Evolution Of Wind Research Articles

Analysis of surface wind and roughness length evolution with fetch using a combination of airborne lidar and radar measurements

A combination of surface wind speed (SWS) and sea state variables, derived from quasi‐simultaneous airborne lidar and radar measurements, made in the framework of the Flux, État de mer et Télédétection en Condition de fetcH variable (FETCH) experiment, is used to analyze the evolution of surface roughness length, neutral drag coefficient, and friction velocity coefficient with fetch in the first hundred kilometers offshore over the Gulf of Lion, Western Mediterranean. The study focuses on the Tramontane/Mistral event documented in the afternoon of 24 March 1998. Particular attention is given to SWS derived from nadir lidar measurements. The SWS retrieval methodology developed and validated for open ocean conditions byFlamant et al.[1998]has been modified to account for the specificity of the coastal Mediterranean environment (complex mixture of continental and maritime aerosol; turbid, productive waters). The lidar‐derived SWS evolution with fetch observed on 24 March 1998 in the afternoon was validated against in situ and remote sensing measurements made from a buoy, a ship, as well as from the spaceborne altimeter TOPEX. The spatial variability in SWS observed with the airborne lidar was controlled by the structure of the wake regions downstream of the Massif Central and the Maritime Alps, delimiting the longitudinal extension of the Mistral, and was influenced by swell resulting from the action of a steady northeasterly flow coming from the Ligurian Sea in connection with intense Alpine lee cyclogenesis. These findings were supported by the other measurements. It is further shown that, based on a formulation of the dimensionless roughness dependance with wave age, airborne lidar and radar measurements can be combined to provide insight into the evolution with fetch of roughness length, neutral drag coefficient, and friction velocity. Four distinct sea state regimes over a distance of 100 km could be identified from the remotely sensed variables obtained with this novel approach in connection with atmospheric forcing. The dependance of lidar/radar derived drag coefficient with lidar‐derived SWS for the four regimes was found to be remarkably consistent with the relationship derived from the buoy measurements. Finally, lidar/radar derived friction velocities were found in good agreement with the buoy and in situ aircraft measurements.

MHD Models and Laboratory Experiments of Jets

Jet research has long relied upon a combination of analytical, observational and numerical studies to elucidate the complex phenomena involved. One element missing from these studies (which other physical sciences utilize) is the controlled experimental investigation of such systems. With the advent of high-power lasers and fast Z-pinch machines it is now possible to experimentally study similar systems in a laboratory setting. Such investigations can contribute in two useful ways. They can be used for comparison with numerical simulations as a means to validate simulation codes. More importantly, however, such investigations can also be used to complement other jet research, leading to fundamentally new knowledge. In the first part of this article, we analyze the evolution of magnetized wide-angle winds in a collapsing environment. We track the ambient and wind mass separately and describe a physical mechanism by which an ionized central wind can entrain the ambient gas giving rise to internal shells of molecular material on short time scales. The formation of internal shells in molecular outflows has been found to be an important ingredient in describing the observations of convex spurs in P-V diagrams (Hubble wedges in M-V diagrams). In the second part, we present astrophysically relevant experiments in which supersonic jets are created using a conical wire array Z-pinch. The conically convergent flow generates a standing shock around the axis which collimates the flow into a Mach ∼ 30 jet. The jet formation process is closely related to the work of Canto et al. (1988) for hydrodynamic jet collimation. The influence of radiative cooling on collimation and stability is studied by varying the wire material (A1, Fe, and W).

Comparison of the effects of wave-particle interactions and the kinetic suprathermal electron population on the acceleration of the solar wind

Kinetic effects due to wave-particle interactions and suprathermal electrons have been suggested in the literature as possible solar wind acceleration mechanisms. Ion cyclotron resonant heating, in particular, has been associated with some qualitative features observed in the solar wind. In terms of solar wind acceleration, however, it is interesting to compare the kinetic effects of suprathermal electrons with those due to the wave-particle interactions. The combined effects of the two acceleration mechanisms on the fast solar wind have been studied by Tam and Chang (1999a,b). In this study. we investigate the role of the suprathermal electron population in the acceleration of the solar wind. Our model follows the global kinetic evolution of the fast solar wind under the influence of ion cyclotron resonant heating, while taking into account Coulomb collisions, and the ambipolar electric field that is consistent with the particle distributions themselves. The kinetic effects due to the suprathermal electrons, which we define to be the tail of the electron distributions, can be included in the model as an option. By comparing the results with and without the inclusion of the suprathermal electron effects, we determine the relative importance of suprathermal electrons and wave-particle interactions in driving the solar wind. We find that although suprathermal electrons enhance the ambipolar electric potential in the solar wind considerably, their overall influence as an acceleration mechanism is relatively insignificant in a wave-driven solar wind.

