Characteristics of the night and day time atmospheric boundary layer at Dome C, Antarctica S. Argentini, I. Pietroni,G. Mastrantonio, A. Viola, S. Zilitinchevich ISAC-CNR Via del Fosso del Cavaliere 100, 00133 Roma, Italy Email : s.argentini@isac.cnr.it Outline : 1. The STABLEDC field experiment : objectives of the experiment and instrumentation (first winter over at Concordia 2005-2006), 2. Behaviour of meteorological parameters: wind histogram, radiative budget, temperature, wind and sensible heat flux behaviour, 3. Thermal structure of the PBL in summer and winter and associated meteorological parameters, 4. High resolution temperature profiles, temperature gradients in summer and winter, 5. Warming events: origin, periodicity and impact on wind field, 6. Future work : background and proposed field and modelling activities. STABLEDC (STABLE boundary layer at Dome C) winter over 2005-2006 Scientific objective : Study of the processes occuring in PBL Long- lived stable boundary layer Summer convective boundary layer Behavior of the temperature inversion during the year Warming events during the winter Interaction between local and large scale circulation INSTRUMENTATION AND MEASUREMENTS Surface measurements : turbulence, mean variables Radiative budget, Energy budget Ground based remote sensing: Temperature, Wind, Aerosol profiles
Concordia Station Surface measurements : turbulence, mean meteorological measurements PERMANENT 13-m Tower thermometers hygrometers wind probes 1.25, 2.5, 5, 10,13 m. 3 m- mast Sonic anemo-thermometer mod. USA - 1 (Metek) Fast response lyman-alphahygrometer (only summer ) Surface Layer Profiles - Wind and temperature in the surface layer - Comparison between results obtained with different fluxes parameterisations (gradient method, eddy correlation, etc). Energy Budget: Turbulent Fluxes (Heat, Latent, Momentum)
Radiation and ground flux measurements Conventional HFP01 heat flux plates at depth of 0, 5, 15, 30, 50 cm Radiometer mod.cnr-1 (Kipp and Zonen) with two pyranometers (CM3) up and down two pyrgeometers (CG3 ) up and down Radiative budget: - Incoming and outgoing shortwave and longwave radiation. -Albedo Sub-surface energy fluxes Snow temperature profiles Ground based remote sensing Passive Microwave radiometer (MPT 5) by Kipp&Zonen. Range 0-600 m Triaxial Doppler mini-sodar Range 12-400 m Resolution 13 m PBL Profile -Development and break down of atmospheric inversions over the course of the time -Temperature Resolution : 0-100 m 10 m 100-200 m 15 m 200-300 m 20 m above 200m 50 m PBL Profiles - Thermal structure of the ABL - Boundary layer depth - High resolution horizontal and vertical velocity profile)
Wind Speed Summer Autumn Winter Spring 500 400 SW SW LW LW Radiation (Wm -2 ) 300 200 WINTER 100 SUMMER AUTUMN SPRING SUMMER 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Time (Hour)
T e m p e r a t u r e S e n s ib le h e a t flu x W i n d s p e e d Structure of the PBL in summer and winter
Convection During Summer DOME C HALLEY King J.C., Argentini S., P. Anderson, 2006. Contrasts between the summertime surface energy balance and boundary layer structure at Dome C and Halley stations, Antarctica. J. of Geophysical Research Vol. 3 D02105
SPEED DIRECTION Sensible Heat Flux Turbulent Kinetic Energy Wind shear absent Stable Boundary Layer 600 500 b) 400 Height (m) 300 200 100 0-70 -65-60 -55-50 -45-40 Temperature ( C)
SPEED DIRECTION Sensible Heat Flux Turbulent Kinetic Energy Typical temperature profiles
Temperature profiles Temperature, Potential temperature and temperature gradient 6 July, 2005
Average Temperature and Temperature Gradients profiles Summer Winter Autumn Spring Diurnal Behaviour of Temperature gradient -------- T( H=inflection height ) T( ground ) Temperature gradient in surface layer - WINTER Temperature gradient in surface layer during stability - SUMMER Temperature gradient in surface layer during convection - SUMMER
TEMPERATURE DIFFERENCE [ T(100) T(0) ] IN WINTER AND SUMMER AT 0200 LOCAL TIME Winter Autumn Spring Summer Summer Estimate of PBL height from radiosounding temperature profiles 1 h 2 E = f 2 2 2 2 ( C u ) ( C u ) ( ) 2 R * + N f CN * + C fb NS S u * C R =0.7 C CN =1.36 C NS =0.51 N= Brunt Vaisala Frequency = 1 2 g ϑ T z z> h f = Coriolis parameter u * = friction velocity B S = buoyancy flux at the surface Zilitinchevic, S., Esau, I., Baklanov., A., 2006: Further comments on the equilibrium height of neutral and stable planetary boundary layer, Quart. J. Roy. Meteorol. Soc., In press Zilitinchevic, S., Esau, I, 2006: Similarity theory and calculation of turbulent fluxes at the surface for the stably stratified atmospheric boundary layers, Boundary-layer Meteorology, In press
Warming events Temperature behaviour during the winter (sonic anemometer data)
Argentini S., I. V. Petenko, G. Mastrantonio, V. A. Bezverkhnii, and A. P. Viola, 2001; Spectral characteristics of East Antarctica Meteorological Parameters during 1994. J. of Geophysical Research, Vol. 106, N D12, p. 12463-12476. Argentini S., I. V. Petenko, G. Mastrantonio, V. A. Bezverkhnii, and A. P. Viola, 2001; Spectral characteristics of East Antarctica Meteorological Parameters during 1994. J. of Geophysical Research, Vol. 106, N D12, p. 12463-12476.
