Contents. 3. Flying strategies Needs for turbulence measurements Vertical structure Horizontal spatial variability Thin interfaces Clouds

Transcription

1 Contents 1. Planetary Boundary Layer and clouds - Definition - PBL vertical structure - BL Clouds Shallow convection clouds Deep convective clouds Marine Stratocumulus - PBL in complex terrain 2. Probing PBL turbulence - PBL equations - Probing PBL turbulence - Turbulence statistics Approach, turbulence moments Integral scales autocorrelation function Turbulent Kinetic Energy - turbulence spectra Sampling errors - Estimating PBL processes Flux vertical profiles PBL growth Entrainment PBL scaling 3. Flying strategies Needs for turbulence measurements Vertical structure Horizontal spatial variability Thin interfaces Clouds

2 Lecture I 1h

3 Boundary Layer and clouds Marie Lothon Laboratoire d'aérologie, Toulouse Photo by M. Scherrer

4 Diurnal cycle of the surface and low troposphere Definition of the planetary boundary layer (PBL) Courtesy of B. Campistron Courtesy of R. Hogan

5 Surface forcing (a) Daytime over moist surface (b) Nighttime over moist surface (c) Daytime over dry surface (Desert) (d) Dry air over moist surface (Oasis) Wallace and Hobbes, 2006

6 Two important ways to consider the PBL and clouds: (1) Vertical structure / Evolution (2) Spatial variability / Scales

7 Photo by M. Scherrer

8 PBL vertical structure Stull, 1988 Wallace and Hobbes, 2006

9 Courtesy of Colbert et al, 2008

10 Photo by G. Berry

11 Photo by G. Berry

12

13 Rolls See also Lemone, 1973 and Weckwerth et al, 1997

14 Weckwerth et al, 1997

15 Courtesy of Colbert et al, 2008

16 Photo by M. Lothon

17

18

19 Photo by M.

20 Photo by M.

21 Photo by M.

22 Atmospheric moist convection Stevens, 2005

23 Marine Stratocumulus GOES Channel 1 July UTC DYCOMS RF07

24 Photo by G. Vali

25 Main processes in the stratocumulus-topped marine boundary layer (STBL) - SW radiation - Turbulent mixing - Entrainment - Cloud microphysics

26 Conceptual diagram for the stratocumulus-topped PBL Stevens, 2007 Stevens, 2007

27 VERTICAL STRUCTURE OF THE STBL 4 profiles made within a 4-hour period RF07 July 24 θl qt Zi ql

28 Pockets and Open cells in stratocumulus clouds

29 Pockets and Open cells Stevens et al, 2005

30 Pockets and Open cells Van Zanten et al, 2005 Van Zanten, Stevens et al, 2005

31 Structure of the Trade Cumuli Stevens, 2006 Stevens, 2006

32 PBL in complex terrain U Fr = Nh U Fr = N ( Z i h) * Wallace and Hobbes, 2006

33 Lenticular cloud Photo by M.

34 Wallace and Hobbes, 2006

35 Banner cloud Courtesy of Bart Geers

36 Wallace and Hobbes, 2006

37 Lecture II 1h

38 Probing boundary layer turbulence

39 Resolving Navier-Stokes equation with perturbations u = < u > + u'

40 A possible closure: >> Importance of measuring turbulent variables, To check, suggest and improve parameterizations

41 Probing turbulence from the ground Distance/time/frequency equivalence d = Ut 2π ν k= U

42 Probing turbulence from an aircraft Distance/time equivalence d = Ua t 2π ν k= Ua U a : Airplane True Airspeed! Concepts of «Transverse» and «Longitudinal» are different than when measuring from the ground!

43 In situ measurements of the air motion with an aircraft ~100 m/s (approx.) ~1 m/s ~100 m/s ~0.01 ~1 m/s Lenschow, RAF Bulletin #23

44 Definition and measurements of PBL turbulent processes Content: Statistics Integral scales Fluxes Entrainment Turbulent kinetic energy Higher-order moments

45 Example of measured air vertical velocity time series

46 Example of measured air temperature time series

47 Statistical approach

48 Higher-order moments Variance σ 2 w = < w' > 2 µ 3 = < w'3 > µ 4 = < w' > 4 µ3 S= 3 σ µ4 K= 4 σ Skewness Kurtosis

49

50 (m) Integral scale Lw=195 m Lw=195 m

51 Energy density spectrum Vertical velocity energy spectrum Fw ( f ) = FFT ( w(t )) S w ( f ) = Fw ( f ) Fw * ( f ) S w ( f ) = FFT ( Rw (τ )) Rw (τ ) = IFFT ( S w ( f ))

52 Turbulent Kinetic Energy ( 1 e= σ 2 2 u +σ 2 v +σ 2 w ) 4 S w (k ) = α ε 3 2/3 k 5/ 3 Wave number Kolmogorov constant Dissipation rate (units: m2s-3) Stull, 1988 Wallace and Hobbes, 2006 Production terms (buoyancy and shear) transport pressure dissipation

53 Sampling errors F = limt 1 T w' (t ) s' (t )dt 0 Systematic error 1 N w' (i ) s ' (i ) i = 0: N ~10% Associated for example with limited leg or high pass filtering Random error 10 to >50% Instrumental error < 5% Lenschow, 1994 Mann and Lenschow, 1994

54 Kinematic Fluxes

55 Stull, 1988 Wallace and Hobbes, 2006

56 - pdf Potential temperature BL FT Water vapour mixing ratio BL FT Probing the Sahelian boundary layer + pdf Courtesy of G. Canut, 2010