Simulations of fall and early winter in the stratosphere

Mechanistic model simulations of fall/early winter in the northern (November and December) and southern (May and June) stratosphere are compared with observational analyses to examine the skill of the model in simulating the state of the stratosphere, including both means and variability in key fields, during six winters. While detailed success varies from year to year, the model produces a realistic climatology of and variability in the evolution of winds, geopotential heights, temperatures and wave propagation in the early-winter stratosphere. The variability and mean fields agree well with those in longer data records. The northern hemisphere (NH) simulations show a small cold bias when averaged over the 6 years, while the southern hemisphere (SH) simulations show a larger warm bias. Greater detailed success in simulations of alternate NH winters suggests the possibility of greater model skill during the westerly quasi-biennial oscillation phase, although the short record and complexity of interactions between tropics and high latitudes preclude definitive identification of such a relationship. A prominent failing of the model when using Rayleigh friction to parametrize gravity-wave drag is an inability to correctly reproduce the latitudinal structure of the stratospheric jet above about 7 hPa; this failing can be alleviated by using a non-orographic gravity-wave drag parametrization, at the expense of frequently degrading agreement of planetary-wave phases and amplitudes. The success of the model in reproducing realistic climatology and variability makes these simulations useful for more detailed studies of transport and vortex evolution in early winter. Interhemispheric comparisons show that the early-winter circulations are qualitatively similar in the NH and SH: they are dominated by a strengthening vortex, with most wave activity being in wave 1; they both have minor warmings in a preferred location and clustered around a preferred time—early December (early June) in the NH (SH); variability in the flow shows a crescent pattern of maximum variations near 60–80° latitude centred at the location of the minor warmings (over the dateline in the NH and in the South Pacific in the SH). Interhemispheric differences are primarily in the magnitude of the variability, with a more symmetric circulation and weaker minor warmings in the SH; this is in contrast to later in the winter, when large qualitative interhemispheric differences have been seen. Copyright © 2002 Royal Meteorological Society

Radio Emission from Supernovae and Gamma-Ray Bursters

▪ Abstract Study of radio supernovae over the past 20 years includes two dozen detected objects and more than 100 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the stellar system, and to show clumpiness of the circumstellar material. More speculatively, it may be possible to provide distance estimates to radio supernovae. Over the past four years the afterglow of gamma-ray bursters has occasionally been detected in the radio, as well in other wavelengths bands. In particular, the interesting and unusual gamma-ray burst GRB980425, thought to be related to SN1998bw, is a possible link between supernovae and gamma-ray bursters. Analyzing the extensive radio emission data avaliable for SN1998bw, one can describe its time evolution within the well-established framework available for the analysis of radio emission from supernovae. This allows relatively detailed description of a number of physical properties of the object. The radio emission can best be explained as the interaction of a mildly relativistic (Γ ∼ 1.6) shock with a dense preexplosion stellar wind–established circumstellar medium that is highly structured both azimuthally, in clumps or filaments, and radially, with observed density enhancements. Because of its unusual characteristics for a Type Ib/c supernova, the relation of SN1998bw to GRB980425 is strengthened and suggests that at least some classes of GRBs originate in massive star explosions. Thus, employing the formalism for describing the radio emission from supernovae and following the link through SN1998bw/GRB980425, it is possible to model the gross properties of the radio and optical/infrared emission from the half-dozen GRBs with extensive radio observations. From this we conclude that at least some members of the “slow-soft” class of GRBs can be attributed to the explosion of a massive star in a dense, highly structured circumstellar medium that was presumably established by the preexplosion stellar system.

