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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Boundary layer meteorology 61 (1992), S. 213-245 
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Conditional sampling is used to locate coherent structures in a large data set obtained from flights by an instrumented light aircraft in convective boundary layers over Eyre Peninsula, South Australia. The high resolution and excellent spatial coverage of the data enable a detailed study of the internal structure of surface-layer plumes and mixed-layer thermals. A compositing technique is used to construct averaged traverses through coherent structures located within aircraft data runs of different altitudes and directions. Groups of composites are combined to form horizontal and vertical cross-sections which describe the internal flow patterns and the distribution of physical variables associated with “typical” coherent structures and their environment. In addition to the well-known along-wind features of surface-layer plumes, a strong, consistent inflow/entrainment pattern is evident in the lateral direction. Air from the horizontal plane channels around the sides and then in behind the microfront present at the upstream edge. Forces set up by the driving instability in the along-wind and vertical directions are counter-balanced by organised flow in the across-wind direction. It is found that mixed-layer thermal towers have a relatively simple form, consisting primarily of large columns of warm, upward-moving turbulent air, which may occasionally be in a state of slow rotation. An analysis of possible geometrical distortions within the results is performed, leading to a comparison ofδw/δz estimated from the horizontal velocity convergence field inside plumes/thermals, with that computed from the slope of partitionedw profiles.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Boundary layer meteorology 53 (1990), S. 223-265 
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In the summer of 1988/89 flights were carried out in the Coorong coastal area of South Australia to investigate sea-breeze fronts. The flights yielded data sets of the structure of the fronts in the cross-frontal direction with a spatial resolution of approximately 3 m. The study is focused on the budgets of sensible and latent heat in the vicinity of the front and on frontogenesis/frontolysis processes which are closely related to budget considerations. The frontogenesis relationships and the budgets were established on a 2 km length scale by low-pass filtering of the space series. As the wind components were measured with high accuracy, all processes which determine frontogenesis could be evaluated and are displayed in x,z-cross-sections: these are the confluence, shear and diabatic effects, all of which play a role in ∂q/∂x-, ∂q/∂z-, ∂θ/∂x- as well as ∂θ/∂z-frontogenesis. A detailed analysis is given for two different states of frontal development. The presented results shed much light on the governing physical processes in the frontal region with strong emphasis on the effects of confluence-generated updrafts, on shear instabilities causing bulges and clefts in the frontal surface as well as producing the elevated frontal head, and on processes related to differential heating and moistening.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Boundary layer meteorology 89 (1998), S. 385-405 
    ISSN: 1573-1472
    Keywords: Aircraft measurements ; Atmospheric dispersion ; Coastal meteorology ; Sea breeze ; Shoreline fumigation ; Slab model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Aircraft measurements of potential temperature and turbulent kinetic energy are used to examine the growth of the thermal internal boundary layer (TIBL) in sea-breeze flows on four selected days of a coastal fumigation study performed in 1995 at Kwinana in Western Australia. The aircraft data, together with radiosonde measurements taken on the same days, show a multi-layered low-level onshore flow in the vertical with a superadiabatic layer extending to about 50 m above the water surface on all four days. On the first three days the layer above the superadiabatic layer was neutral, typically 200 m deep, capped by a stably stratified region, whereas on the remaining day it was fully stable. The occurrence of the neutral layer on most experimental days contrasts with the more usual situation involving an entirely stable onshore flow. A composite approach based on both temperature and turbulence data is used to provide a pragmatic but self-consistent definition of the TIBL height. The data for the first three days indicate that the TIBL grows rapidly into the neutrally stratified region to the top of the region within about 2 km from the coast, with a very slow subsequent growth into the stable stratification aloft. On the other hand, the TIBL grows only to about 200 m within a distance of 7 km from the coast on the fourth day due to a strong stable stratification. An existing numerical TIBL model based on the slab approach, capable of describing the TIBL growth in both neutral and stable environments, and a recent analytical model, more efficient for operational use, are used to simulate the aircraft TIBL observations. The predictions by both models agree reasonably well with the data.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Boundary layer meteorology 64 (1993), S. 55-74 
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The processes of interaction between the atmospheric surface and mixed layers in daytime convective conditions over land are studied using a data set obtained during flights by an instrumented aircraft. Profiles of partitioned run-averaged statistics and examples of time series plots are discussed in the light of results from a recently published study by the authors, in which the average structure and flow within coherent eddies was reconstruced using a compositing technique. This evidence is used to support a conceptual model of the mechanisms of interaction between surface-layer plumes and mixed-layer thermal columns. The divergent flow created near the surface by the downdraft arms of the large-scale mixed-layer circulation patterns, forces the development of lines of convergence in the surface layer (the so-called “thermal walls”), which channel air into the bases of the mixed-layer thermals. Plumes progressively group and merge together with height in the surface and free convection layers, and move along these convergence lines toward large “collector” plumes at the intersection points, or “hubs”. Above the “hubs” are the thermals, and air parcels originating from plumes and their environment are strongly mixed as they rise, leading to an increased difficulty of the conditional sampling method to distinguish between them. The observed influence of mixed-layer convective processes far down into the surface layer, and the form of the averaged profiles, supports recent refinements of the theory of surface-layer structure suggested in Kader and Yaglom (1990).
