Alma Mater Studiorum · Universita` di Bologna Scuola di Scienze Corso di Laurea Magistrale in Fisica The Atmospheric Stable Boundary Layer: Data Analysis and Comparison with Similarity Theories Relatore: Presentata da: Prof. Francesco Tampieri Matteo Michelotti Sessione II Anno Accademico 2012/2013 2 Contents Sommario . .9 Abstract . 10 1 Introduction 11 1.1 The Atmosphere . 11 1.1.1 Troposphere . 12 1.1.2 Stratosphere . 12 1.1.3 Mesosphere . 13 1.1.4 Thermosphere . 13 1.2 Planetary Boundary Layer . 14 1.3 Static Stability . 16 1.4 Turbulence and Turbulent Motion . 18 1.4.1 Turbulent Kinetic Energy . 23 1.4.2 Turbulent Fluxes . 23 1.5 Equations and Closure Problem . 26 1.5.1 Equations for the istantaneous quantities . 26 1.5.2 Equation for the first moments . 29 1.5.3 Equation for the second moments . 30 1.5.4 Closure problem . 33 1.6 Similarity Theory . 34 1.6.1 The Buckinghan Theorem . 35 1.6.2 The Monin-Obukhov Similarity Theory (MOST) . 36 1.6.3 Similarity Functions for the wind Shear and Profile . 38 1.6.4 Similarity Functions for the Temperature Gradient and Profile . 38 3 4 CONTENTS 1.6.5 Richardson Numbers . 39 2 Data Analysis 41 2.1 Origin of the data: SABLES98 . 41 2.2 Surface Roughness Length z0 .................. 44 2.3 Vertical structure of the SBL . 46 2.4 Time Series . 47 2.5 Vertical Profiles . 52 2.5.1 Traditional Boundary Layer . 52 2.5.2 Upside-Down Boundary Layer . 54 2.6 MultiResolution Flux Decomposition (MRF) . 57 2.7 Personal Case Selection . 62 2.7.1 Wind Threshold . 62 2.7.2 Anisotropy . 64 2.7.3 New Classification of Cases . 66 3 Similarity Theories 67 3.1 Local MOST . 67 3.2 Similarity Functions . 68 3.2.1 Equations . 68 3.2.2 Similarity Functions for Wind . 70 3.2.3 Similarity Functions for Temperature . 73 3.2.4 Eliminating the Dependence on z0 ............ 75 3.2.5 Richardson Numbers . 76 4 Conclusions 82 Acknowledgments . 87 List of Figures 1.1 Idealized time evolution of the atmospheric boundary layer [Stull, 1988]. ............................ 15 1.2 Time series of the three components of the wind speed in the surface layer, from Trombetti and Tagliazucca [1994]. ..... 21 1.3 Illustration of how to anticipate the sign of turbulent heat flux for small-eddy (local) vertical mixing across a region with a lin- ear gradient in the mean potential temperature (from Wallace and Hobbs [2006]). ........................ 25 2.1 Location of the CIBA site within a schematic description of the topographical features of the north-western Iberian peninsula. The light shaded areas are mountain ranges, while the dark shaded area is the Torozos plateau (Cuxart et al. [2000]). The short dashed lines over the plateau area are the cross sections for Fig.2.2. ............................ 42 2.2 Upper diagram: north-west to south-east schematic cross sec- tion of the Torozos Plateau; lower diagram: north-east to south- west schematic cross section (Cuxart et al. [2000]). ...... 43 2.3 Histogram of the frequencies of the wind's directions through- out the entire period. The green bars indicate the directions considered in the z0m analysis. .................. 45 2.4 Values of z0m in near-neutral conditions. The horizontal line represents the calculated average value of z0m = 0:049m. .... 46 2.5 Time series of the potential temperature over the period 16-17 September 1998. .......................... 48 5 6 LIST OF FIGURES 2.6 Time series of the wind speed over the period 16-17 September 1998. ................................ 49 2.7 Time series of the gradient Richardson number Rg over the period 16-17 September 1998. .................. 50 2.8 Time series of the turbulent kinetic energy TKE at three dif- ferent heights (5:8m, 13:5m and 32m) over the period 16-17 September 1998. .......................... 50 2.9 Time series of the turbulent kinetic energy TKE at 5:8m over the period 16-17 September 1998. Plotted on the graph there are indicators for the different cases which can define the state of the SBL. Where no points are shown, the fluxes couldn't be calculated or the heat and momentum fluxes didn't have the same behaviour. .......................... 51 2.10 Like Fig. 2.8 but only the time period 03:00-05:50 Local Time. 51 2.11 Time series of the TKE at 00:00-02:00 LT, 16-Sep during an upside-down SBL. ......................... 52 2.12 (a) Left panel: profile of the TKE at 03:00 LT, 17-Sep. (b) 2 Right panel: profile of the momentum flux (u∗) and the thermal flux (jθ∗u∗j) at 17-Sep, 03:00 LT. ................ 53 2.13 Potential temperature profiles at two different times (03:00 and 05:00 LT). ............................. 