Late Cretaceous to early Quaternary organic sedimentation in the eastern Equatorial Atlantic

Reconstructing the long-term evolution of organic sedimentation in the eastern Equatorial Atlantic (ODP Leg 159) provides information about the history of the climate/ocean system, sediment accumulation, and deposition of hydrocarbon-prone rocks. The recovery of a continuous, 1200 m long sequence at ODP Site 959 covering sediments from Albian (?) to the present day (about 120 Ma) makes this position a key location to study these aspects in a tropical oceanic setting. New high resolution carbon and pyrolysis records identify three main periods of enhanced organic carbon accumulation in the eastern tropical Atlantic, i.e. the late Cretaceous, the Eocene–Oligocene, and the Pliocene–Pleistocene. Formation of Upper Cretaceous black shales off West Africa was closely related to the tectono-sedimentary evolution of the semi-isolated Deep Ivorian Basin north of the Côte d’Ivoire–Ghana Transform Margin. Their deposition was confined to certain intervals of the last two Cretaceous anoxic events, the early Turonian OAE2 and the Coniacian–Santonian OAE3. Organic geochemical characteristics of laminated Coniacian–Santonian shales reveal peak organic carbon concentrations of up to 17% and kerogen type I/II organic matter, which qualify them as excellent hydrocarbon source rocks, similar to those reported from other marginal and deep sea basins. A middle to late Eocene high productivity period occurred off equatorial West Africa. Porcellanites deposited during that interval show enhanced total organic carbon (TOC) accumulation and a good hydrocarbon potential associated with oil-prone kerogen. Deposition of these TOC-rich beds was likely related to a reversal in the deep-water circulation in the adjacent Sierra Leone Basin. Accordingly, outflow of old deep waters of Southern Ocean origin from the Sierra Leone Basin into the northern Gulf of Guinea favored upwelling of nutrient-enriched waters and simultaneously enhanced the preservation potential of sedimentary organic matter along the West African continental margin. A pronounced cyclicity in the carbon record of Oligocene–lower Miocene diatomite–chalk interbeds indicates orbital forcing of paleoceanographic conditions in the eastern Equatorial Atlantic since the Oligocene–Miocene transition. A similar control may date back to the early Oligocene but has to be confirmed by further studies. Latest Miocene–early Pliocene organic carbon deposition was closely linked to the evolution of the African trade winds, continental upwelling in the eastern Equatorial Atlantic, ocean chemistry and eustatic sea level fluctuations. Reduction in carbonate carbon preservation associated with enhanced carbon dissolution is recorded in the uppermost Miocene (5.82–5.2 Ma) section and suggests that the latest Miocene carbon record of Site 959 documents the influence of corrosive deep waters which formed in response to the Messinian Salinity Crisis. Furthermore, sea level-related displacement of higher productive areas towards the West African shelf edge is indicated at 5.65, 5.6, 5.55, 5.2, 4.8 Ma. In view of humid conditions in tropical Africa and a strong West African monsoonal system around the Miocene–Pliocene transition, the onset of pronounced TOC cycles at about 5.6 Ma marks the first establishment of upwelling cycles in the northern Gulf of Guinea. An amplification in organic carbon deposition at 3.3 Ma and 2.45 Ma links organic sedimentation in the tropical eastern Equatorial Atlantic to the main steps of northern hemisphere glaciation and testifies to the late Pliocene transition from humid to arid conditions in central and western African climate. Aridification of central Africa around 2.8 Ma is not clearly recorded at Site 959. However, decreased and highly fluctuating carbonate carbon concentrations are observed from 2.85 Ma on that may relate to enhanced terrigenous (eolian) dilution from Africa.

Mechanisms of Antarctic katabatic currents near Terra Nova Bay

The evolution of Antarctic katabatic wind in the vicinity of Terra Nova Bay has been studied using a three-dimensional, hydrostatic, limited area model. Realistic simulations of a summer katabatic event, using different horizontal resolutions, have been performed by employing a sequential self-nesting procedure. The high-resolution orography data allow a description of the structure of the main valleys and of the two different flows descending from the broad Reeves Glacier and (with less accuracy) channelled into the much narrower Priestley Glacier valley, respectively. The mechanism of katabatic wind development has been investigated by means of a Lagrangian diagnostic study performed along trajectories flowing down from the above-mentioned glaciers. Heat balance and kinetic energy balance have been evaluated accurately in order to asses the characteristics of the two katabatic currents that may superpose once they reach the Nansen Ice Sheet.

