The Arctic Turbulence Experiment 2006, Direct measurements of turbulent fluxes in the near surface environment at high latitudes applying the eddy-covariance method, Part 2

UNIVERSITY of BAYREUTH Department of Micrometeorology The Arctic Turbulence Experiment 2006 Direct measurements of turbulent fluxes in the near surface environment at high latitudes applying the eddy-covariance method PART 2 Near surface measurements during the ARCTEX 2006 campaign May, 2nd to May, 20th 2006 Johannes Lüers and Jörg Bareiss Work Report No. 32 Bayreuth, August 2007 2 Contents 1 Introduction.......................................................................................................... 3 2 General Information............................................................................................. 4 2.1 Location........................................................................................................ 4 2.2 Surface and weather conditions................................................................... 5 3 Overview of measurement sites.......................................................................... 6 4 Visualization of standard meteorological measurements.................................... 7 4.1 Synoptic situation......................................................................................... 7 4.2 Entire observation period ........................................................................... 20 4.3 Daily charts ................................................................................................ 27 5 Visualization of directly measured turbulence fluxes......................................... 59 5.1 Calculation of turbulent fluxes with the software package TK2.................. 59 5.2 Entire observation period ........................................................................... 60 5.3 Daily charts ................................................................................................ 69 6 Data archived at Ny-Ålesund (CDs) .................................................................. 74 3 1 Introduction Abstract Accurate quantification of turbulent fluxes between the surface and the atmospheric boundary layer in polar environments, characterized by frequent stable to very stable stratified conditions, is a fundamental problem in soil-snow-ice-vegetation-atmosphere interaction studies. The observed rapid climate warming in the Arctic requires improvements in the monitoring of energy and matter exchange; accomplished by setting up appropriate (adapted to polar conditions) observation sites to measure turbulent fluxes. To address these problems, it is essential to improve the databases with high-quality in-situ measurements of turbulent fluxes near the surface applying the EddyCovariance method. These direct measurement data (CSAT3 sonic anemometer, KH20 krypton hygrometer, and laser scintillometer) obtained during the first Arctic Turbulence Experiment (ARCTEX-2006) in May 2006 at the French-German Arctic Research Base in Ny-Ålesund (AWI/IPEV) on Spitsbergen (Svalbard) allowed a comparison with simulated results from simple flux gradientparameterizations used today to force atmosphere-ocean-ice models. In addition, the results of this pilot study shows the problem of direct measurements (e.g. snow drift through the sensor path ways) under rough weather conditions as well as they reveal that the misestimating of sensible heat fluxes can result from inaccurate measurements or calculation of the surface temperature and inappropriate treatment of the neutral and stable conditions (e.g. intermittency, gravity waves) in the bulk parameterization. The primary goals of the ARCTEX-campaign were: 1. continuous measurements of high-resolution (20 Hz) turbulent heat fluxes near the tundra surface using a ultra sonic anemometer (eddy-covariance method) and an ultraviolet krypton hygrometer, 2. continuous measurements of the turbulent sensible heat flux near the tundra surface using the Laser-scintillometry, 3. measurements of standard meteorological data sampled at 1s intervals using a meteorological gradient tower (6 m and 10 m), 4. preand postprocessing of high-quality data sets of turbulent fluxes using state of the art flux data quality assessment techniques, 5. understanding of exchange processes and their parameterization for neutral and stable conditions, 6. validation of commonly used sensible and latent heat flux parameterizations (aerodynamic approach, bulk and gradient method). 