57 Cloud edges

58 Buoyancy flux vertical structure Courtesy of G. Canut, 2010

59 Vertical profiles of the fluxes in the Sahelian boundary layer Canut et al, 2010

60 Boundary layer growth and warming encroachment entrainment Garratt, 1992

61 Entrainment rate Entrainment velocity δ Zero-order model (ZOM) First-Order Model (FOM)

62 Estimating entrainment from aircraft measurements

63 Boundary layer growth and warming

64 Boundary layer scaling

65 Flying strategies defined as a function of (consensus between): Scientific goals and Capability of the aircraft (autonomy, minimum and maximum heights, airspeed, payload/instruments, )

66 NCAR C130 during DYCOMS-II (DYNAMICS AND CHEMISTRY OF MARINE STRATOCUMULUS) Stevens et al., BAMS, 84 (2003)

67 Studying the boundary layer vertical structure

68 DYCOMS-II DYNAMICS AND CHEMISTRY OF MARINE STRATOCUMULUS CT CB SC SF Stevens et al., BAMS, 84 (2003) RL

69 Fine-scale structure at stratocumulus cloud top Lenschow et al, 2000

70 RICO Rain In Cumulus over the Ocean Rauber, Stevens et al, 2007

71 HiCu High Plains Cumulus Damiani and Vali, 2007

72 CuPIDO Cumulus, Photogrammetric, In situ and Doppler Observations Damiani et al, 2008

73 CuPIDO Cumulus, Photogrammetric, In situ and Doppler Observations Damiani et al, 2008

74 95 GHz WYOMING CLOUD RADAR Antennas diameter 25 cm Beam width 0.7 Peak power 1.6 kw Repetition frequency 5 khz / 20 khz Pulse length 250 ns (33 m) Number of profiles per sec 20 27

75 growing cell in-situ gust-probe data Divergence associated with updraft top reflectivity dbz FSSP total conc. (# cm-3) air temperature (ºC) vertical plane horizontal plane Doppler vertical velocity (m/s) Thermal Core surrounded by descending flow 1d-c total conc. (# L-1) liquid water content (g m-3) Aug 26th, 2003

76 thermal top 1st pass Higher Z at the sides of updraft. Coalescence/ Ice nucleation. Lack of sensitivity

77 July 13th HBDD: final stages Jul 13th, 2003

78 Organized large scale horizontal dynamics Jul 12th, 2003

79 References - Textbooks Garratt, J. R. : The Atmospheric Boundary Layer. Cambridge Atmospheric and Space Science Series, 1992, 316 pp. Lenschow, D. H. : Probing the Atmospheric Boundary Layer. American Meteorological Society, Boston, Massachusetts, 1976, 269 pp. Monin, A. S. and A. M. Yaglom: Statistical Fluid Mechanics II. Massachusetts Institute Technology Press, 1975, 874 pp. Stull, R. B. : An Introduction to the Atmospheric Boundary Layer Meteorology. Kluwer Academin Publishers, 1988, 666 p. Wallace, J. M. and P. V. Hobbes: Atmospheric Science: An introductory Survey. 2d ed. Elsevier, 2006, Wyngaard, J. C. : Turbulence in the Atmosphere. Cambridge University Press, 2010, 393 pp.

80 References - Articles Canut, G., M. Lothon and F. Saïd, 2010: Observation of entrainment at the interface between monsoon flow and Saharan Air Layer, Quart. J. Roy. Meteorol. Soc., 136, Damiani R. and G. Vali, 2007: Evidence for tilted toroidal circulations in cumulus. J. Atmos. Sci., 64, Damiani, R., et al, 2008: The cumulus, photogrammetric, in situ, and Doppler observations experiment of 2006: Bull. Am. Met. Soc., 89, 57-+ Lemone, M. A., 1973: The structure and dynamics of horizontal vortices in the planetary boundary layer. J. Atmos. Sci., 30, Lenschow, D. H, J. Mann and L. Kristensen, 1994: How long is long enough when measuring fluxes and other turbulence statistics? J. Atmos. Oceanic Technol., 11, Lenschow, D. H. et al 2000: Measurements of the fine-scale structure at the top of Marine Stratocumulus. Boundary-Layer Meteorol., 97, Mann J. and D. H. and Lenschow, 1994: Errors in airborne flux measurements. J. Geophys. Res., 99,

81 References - Articles Stevens, B., 2005: Atmospheric Moist Convection. Annu. Earth Planet. Sci. 32, Stevens, B., 2006: Bulk boundary layer concepts for simplifed models of tropical dynamics, heoretical and Computational Fluid Dyn., 20, Stevens, B. et al, 2007: On the structure of the lower troposphere in the summertime stratocumulus regime of the northeast Pacific, Mon. Weath. Rev, 135, Stevens B. et al 2003, Dynamics and Chemistry of Marine Stratocumulus - DYCOMS-II, Bull. Amer. Meteor. Soc., 84, Van Zanten, M. C. and B. Stevens, 2005: Observations of the structure of heavily precipitating marine stratocumuls, J. Atmos. Sci., 62, Weckwerth, T. M., 1997: Horizontal convective rolls: Determining the environmental conditions supporting their existence and characteristics. Mon. Wea. Rev., 125, Rauber, R. M., B. Stevens et al, 2007: Rain in (shallow) cumulus over the ocean The RICO campaign, Bull. of the American Meteorol. Soc., 88,