Mechanisms of Antarctic katabatic currents near Terra Nova Bay

The evolution of Antarctic katabatic wind in the vicinity of Terra Nova Bay has been studiedusing a three-dimensional, hydrostatic, limited area model. Realistic simulations of a summerkatabatic event, using different horizontal resolutions, have been performed by employing asequential self-nesting procedure. The high-resolution orography data allow a description ofthe structure of the main valleys and of the two different flows descending from the broadReeves Glacier and (with less accuracy) channelled into the much narrower Priestley Glaciervalley, respectively. The mechanism of katabatic wind development has been investigated bymeans of a Lagrangian diagnostic study performed along trajectories flowing down from theabove-mentioned glaciers. Heat balance and kinetic energy balance have been evaluated accuratelyin order to asses the characteristics of the two katabatic currents that may superpose oncethey reach the Nansen Ice Sheet.

Thermal Emission Spectrometer results: Mars atmospheric thermal structure and aerosol distribution

Infrared spectra returned by the Thermal Emission Spectrometer (TES) are well suited for retrieval of the thermal structure and the distribution of aerosols in the Martian atmosphere. Combined nadir‐ and limb‐viewing spectra allow global monitoring of the atmosphere up to 0.01 mbar (65 km). We report here on the atmospheric thermal structure and the distribution of aerosols as observed thus far during the mapping phase of the Mars Global Surveyor mission. Zonal and temporal mean cross sections are used to examine the seasonal evolution of atmospheric temperatures and zonal winds during a period extending from northern hemisphere midsummer through vernal equinox (Ls = 104°–360°). Temperature maps at selected pressure levels provide a characterization of planetary‐scale waves. Retrieved atmospheric infrared dust opacity maps show the formation and evolution of regional dust storms during southern hemisphere summer. Response of the atmospheric thermal structure to the changing dust loading is observed. Maps of water‐ice clouds as viewed in the thermal infrared are presented along with seasonal trends of infrared water‐ice opacity. Uses of these observations for diagnostic studies of the dynamics of the atmosphere are discussed.

Polar observations and model predictions during May 4, 1998, magnetopause, magnetosheath, and bow shock crossings

During the rise to the maximum phase of solar cycle 23, several periods of extreme solar wind conditions have occurred. During such an example on May 4, 1998, the solar wind monitors observed a period of strong southward interplanetary magnetic field (IMF) accompanied by a solar wind dynamic pressure that was 30 times higher than average. During this period the Polar spacecraft crossed the magnetopause and bow shock and experienced its first solar wind encounter. This case provides a rare opportunity to study the magnetopause, low‐latitude boundary layer, magnetosheath, and bow shock and to test our ability to model the dynamic behavior of these boundary regions under extreme and highly variable solar wind conditions. In this study we use the gas dynamic convected field model to predict the time‐dependent magnetic field and plasma properties upstream from the magnetopause and the location of the Polar spacecraft relative to the magnetopause and bow shock during the event. To test the accuracy of the prediction, model magnetic field characteristics are compared to the fields observed along the satellite track by the magnetometer on Polar. The predicted model plasma characteristics (density, velocity, and temperature) are compared to moments derived from TIDE observations, extrapolated to account for the higher energy portion of the magnetosheath distributions. Where ambiguities occur in identifying the satellite location, plasma distribution functions from two additional ion detectors (TIMAS and HYDRA) are used to resolve the observed location of Polar relative to the boundaries. With this procedure, carried out separately for ACE and Wind and for two different magnetopause models, observed features at Polar can be traced back to drivers in the solar wind, providing a unique opportunity to assess the evolution of the solar wind and its predictability from the solar wind monitors to the magnetopause. When the Polar apogee drifts to low latitudes in the future, it will provide more and more observations in this region. Therefore what we learn from this case can be indicative of what we will see in the future in Polar operations. The high‐level correlation between the predictions and in situ measurements indicates that the solar wind monitors often provide adequate and useful solar wind conditions near the Earth. The tests indicate that in this event the vacuum dipole field magnetosphere model predicts a significantly larger magnetosphere than observed. While the empirical magnetopause model predictions are more consistent with the observations, they overpredict the response of the magnetosphere to transient southward turnings of the IMF, indicating that the magnetosphere does not respond to the southward IMF turnings on small timescales. Sometimes, there are significant differences at relatively small time scales between the measurements from the two solar wind monitors. It is possible for the solar wind conditions near the Earth to be different from the measurements made by at least one of the solar wind monitors. Cautions should be taken when interpreting near‐Earth observations if the observations are inconsistent at small timescales with the predictions based on one solar wind monitor.