4 2 General Information 2.1 Location Detailed geographic locations of the “Arctic Turbulence Experiment 2006” (ARCTEX-2006) at NyÅlesund (Svalbard, Kongsfjorden), May 2006, Universities of Bayreuth and Trier, Germany: General location Svalbard, Kongsfjorden, NyÅlesund, Position (Center of settlement): 078° 55’ 24’’ N, 011° 55’ 15’’ E Eddy-Flux complex UBT (EF): Coordinates: 078° 55’ 02’’ N, 011° 55’ 52’’ E Altitude: 13 m a. s. l. Land use: snow covered tundra Meteorological tower AWI (MT1): Coordinates: 078° 55’ 04’’ N, 011° 55’ 26’’ E Altitude: 14 m a. s. l. Land use: snow covered tundra Meteorological tower UBT (MT2): Coordinates: 078° 55’ 03’’ N, 011° 55’ 34’’ E Altitude: 14 m a. s. l. Land use: snow covered tundra Scintillometer UBT (SLS): Coordinates: 078° 55’ 00’’ N, 011° 56’ 00’’ E Altitude: 13.5 m a. s. l. Land use: snow covered tundra Tethered balloon AWI (TB1): Coordinates: 078° 55’ 06’’ N, 011° 55’ 23’’ E Altitude: 11 m a. s. l. Land use: snow covered tundra Tethered balloon AWI (TB2): Coordinates: 078° 55’ 27’’ N, 011° 56’ 07’’ E Altitude: 3 m a. s. l. Land use: Harbor (concrete), fjord (water) Radiosonde AWI (RS): Coordinates: 078° 55’ 06’’ N, 011° 55’ 23’’ E Altitude: 11 m a. s. l. Land use: snow covered tundra BSRN AWI (BSRN): Coordinates: 078° 56’ 05’’ N, 011° 56’ E Altitude: 11 m a. s. l. Land use: snow covered tundra Time zone Central European Time: CET = GMT + 1 h (winter) CEST = GMT + 2 h (summer). Given times and filenames reflect starting time of intervals UBT=Univ. of Bayreuth; AWI= Alfred Wegener Institute for Polarand Marine Research; BSRN= Baseline Surface Radiation Network 5 2.2 Surface and weather conditions Table 2.1 lists the surface and weather conditions during the ARCTEX-2006 campaign. Noteworthy, is the extreme warm period until evening May 7 and the heavy snow-storm at night, May 7 to May 8. Table 2.1: Surface and weather conditions during the ARCTEX-2006 campaign. May 3 to May 5 wet melting snow over ice, larger snow free spots (bare soil, tundra), surface melt water, some rain fall and partly cloudy, Arctic Haze event, extremely warm, temperature range: +3 °C to +8 °C May 6 to May 8 1st storm and heavy snowfall, heavy snowdrift; overcast weather, extremely warm (+8 °C) until beginning of the 2nd storm on May 7, 19 h CET and temperature drop of more than 16 K (−10 °C) May 9 to May 11 fresh snow cover, predominantly sunny weather, temperature range: − 5 °C to −2 °C May 12 to May 14 ongoing snowdrift, snow cover depleting, at 13th pm temperature around 0 °C, predominantly overcast or partly cloudy weather, temperature range: −4 °C to 0 °C May 15 to May 16 ongoing snowdrift, some snow free spots, at ground refrozen and compacted thin ice layers, predominantly sunny or partly cloudy weather, temperature range: −4 °C to −1 °C May 17 to May 19 melting snow over ice, some snow free spots (bare soil, tundra), light to moderate rain and/or snowfall (17th and 18th, temperature range: −2 °C to +1 °C) 6 3 Overview of measurement sites The map (Figure 3.1) of Ny-Ålesund (Svalbard) shows the measurement sites during the ARCTEX-2006 campaign. The permanent AWI/IPEV sites used for this study are the 10 m meteorological tower of the Alfred Wegener Institute for Polar and Marine Research (MT1), the international standardized radiation measurements of the Baseline Surface Radiation Network (BSRN), the WMO 1004 radiosonde launch site (RS) and the temporary AWI tethered balloon launch sites TB1 and TB2. The temporary sites - build up by the Universities of Bayreuth and Trier - are the 6 m meteorological tower (MT2), the eddy-flux measurement complex with sonic anemometer (EF), and the Laser-scintillometer pathway (SLS). TB2 RS TB1 MT1 MT2 EF SLS BSRN Eddy-Flux Complex UBT Meteorological Gradient Tower UBT Scintillometer UBT Figure 3.1: Map of Ny-Ålesund (Svalbard, Kongsfjorden) showing the measurement sites during the ARCTEX-2006 campaign: MT1 (10 m meteorological tower of the Alfred Wegener Institute for Polar and Marine Research), MT2 (6 m meteorological tower of the University of Bayreuth), EF (eddy-flux measurement complex), SLS (site for scintillometer measurements), BSRN (radiation measurements of the Baseline Surface Radiation Measurements), RS (radiosonde launch site), TB1 and TB2 (tethered balloon launch sites). The base map was kindly provided by the Norwegian Polar Institute. 