55 2.14 Derivative of the potential temperature profiles represented in Fig. 2.13. The vertical lines indicate the threshold under which the slope is considered zero, while the horizontal lines are the estimate of the temperature height ht of the SBL. ... 55 2.15 Cumulative wind speed profile showing all the different values of the wind speed over the time period 03:00-05:00 LT, 17-Sep. 56 2.16 (a) Left panel: profile of the TKE at 01:00 LT, 16-Sep. (b) 2 Right panel: profile of the momentum flux (u∗) and the thermal flux (jθ∗u∗j) at 01:00 LT, 16-Sep. ................ 56 2.17 Cumulative wind speed profile showing all the different values of the wind speed over the time period 00:00-02:00 LT, 16-Sep. 58 LIST OF FIGURES 7 2.18 Wind profiles showing the development of a low level jet during the second night of observations at different times. ....... 58 2.19 Potential temperature profiles at two different times (00:00 and 02:00 Local Time). ........................ 59 % 2.20 Time series of ∆r during the second (left panel) and third (right panel) nights of the experiment. .............. 60 % 2.21 The variation of ∆r with stability using Rg. .......... 61 % MRF 2.22 The variation of ∆r with u∗ . ................. 61 2.23 Scatter plot of ζ(5.8m), calculated with EC and MRF methods. 63 2.24 Normalized δ(v) and correspondent fits functions at 5:8m, 13:5m and 32m. ............................. 63 2.25 Scatter plot of wind speed at 5.8m versus Rg. .......... 65 2.26 Variation of anisotropy with (a) the stability parameter ζ, (b) gradient Richardson number Rg and (c) bulk Richardson num- ber Rb. ............................... 65 2.27 Variation of anisotropy with the bulk Richardson number, fit function and Threshold value for Rb. .............. 66 −1 3.1 Υm(ζ; ζ0m) versus ΛMO for all the data in the dataset at: (a) 5.8m, (b) 13.5m and (c) 32m. Similarity functions found by different authors are also shown for comparison. ........ 71 3.2 Like Fig. 3.1, separating Case=1,4. ............... 72 3.3 Like Fig. 3.1, separating cases where u > ut(z);Rg < 0:163 and cases where u < ut(z);Rg > 0:163. The different values of ut(z) were defined in Chapter 2.7. .............. 72 −1 3.4 Υh(ζ; ζ0h) versus ΛMO for all the data in the dataset at: (a) 5.8m, (b) 13.5m and (c) 32m. Similarity functions found by different authors are also shown for comparison. ........ 74 3.5 Like Fig. 3.4, separating Case=1,4. ............... 74 3.6 Like Fig. 3.4, separating cases where u > ut(z);Rg < 0:163 and cases where u < ut(z);Rg > 0:163. The different values of ut(z) were defined in Chapter 2.7. .............. 75 8 LIST OF FIGURES −1 3.7 Υm(ζ1; ζ2) versus ΛMO for all the data in the dataset. Wind speeds are calculated at z1 = 13:5m and z2 = 5:8m, and u∗ is evaluated averaging u∗(5:8) and u∗(13:5). Similarity functions found by different authors are also shown for comparison. ... 77 −1 3.8 Υh(ζ1; ζ2) versus ΛMO for all the data in the dataset. Potential temperatures are calculated at z1 = 10:88m and z2 = 0:88m, and θ∗ is evaluated at 5:8m. Similarity functions found by different authors are also shown for comparison. ........ 77 −1 3.9 Richardson numbers versus stability parameter ΛMO at z=5.8m. (a) Rf , (b) Rg and (c) Rb. .................... 79 3.10 Υm versus Rg(z) for all the data in the dataset. Functions calculated from similarity functions of different authors are shown for comparison. ...................... 80 3.11 Υm versus Rg(z) for all the data in the dataset, divided by the wind speed as we defined in Chapter 2.7. Functions calculated from similarity functions of different authors are shown for comparison. ............................ 80 3.12 Υh versus Rg(z) for all the data in the dataset. Functions calculated from similarity functions of different authors are shown for comparison. ...................... 81 3.13 Υh versus Rg(z) for all the data in the dataset, divided by the wind speed as we defined in Chapter 2.7. Functions calculated from similarity functions of different authors are shown for comparison. ............................ 81 −1 4.1 Υh versus ΛMO for all the data in the dataset, showing the common data points between the different cases formulations. 85 −1 4.2 Υh versus ΛMO for all the data in the dataset, showing the common data points between the different cases formulations. 85 Sommario L'obiettivo di questa dissertazione `equello di studiare la struttura e il comportamento dello Strato Limite Atmosferico, in condizioni stabili. Questo tipo di strato limite non `eancora completemente compreso appieno, anche se `emolto importante per molti utilizzi pratici, che vanno dalla modellizzazione previsionale, alla dispersione di agenti inquinanti in atmosfera.