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-1472
    Keywords: Air pollution meteorology ; Aircraft measurements ; Field experiment ; Lidar measurements ; Plume diffusion ; Sea breeze ; Thermal internal boundary layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Fumigation under sea-breeze conditions is a major feature of the air pollution meteorology in the coastal industrial region of Kwinana, south of Perth in Western Australia. An intensive field experiment on fumigation was carried out in the region in early 1995 with the objective of using the measured data to develop and test a shoreline fumigation model. Fumigation of plumes from the Kwinana Power Station was studied using an instrumented research aircraft, radiosonde balloons, meteorological stations, a lidar, a mobile surface sampler, and sonic anemometers. The study has yielded a detailed and high quality data set as a result of both the range of observations undertaken and of the regularity of the sea-breeze conditions under scrutiny. The details of the experiment are summarised in this paper and some typical results are presented.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 70 (1999), S. 81-95 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary  This paper is a contribution to experimental meteorology: A sea-breeze front was investigated by aircraft observations and thorough numerical analysis using an unprecedented number of runs crossing the same front within a timespan of . The 33 runs were flown in a situation of offshore geostrophic wind of 5 m/s in 1000 hPa and with the strategy of obtaining information on the four-dimensional field (t=time, x=cross-coastal coordinate, y=coast-parallel coordinate, z=height): 9 runs in x-direction (and reverse) at different heights to yield x,z-cross-sections of the observed meteorological quantities (specific humidity q, potential temperature Θ and the components u, v and w of the wind velocity), assuming a frozen structure in time; the next 7 runs again in x-direction but all at the same level and on the same track to yield x,t-diagrams of the same quantities in order to study the temporal changes compared to those with x and z; the next 10 runs as a zig-zagging flight track crossing the front but drifting in y-direction, all at the same height, in order to obtain the y-dependency; andfinally 7 runs for another x,z-cross-sectional analysis, which can be compared to that evaluated from the runs at the beginning of the mission. The paper describes the 4-dimensional dependencies in detail. Pure x-variations at constant z are expressed by VCM low-pass filtered space series (VCM=variance conserving multiresolution, according to Howell and Mahrt, 1994). The x,z-analyses are similar to those in Kraus et al. (1990) and Finkele et al. (1995) verifying these results. The comparison of the x,z-studies gained from the data at the beginning and at the end of the mission show how the sea-breeze frontal area changes its structure. The fluctuations (in time) revealed by the low-pass filtered x,t-runs (same track and same height) are smaller than the contour intervals chosen in the x,z-cross-sections. This shows, that the single runs, from which the x,z-cross-sections are constructed, reliably and significantly contribute to the interpolated structure. The paper also demonstrates the overall development of the front within the 31/2 h of continuous observation. The x,y-fields demonstrate that the y-dependency of the various quantities is generally one order of magnitude smaller than the x-dependency and that the assumption of negligible y-dependency holds in the first order of approximation for a fairly homogeneous coast. Convective disturbances of a horizontal scale of 1 to 4 km at the landward side of the front, embedded in the offshore flow and bouncing against the landward propagating sea-breeze front, considerably contribute to variations of the frontal propagation speed and of the frontal shape and also to changes of the parameters with the along-frontal coordinate y.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 73 (2000), S. 157-175 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary In Southern Australia summertime deep cold fronts are frequently preceded by a shallow cold frontal line connected to a prefrontal lower tropospheric trough. The advance of this line defines a “cool change” which in many cases causes severe weather events. The goal of this paper is to analyze the multi-scale structure of these cool changes using aircraft observations and synoptic-scale analyses. The aircraft measurements on cross-frontal tracks of horizontal lengths of up to 300 km are performed with an average resolution of 3 to 4 m along the track. Thus a multi-scale analysis from micro-scale events up to the synoptic-scale phenomena can be presented. All flights and thus all meso- and micro-scale analyses are performed over water only. The obviously very different characteristics of the cool change structure elements over land are not investigated. The synoptic analyses for one very typical case show a prefrontal trough as characterized by its position in relation to the main deep cold front, its source region in Western Australia and its extent to the southeast. Fields of strong wind shear, temperature gradients, vertical wind and Q-vectors are displayed. The meso-β-scale x, z-cross-sections derived from two aircraft missions (data of the second one in brackets) show: a shallow cold front with a 160 (60) km wide transition