Upwelling along the coasts of Java and Sumatra and its relation to ENSO

Upwelling along the Java‐Sumatra Indian Ocean coasts is a response to regional winds associated with the monsoon climate. The upwelling center with low sea surface temperature migrates westward and toward the equator during the southeast monsoon (June to October). The migration path depends on the seasonal evolution of alongshore winds and latitudinal changes in the Coriolis parameter. Upwelling is eventually terminated due to the reversal of winds associated with the onset of the northwest monsoon and impingement of Indian Ocean equatorial Kelvin waves. Significant interannual variability of the Java‐Sumatra upwelling is linked to ENSO through the Indonesian throughflow (ITF) and by anomalous easterly wind. During El Niño episodes, the Java‐Sumatra upwelling extends in both time (into November) and space (closer to the equator). During El Nino (La Niña), the ITF carries colder (warmer) water shallowing (deepening) thermocline depth and enhancing (reducing) upwelling strength.

Effect of electron resonant heating on the kinetic evolution and acceleration of the solar wind

We investigate the effects of electron cyclotron resonant heating on the kinetic evolution and acceleration of the fast solar wind. A previous study has shown that kinetic wave‐particle interactions due to ion resonant heating, may account for the bulk acceleration of the solar wind, the preferential heating of the helium ions over the protons, as well as the occasionally observed double‐peaked proton velocity distributions. The model followed the evolution of the particle distributions along an inhomogeneous field line under the effects of ion heating, Coulomb collisions, and an ambipolar electric field that was consistent with the distributions themselves. This study extends the model to take into account also the effect of electron cyclotron resonant heating. Our parametric study shows that the electron heating does not change the solar wind qualitative features described above. However, the wave‐particle interaction increases the ambipolar electric field, thereby enhancing the solar wind velocity.

Micrometeorological simulations over a complex terrain with SUBMESO: a model study using a novel pre-processor

Effects of topography on micrometeorological fields may have a great impact on noise propagation. Consequently, we discuss some preliminary results from a modelling study of short-term evolution of wind and temperature over a smooth, non-flat terrain. The study is performed using the 3-D model SUBMESO. A new meteorological pre-processor (MPP) has been implemented to specify vertical profiles of wind, temperature and other scalar quantities, which can be used to drive the flow and set the model reference state. Numerical simulations have been performed in strongly convective and neutral shear-driven conditions. We obtain results similar to those from reference simulations over flat terrain and ascertain that the small-scale topography modifies the mean flow and the structure of the instantaneous velocity field in both cases. Unlike what is expected for stable stratification, no channelling effect is visible for the atmospheric conditions considered here. This study is a first validation of the MPP device.

A Large Eddy Simulation Study of a Quasi-Steady, Stably Stratified Atmospheric Boundary Layer

Using the large eddy simulation (LES) technique, the authors study a clear-air, stably stratified atmospheric boundary layer (ABL) as it approaches a quasi-steady state. The Beaufort Sea Arctic Stratus Experiment (BASE) dataset is used to impose initial and boundary conditions. The authors explore the parameter space of the boundary layer by varying latitude, surface cooling rate, geostrophic wind, inversion strength, and surface roughness. Recognizing the critical dependence of the results of LES on the subgrid-scale (SGS) model, they test and use a nonlinear SGS model, which is capable of reproducing the effects of backscatter of turbulent kinetic energy (TKE) and of the SGS anisotropies characteristic for shear-driven flows. In order to conduct a long-term LES so that an ABL can reach a quasi-steady state, a parallel computer code is developed and simulations with a spatial domain of up to 963 grid points are performed. The authors analyze the evolution of the mean wind, potential temperature, and turbulence profiles as well as the turbulence budgets. In their simulations, they observe the development of features that are characteristic of a stably stratified ABL: a two-layer ABL structure, an elevated inversion, and an associated inversion wind maxima. Good agreement is found between the LES results and the observations and with Nieuwstadt’s analytical model. The authors study the dependence of the boundary layer height on the flow parameters and determine model coefficients for a truncated Zilitinkevich–Mironov model.