Behaviour of temperature gradient with surface temperature Future work
Background In Antarctica, long-lived stable PBLs are in direct contact with the free atmosphere. Then the standard theory of the nocturnal stable PBL is not applicable. Instead of the PBL as such, we need to consider a two-layer system consisted of the PBL and the capping inversion (CI) developing in the course of time due to the persisting radiative cooling of the ice/snow surface. Here, PBLs - the layers with large turbulent kinetic energy (TKE) - are generally shallow (about 30 m), while CIs, with rather low TKE but strong temperature fluctuations and hence pronounced turbulent potential energy (TPE), could be quite deep. From the mean temperature profiles it is impossible to distinguish between the PBL and the CI. Strong temperature fluctuations (large TPE) responsible for CN2 peaks are observed in PBLs and also in CIs (where they are caused by interaction of weak turbulence basically transported form the PBL with very sharp temperature gradients). Astronomical observations require low CN2 (i.e. low TPE). The PBL height is the key parameter characterizing the lower layer of the atmosphere with strong TPE. To monitor, understand and model the PBL-CI system during winter we propose: Sodar measurements needed to obtain a general picture of the temperature fluctuation field within and above the stable PBL and to estimate the PBL height (however they cannot cover all possible cases). MPT5 Measurements : high resolution temperature profiles to monitor the temperature gradient Real-time numerical large eddy simulation (LES) study of the PBL-CI system covering the entire autumn-winter period over Dome C focused on the vertical / temporal distribution of the TPE (then squared temperature fluctuations, then CN2) and other required parameters. Measurements - complementary to currently performed: Basic turbulence measurements at 1 level (3 m) Mean profiles of wind and temperature in the lower 20 m (7-8 levels) - needed (i) to understand if Katabatic winds occur and (ii) to compute Richardson numbers close to the surface Experimental data and LES would complement each other and allow quantifying mechanisms of generation and maintaining of TKE / TPE over Dome C and giving reliable scenaria of typical winters for use in optimal planning of the construction work and future astronomical observations.
SODAR (Sound Detection and Ranging) Using acoustic waves the sodar gives a picture of the thermal structure of the atmosphere. Setting of the sodar antennas vertically pointing one (up to 3) transmitting and one receiving; height resolution 5 m, first range gate 5 m; maximum reached height 100 m. To be tested and run at Dome C by ISAC. LES (Large Eddy Simulation) Existing turbulence closures do not guarantee representation of very stable stratification, especially temperature fluctuations (that is the TPE): until present, modellers focused on turbulent fluxes and TKE but basically neglected TPE. In capping inversions (CI) generation TPE is essentially non-local: TKE and partially TPE are transported to CI from PBL by turbulent diffusion and internal waves. Currently, the only reliable method to model these mechanisms is LES. Input data (needed to perform LES) geostrophic wind (including baroclinic shear) U(z,t), V(z,t; and temperature in the free atmosphere T(z,t) radiosounding and reanalysis of NWP data surface roughness lengths for momentum and temperature (to be deduced from the below mentioned mean-profile and turbulence measurements) heat balance at the surface: radiation heat fluxes (all components) and heat flux in snow Bibliography Mastrantonio G., V. Malvestuto, S. Argentini, T. Georgiadis, A. Viola, 1999; Evidence of a convective boundary layer developing on the Antarctic plateau during the summer. Meteorol. Atmos. Phys. 71, 127-132. Argentini S., I. V. Petenko, G. Mastrantonio, V. A. Bezverkhnii, and A. P. Viola, 2001; Spectral characteristics of East Antarctica Meteorological Parameters during 1994. J. of Geophysical Research, Vol. 106, N D12, p. 12463-12476. Petenko I. V. and S. Argentini, 2001 ; The Daily Behaviour of Pressure and Its Influence on the Wind Regime in East Antarctica During Winters 1993 and 1994. J. of Appl. Meteor. Vol. 40 N 7, 1255-1264. Georgiadis T., S. Argentini, G. Mastrantonio, A. Viola, G. Dargaud, R. Sozzi, 2002; Boundary Layer convective-like activity at Dome Concordia, Antarctica. "Il Nuovo Cimento" vol. 25 C, N.4 pag. 425-431. Argentini S., A. Viola, A. Sempreviva, I. Petenko, 2005; Summer PBL height at the plateau site of Dome C, Antarctica., Boundary Layer Meteorology. Vol. 115 Number 3, 409-422 King J.C., Argentini S., P. Anderson, 2006. Contrasts between the summertime surface energy balance and boundary layer structure at Dome C and Halley stations, Antarctica. J. of Geophysical Research Vol. 3 D02105.(13 pagine) Zilitinchevic, S., Esau, I., Baklanov., A., 2006: Further comments on the equilibrium height of neutral and stable planetary boundary layer, Quart. J. Roy. Meteorol. Soc., In press Zilitinchevic, S., Esau, I, 2006: Similarity theory and calculation of turbulent fluxes at the surface for the stably stratified atmospheric boundary layers, Boundary-layer Meteorology, In press