zone in which the near surface potential temperature drops rather steadily by 9 °C (20 °C); a shallow feeder flow topped by a strong inversion with a vertical gradient of potential temperature up to 5 °C/100 m between the top of the feeder flow at 400 (200) m and 1500 (700) m; a cross-frontal circulation expressed by the ageostrophic wind components u ϕ,subscale and w with a center at 1200 m over the frontal edge of the feeder flow (for one mission only); a strong shear of the along-frontal wind component v ϕ with a large increase of the negative v ϕ-values with height, which very well fits to the synoptic-scale view of the wave structure of the geostrophic wind (well-known from the upper level synoptic charts) at different heights; a jet core of this along-frontal wind in the center of the cross-frontal circulation, again for one mission only. A very striking example of a micro-scale event is an approximately 1 km wide head of a frontal squall line. It shows dramatic changes of all meteorological parameters. The event is displayed in a horizontal domain of 4 km with full resolution (∼ 4 m). Derivatives of the measured parameters in the cross-frontal direction add information to the space series of the parameters themselves. Deformation frontogenesis of potential temperature and specific humidity show very large values on the scale resolved here. Fortunately the squall line could be sampled again at the same height, but in a somewhat degenerated state 1½ h later.
    Type of Medium: Electronic Resource
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  • 8
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    In:  EPIC34th Air-Sea Interaction Conference, Melbourne, 1992, pp. 18-19
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 9
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    In:  EPIC3International journal of remote sensing, ISBN: 0143-1161
    Publication Date: 2019-07-17
    Description: A new low-cost high-resolution line scanner has been developed at theAlfred Wegener Institut for Polar and Marine Research in Germany. ForNDVI applications the Color Line Scanner (CLS) measures the solarradiation reflected by the ground surface in the spectral ranges of500nm to 570nm (green), 580nm to 680nm (red) and 720nm to 830nm(near infrared). With the red and near infrared spectral bands the NDVIcan be calculated in order to map vegetation. The line scanner supportsa resolution of 2048 pixels per line for each spectral band. During dataacquisition 50 lines per second are stored yielding a maximum spatialresolution of better than 0.5m. With DGPS and attitude measurements(INS or Vector GPS) it is possible to geo-reference the line scanner datainto a map format with an absolute accuracy of a few metres. Severalimages can be combined to cover large areas. After the determinationof mounting errors the geo-referencing into a map is carried outautomatically without manual adjustments. The CLS was first used as animaging NDVI sensor at Airborne Research Australia (ARA) the MajorNational Research Facility at the Flinders University of South Australiato investigate spatial and temporal variations of vegetation cover.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 10
    Publication Date: 2017-03-01
    Description: The purpose of the Tropical Air–Sea Propagation Study (TAPS), which was conducted during November–December 2013, was to gather coordinated atmospheric and radio frequency (RF) data, offshore of northeastern Australia, in order to address the question of how well radio wave propagation can be predicted in a clear-air, tropical, littoral maritime environment. Spatiotemporal variations in vertical gradients of the conserved thermodynamic variables found in surface layers, mixing layers, and entrainment layers have the potential to bend or refract RF energy in directions that can either enhance or limit the intended function of an RF system. TAPS facilitated the collaboration of scientists and technologists from the United Kingdom, the United States, France, New Zealand, and Australia, bringing together expertise in boundary layer meteorology, mesoscale numerical weather prediction (NWP), and RF propagation. The focus of the study was on investigating for the first time in a tropical, littoral environment the i) refractivity structure in the marine and coastal inland boundary layers; ii) the spatial and temporal behavior of momentum, heat, and moisture fluxes; and iii) the ability of propagation models seeded with refractive index functions derived from blended NWP and surface-layer models to predict the propagation of radio wave signals of ultrahigh frequency (UHF; 300 MHz–3 GHz), super-high frequency (SHF; 3–30 GHz), and extremely high frequency (EHF; 30–300 GHz). Coordinated atmospheric and RF measurements were made using a small research aircraft, slow-ascent radiosondes, lidar, flux towers, a kitesonde, and land-based transmitters. The use of a ship as an RF-receiving platform facilitated variable-range RF links extending to distances of 80 km from the mainland. Four high-resolution NWP forecasting systems were employed to characterize environmental variability. This paper provides an overview of the TAPS experimental design and field campaign, including a description of the unique data that were collected, preliminary findings, and the envisaged interpretation of the results.
    Print ISSN: 0003-0007
    Electronic ISSN: 1520-0477
    Topics: Geography , Physics
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