7 4 Visualization of standard meteorological measurements 4.1 Synoptic situation Operational Surface Analysis Charts of the Meteorological Service of Canada, Weatheroffice (www.weatheroffice.gc.ca), complete Northern Hemispheric coverage. The following charts of the Global Environmental Multiscale Model (GEM) outline the synoptic situation between May 5 and May 18, 2006. Remarkable was the passage of an arctic cyclone on May 7 and May 8, 2006 across Spitsbergen causing heavy snow fall and wind speeds up to more than 80 km/h. 8 9 16 17 18 19 20 4.2 Entire observation period Temperature During the ARCTEX-2006 campaign the temperature drops from +8 °C to −9 °C during the passage of a cold front of an arctic storm cyclone in the night of May 7 to May 8, 2006 (Figure 4.1). Afterwards, until the morning of May 12, a period of sunny, clear sky weather occurs resulting in a strong positive temperature gradient (temperature inversion) and extreme stabile stratification in between the first 10 m above the snow cover in the three “nights” May 9 to May 12 (compare Figure 4.1 and Figure 4.2.). Only around noon of May 13, May 14 and May 16 a light negative temperature gradient accompanied by a breakdown of the wind system occurs each time just for few hours resulting in a weak positive heat flux. Figure 4.1: Air temperature May 5 to May 19, 2006. Black dots: air temperature in °C at 0.7 m a. g. l. (gradient tower MT2, Univ. of Bayreuth). Grey dots: air temperature in °C at 10.0 m a. g. l. (meteor. tower MT1, Alfred Wegener Institute for Polar and Marine Research). Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. Figure 4.2: Vertical difference of air temperature and wind speed May 5 to May 19, 2006. Black dots: ∆T difference of air temperature in K between 10 m and 0.7 m a. g. l. Grey dots: ∆u difference of wind speed in m s−1 between 10.0 m and 0.7 m a. g. l. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 21 Humidity The low level of the absolute humidity amount around 2 to 3 g m−3 is typical for a cold arctic air mass. Only under influence of the warm air mass sector of the passing cyclone the water vapor amount increases significant but reaching saturation only during the heavy snow storm at May 7 (Figure 4.3). Figure 4.3: Humidity May 5 to May 19, 2006. Black dots: relative humidity in % at 1.5 m a. g. l. Grey dots: absolute humidity in g m−3 at 10.0 m a. g. l. (both meteor. tower MT1, Alfred Wegener Institute for Polar and Marine Research). Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. Wind speed and wind direction The horizontal wind speed at different heights above ground level (0.7 m up to 10 m) was obtained by the gradient tower of the University of Bayreuth (MT2) using the Climatronics F460 cup anemometers as well by the routine observation of the meteorological tower of the Alfred Wegener Institute for Polar and Marine Research (MT1). Figure 4.4: Wind speed May 5 to May 19, 2006. Black dots: wind speed in m s−1 at 0.7 m a. g. l. (gradient tower MT2, Univ. of Bayreuth). Grey dots: wind speed in m s−1 at 10.0 m a. g. l. (meteor. tower MT1, Alfred Wegener Institute for Polar and Marine Research). Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 22 The Figure 4.4 indicates that at most of the time the usual vertical wind profile dominates. During few periods between May 7 and May 12 (esp. during the clear sky days) the near surface wind speed (first 3 m) exceeds the speeds at 10 m a. g. l. (compare Figure 4.2). A closer look reveals a more or less 2 m to 3 m thick air flow coming from south-west downhill the slope from the near Zeppelin Mountain Range. Figure 4.5: Wind direction and wind speed May 5 to May 19, 2006. Black dots: wind speed in m s−1 at 10.0 m a. g. l. Grey dots: wind direction in degree at 10.0 m a. g. l. (both meteor. tower MT1, Alfred Wegener Institute for Polar and Marine Research). The small bars at the plot’s top boarder indicate significant change of the wind regime (namely SE and NW) or a transition phase. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. The Figure 4.5 compares wind speed and the corresponding direction. Between May 8 and May 12 the prevailing wind direction is north-west (upwards the fjord) interrupted at midday May 9 by indifferent directions and relatively calm wind conditions and during May 11 by change to a strong south-east air flow. Beginning around midnight May 12 until noon May 16 the prevailing direction remains south-east (downward the Kongsfjord). At afternoon May 16 a relatively warm and humid air mass arrived in Ny-Ålesund due to a low pressure system across the Barents Sea. The wind direction (at 2 m and 10 m a. g. l.) was obtained by the meteorological routine observation of the 10 m tall meteorological tower of the Alfred Wegener Institute for Polar and Marine Research (MT1). The used wind sensor is a combined anemometer and wind vane (Thies Clima, Germamy). The Figure 4.6 illustrates the both main wind direction sectors at NyÅlesund during the ARCTEX-2006 campaign. This pattern of either south-east or north-west directions (more or less canalized air flow down or upward the Kongsfjord) is typical not only in May but also most of the time during the year. At 2 m and during weak wind an offshore south-west component is distinguishable (compare Chapter 4.3: daily wind rose plots). 23 Figure 4.6: Frequency distribution of wind direction separated in 12 wind sectors and classified in 4 wind speed classes, May 1 to May 18, 2006. Above: distribution of the wind directions in degree measured at 2.0 m height a. g. l. Below: distribution of the wind direction in degree measured at 10.0 m a. g. l. (both meteor. tower MT1, Alfred Wegener Institute for Polar and Marine Research). Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 24 Radiation The radiation measurements took place at the routine BSRN-Station (AWI) and at the ARCTEX2006 measurement field next to the gradient tower of the Univ. of Bayreuth (MT2). At the latter site the radiation measurement equipment was especially build-up over an adequate thick snow field. At the BSRN site a pattern of more or less snow covered or snow free tundra around the instrument field yields to a slightly reduced amount of reflected shortwave radiation in comparison to the MT2 site whereas the global radiation received at both sites are remarkable similar (compare Figure 4.7 and Figure 4.8). Figure 4.7: Global shortwave radiation May 5 to May 19, 2006. Black dots: global radiation in W m−2 measured with a CM11 (Kipp & Zonen) pyranometer (BSRN station, Alfred Wegener Institute for Polar and Marine Research). Grey dots: global radiation in W m−2 measured with a CNR1 (Kipp & Zonen) net radiometer (net radiation station Univ. of Bayreuth). Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. Figure 4.8: Reflected shortwave radiation May 5 to May 19, 2006. Black dots: reflected radiation in W m−2 measured with a CM11 (Kipp & Zonen) pyranometer (BSRN station, Alfred Wegener Institute for Polar and Marine Research). Grey dots: reflected radiation in W m−2 measured with a CNR1 (Kipp & Zonen) net radiometer (net radiation station Univ. of Bayreuth). Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 25 Figure 4.9: Ratio of reflected (only values above or equal 10 W m−2) to global shortwave radiation (albedo) measured with a CNR1 (Kipp & Zonen) net radiometer (net radiation station Univ. of Bayreuth) May 5 to May 19, 2006. Circles show the daily variance of the Albedo due to different elevation angles of the sun and due to different fraction of the half space from witch diffuse sky radiation or the - from the surface - reflected radiation can reach the sensors. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. The interpretation of the albedo in polar regions especially during snow fall or snow melt seasons is difficult. The Figure 4.9 demonstrates this problem. During snow fall events like between May 6 and May 7, the albedo changed rapidly covering a more or less snow free surface with fresh snow. At times with clear sky weather and lower rate of diffuse radiation and a new fresh and closed snow cover like from May 8 to May 10 the albedo varies in a large range depending on the elevation angle and the superimposed effect of additional reflected radiation receiving the sensor caused by the reflection of the surrounding snow covered earth surface according to the local limitation or extension of the horizon. Otherwise, at days with decreasing snow cover and a higher rate of diffuse radiation like May 12 to May 14 or May 17 the daily variation of the albedo is relatively small. Figure 4.10: Longwave radiation measured with a PIR (Precision Infrared Radiometer, Eppley) Pyrgeometer (BSRN station, Alfred Wegener Institute for Polar and Marine Research) May 5 to May 19, 2006. Black dots: incoming long wave radiation in W m−2.Grey dots: outgoing long wave radiation in W m−2. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 32 Wind speed The wind speed was recorded in different heights above ground using cup anemometers. Most of the time the area around the gradient tower of the University of Bayreuth (MT2, measuring heights 0.7 m, 1.4m, 2.4 m and 3.9 m) and around the meteorological tower of the Alfred Wegener Institute for Polar and Marine Research (MT1, 10 m) was covered by 20 cm to 30 cm snow. The records of the cup anemometer mounted at 5.6 m had to be neglected because of a damage of the ball bearing after the storm event May 7, May 8. 33 34 35 36 37 Wind direction The wind direction was recorded with a wind vane at the meteorological tower of the Alfred Wegener Institute for Polar and Marine Research Ny-Ålesund (MT1) in 2 m and 10 m above the ground nearby the gradient tower and the eddy flux complex of the University of Bayreuth. The general calm limit was set to < 0.3 m s−1. At most of the days between May 1 and May 18 the percentage of clam events are below 1 % of all measurements per day. The wind rose plots are a combination of wind speed and related direction to succinctly show the daily distribution or frequency of particular directions separated in 12 sectors. The chosen wind speed class limits are >= 0.3 to 1.6, > 1.6 to 3.4, > 3.4 to 8.0 and > 8.0 m s−1. Noticeable are the offshore south-west components during weak wind especially at May 9 and May 11. 38 39 40 41 48 49 Longwave radiation The presented recordings of the terrestrial radiation and the cloud base height are obtained by the international standardized radiation measurements of the Baseline Surface Radiation Network (BSRN) and the laser ceilometer (cloud base height) both maintained by the Alfred Wegener Institute for Polar and Marine Research. The plots show the incoming and outgoing fluxes in the longwave spectral range and the according cloud height. 50 51 52 53 54 Cloud Base height in meter 55 56 57 64 Ny-Alesund 0 1 2 3 4 5 6 7 8 9 10 Time [Day] u∗ steady state quality flag 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 07 08 09 10 11 12 13 14 15 16 17 18 19 20 May 2006 u∗ [m s−1] statflag_ustar friction velocity Figure 5.9: Friction velocity u∗ (at 2.4 m above ground) obtained by the eddy covariance complex EF and the related quality flags of the Steady State test (Foken & Wichura, 1996; TK2-software) of the covariance of the fluctuations of the horizontal (u', v') and vertical (w') wind components (statflag_ustar). The classes 1 to 3 are good quality, the classes 4 to 6 are usable quality, class 7 and 8 are only for orientation, 9 has to be neglected, May 7 to May 19, 2006. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. Ny-Alesund 0 1 2 3 4 5 6 7 8 9 10 07 08 09 10 11 12 13 14 15 16 17 18 19 20 Time [Day] QHB steady state quality flag -40 -30 -20 -10 0 10 20 30 40 May 2006 QHB [W m−2] buoyancy flux statflag_wTs Figure 5.10: Buoyancy flux QHB (due to the very low water vapor contend during May 2006 equatable to the real sensible heat flux QH) at 2.4 m above ground obtained by the eddy covariance complex EF and the related quality flags of the Steady State test (Foken & Wichura, 1996; TK2-software) of the covariance of the fluctuations of the sonic temperature (Ts') and vertical (w') wind component (statflag_wTs). The classes 1 to 3 are good quality, the classes 4 to 6 are usable quality, class 7 and 8 are only for orientation, 9 has to be neglected, May 7 to May 19, 2006. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 65 Ny-Alesund 0 1 2 3 4 5 6 7 8 9 10 07 08 09 10 11 12 13 14 15 16 17 18 19 20 Time [Day] itc (σT / T∗) quality flag -40 -30 -20 -10 0 10 20 30 40 May 2006 QHB [W m−2] buoyancy flux itcflag_Ts Figure 5.11: Buoyancy flux QHB (due to the very low water vapor contend during May 2006 equatable to the real sensible heat flux QH) at 2.4 m above ground obtained by the eddy covariance complex EF and the related quality flags of the Integral Turbulence Characteristic test (ITC-test, Foken & Wichura, 1996; TK2software) of the standard deviation (σTs) normalized by its dynamical parameter T∗ (itcflag_Ts). The classes 1 to 3 are good quality, the classes 4 to 6 are usable quality, class 7 and 8 are only for orientation, 9 has to be neglected, May 7 to May 19, 2006. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. Ny-Alesund May 2006 0 10 20 30 40 50 60 70 80 123456789 class % statflag_wTs statflag_ustar Ny-Alesund May 2006 0 10 20 30 40 50 60 70 80 123456789 class % itcflag_Ts itcflag_w Figure 5.12: Quality control using the quality flag system after Foken & Wichura (1996) by applying the TK2-software. Left: Steady State test of the covariance of the fluctuations of a) the horizontal wind components (u', v') and b) the sonic temperature (Ts') and the vertical (w') wind component (statflag_ustar and statflag_wTs). Right: Integral Turbulence Characteristic test (ITC-test) of the standard deviations (σw and σTs) normalized by their dynamical parameters u∗ and T∗ (itcflag_w and itcflag_Ts). The classes 1 to 3 are good quality, the classes 4 to 6 are usable quality, class 7 and 8 are only for orientation, 9 has to be neglected, May 7 to May 19, 2006. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 66 Ny-Alesund -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0 45 90 135 180 225 270 315 360 φ [°] w [m s−1] unrotated May 2006 Ny-Alesund -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0 45 90 135 180 225 270 315 360 φ [°] w [m s−1] rotated May 2006 Ny-Alesund -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0 2 4 6 8 10 12 vh [m s−1] w [m s−1] unrotated May 2006 Ny-Alesund -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0 2 4 6 8 10 12 vh [m s−1] w [m s−1] rotated May 2006 Figure 5.13: Quality control of the turbulent fluxes obtained by the eddy covariance complex EF applying the Planar Fit coordinate rotation method after Wilczak et al. (2001) ideally resulting in a w-value of zero averaged over the whole data set May 7 to May 18, 2006. The plots show the correction effect (left with unrotated, right with rotated coordinate matrix) regarding the vertical wind component w in relation to the according wind direction φ (above) and regarding the vertical wind component w in relation to the according horizontal wind speed vh (below). Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 67 Ny-Alesund -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Time [Day] z/L ζ [ ] -40 -30 -20 -10 0 10 20 30 40 07 08 09 10 11 12 13 14 15 16 17 18 19 20 May 2006 QHB [W m−2] stability z/L buoyancy flux Figure 5.14: Buoyancy flux QHB (due to the very low water vapor contend during May 2006 equatable to the real sensible heat flux QH) at 2.4 m above ground (black dots) and the related atmospheric stability parameter ζ (z/L), whereas L is the Obukhov-length and z is the measurement height (2.4 m), both obtained by the eddy covariance complex EF. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. Ny-Alseund -40 -30 -20 -10 0 10 20 10 11 12 13 14 15 16 17 18 19 Time [Day] QHB [W m−2] -40 -30 -20 -10 0 10 20 May 2006 Ecv SLS Qh 5.6m-0.7m SLS Qh Ri Figure 5.15: Comparison of the sensible heat flux obtained by tow independent measurement systems during May 7 and May 19, 2006, nearby Ny-Ålesund (Svalbard). The grey line (Ecv) indicates the sensible heat flux QH at 2.4 m above ground obtained by the eddy covariance complex EF using a Campbell CAST3. The solid and dotted black lines indicates the sensible heat flux along a 104 m long laser scintillometer pathway (Scintec SLS-20) 1.5 m above ground covering the same fetch as the sonicanemometer. For the solid line (SLS QH Ri) the bulk Richardson number was used and for the dotted line (SLS QH 5.6m−0.7m) the vertical gradient of air temperature between 5.6 m and 0.7 m was used to decide the appropriate flux directions. To calculate the Ri-Number and the temperature gradient the data of both gradient towers MT1 and MT2 were used. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 68 Ny-Alesund 0 45 90 135 180 225 270 315 360 07 08 09 10 11 12 13 14 15 16 17 18 19 20 Time [Day] Wind direction φ [°] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 May 2006 u∗ [m s−1] 07 08 09 10 11 12 13 14 15 16 17 18 19 20 Stability z/L ζ [ ] -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Figure 5.16: Recorded wind direction φ (crosses) and the friction velocity u∗ (grey line), and the related atmospheric stability parameter ζ (z/L, black dots, pos. values = stable, neg. values = unstable), whereas L is the Obukhov-length and z is the measurement height (2.4 m), all obtained by the eddy covariance complex EF, May 7 to May 19, 2006. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. Ny-Alesund 0 45 90 135 180 225 270 315 360 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 CET [Hour] Wind direction φ [°] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 May 16, 2006 u∗ [m s−1] 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 Stability z/L ζ [ ] -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Figure 5.17: Recorded wind direction φ (crosses) and the friction velocity u∗ (grey line), and the related atmospheric stability parameter ζ (z/L, black dots, pos. values = stable, neg. values = unstable), whereas L is the Obukhov-length and z is the measurement height (2.4 m), all obtained by the eddy covariance complex EF, selected day May 16, 2006. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. Ny-Alesund 0 45 90 135 180 225 270 315 360 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 CET [Hour] Wind direction φ [°] 0.0 0.1 0.2 0.3 0.4 May 13, 2006 u∗ [m s−1] 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 Stability z/L ζ [ ] -10 -8 -6 -4 -2 0 2 Figure 5.18: Recorded wind direction φ (crosses) and the friction velocity u∗ (grey line), and the related atmospheric stability parameter ζ (z/L, black dots, pos. values = stable, neg. values = unstable), whereas L is the Obukhov-length and z is the measurement height (2.4 m), all obtained by the eddy covariance complex EF, selected day May 13, 2006. Ny-Ålesund (Svalbard), ARCTEX-2006 campaign. 69 5.3 Daily charts The figures in this chapter present the two directly measured sensible heat fluxes including the atmospheric stability parameter ζ (z/L) during the ARCTEX-2006 campaign May 7 to May 18 and the calculated sensible heat flux applying the model approach of Launiainen & Cheng, 1995 (Turbflx). For the latter approach the eddy covariance independent meteorological measurements of both gradient towers MT1 and MT2 as well as the BSRN-station were used. As input for the Turbflx-model the required ground (snow) surface temperature was recalculated from the outgoing longwave radiation values of the nearby BSRN-station. To determine the drag coefficient or bulk transfer coefficient a snow/ice covered land surface was assumed (QH Tfx Rad snow). The two direct approaches utilized a) the CSAT3 eddy covariance complex EF (QHB Ecv) and b) the laser-scintillometer section (QH SLS Ri). For the analysis of the scintillometer measurements the bulk Richardson number was used to decide the appropriate flux directions instead the usual vertical gradient of air temperature. Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 7, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 8, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv 70 Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 9, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 10, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 11, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv 71 Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 12, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 13, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 14, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv 72 Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 15, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 16, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 17, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv 73 Ny-Alesund -3 -2 -1 0 1 2 3 CET [hour] z/L ζ [ ] -30 -20 -10 0 10 20 30 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 00 May 18, 2006 QH [W m−2] Stability z/L Qh Tfx Rad snow Qh SLS Ri Qhb Ecv