley ABL....................... ................ ...104 5.4 23 August 2001 (flights #4 and #5) ............. ........ ..................... .....104 5.4.1 ABL structure in the lower Sarca Valley and Lakes Valley........... ... ..... 107 5.4.2 ABL structure and evolution in the interaction area............. ...... ..... 108 II 5.5 Summary.................. ................................................. .....110 Chapter 6 Deciphering the fine-scale structure of the valley atmospheric boundary-layer.... 113 Abstract.............. .................................................................. ..... 113 6.1 Introduction ......... ........................................... .... .......... ...115 6.2 24 September 1998 (flight #1) ............. ..... .......................... ..... ...117 6.3 05 August and 01 September 1999 (flights #2 and #3). ..... .......... ........ ..... 121 6.3.1 Lower Sarca Valley - Lake Garda shoreline area............. ........... ...121 6.3.2 Lakes Valley - Cavedine Lake area ............. .......... .............. ... 123 6.3.3 Lakes Valley - Terlago saddle area......................... ... .......... ..125 6.3.4 Adige Valley - interaction area ............. ......... .................. ...127 6.4 23 August 2001 (flights #4 and #5) ............. ... ..................... ....... ...130 6.4.1 Lower Sarca Valley........ ............................