An Example of a Network—Based Approach to Data Access, Visualization, Interactive Analysis, and Distribution

A freely available software package, called Web Winds, has been developed that allows atmospheric scientists, educators, students, and the general public to quickly and easily visualize and analyze data on many of the computer platforms in use today. Web Winds is written in Java and is able to ingest files from local disk or the World Wide Web (WWW). It is designed to eventually be distributed over the Internet and operate outside of WWW browsers entirely, allowing fewer restrictions as to where data and applications will be required to be stored. By manipulating data at their source, Internet bandwidth requirements will be reduced. The design and evolution of Web Winds, including its current display and analysis capabilities, security considerations, collaborative tools, availability, and planned future developments are described. Two typical sessions are also described to give the reader an introduction to its use.

A numerical study of the evolution of the solar wind from Ulysses to Voyager 2

Voyager 2 continues to explore the outer heliosphere as Ulysses studies the latitudinal dependence of the solar wind. During the year 1991 these spacecraft were within 2° latitude and their radial separation was larger than 30 AU. This alignment presents a good opportunity to investigate the evolution of the solar wind and, in particular, the effect of pickup ions, which are an important component of the solar wind in the outer heliosphere. A numerical simulation study is used to model the evolution of solar wind structures from the location of Ulysses (1–5 AU) to Voyager 2 (33–36 AU) in 1991. The Ulysses observations were used as input into the numerical models and the theoretical predictions were compared with the Voyager 2 observations. The model produces profiles and magnitudes of the plasma parameters (e.g., flow speed and density) which are in reasonable agreement with the observations. The inclusion of pickup ions slows the solar wind, reduces the amplitudes of the speed variations and density spikes, and changes the speed of shock propagation. However, within 35 AU, pickup ions do not change the solar wind structures dramatically. Our calculations favor a low interstellar neutral hydrogen density, i.e., nH∞ = 0.05 cm−3, for this time period (1991).

A numerical study of the evolution of the solar wind from Ulysses to Voyager 2

A numerical study of the evolution of the solar wind from Ulysses to Voyager 2

Galactic winds and circulation of the interstellar medium in dwarf galaxies

We study, through 2D hydrodynamical simulations, the feedback of a starburst on the ISM of typical gas-rich dwarf galaxies. The main goal is to address the circulation of the ISM and metals following the starburst. We assume a single-phase rotating ISM in equilibrium in the galactic potential generated by a stellar disc and a spherical dark halo. The starburst is assumed to occur in a small volume in the centre of the galaxy, and it generates a mechanical power of 3.8×1039 or 3.8×1040 erg s−1 for 30 Myr. We find, in accordance with previous investigations, that the galactic wind is not very effective in removing the ISM. The metal-rich stellar ejecta, however, can be efficiently expelled from the galaxy and dispersed in the intergalactic medium. Moreover, we find that the central region of the galaxy is always replenished with cold and dense gas a few 100 million years after the starburst, achieving the requisite for a new star formation event in ≈0.5–1 Gyr. The hydrodynamical evolution of galactic winds is thus consistent with the episodic star formation regime suggested by many chemical evolution studies. We also discuss the X-ray emission of these galaxies and find that the observable (emission-averaged) abundance of the hot gas underestimates the real one if thermal conduction is effective. This could explain the very low hot-gas metallicities estimated in starburst galaxies.

Kinetic evolution and acceleration of the solar wind

We investigate the effects of kinetic wave‐particle interactions on the solar wind using a global hybrid model. The model follows the evolution of the particle distributions along an inhomogeneous field line under the influence of wave‐particle interactions, an am‐bipolar electric field that is consistent with the particle distributions themselves, and Coulomb collisions. This represents the “first results” of global evolutionary study of the solar wind that take into account these kinetic effects. The model can account for the bulk acceleration of the solar wind, the preferential heating of the helium ions over the protons, as well as the occasionally observed double‐peaked proton velocity distributions.

Diurnal Variations of the Temperature and Their Influenceon Wind Regime in a Confluence Zone of Antarctica

The behaviour of the wind field at the confluence zone of Terra Nova Bay during a transition period from winter to summer is considered. To explain some observed features the influence of diurnal variations are considered to integrate and complete the analysis based on annual and seasonal variations. Diurnal variations in the buoyancy difference between two main air masses coming from the Revees and Priestley glaciers are assumed to contribute to diurnal alteration of the wind direction at the Nansen ice sheet. The data recorded at three automatic weather stations (AWS) available that period are analysed. Using the wavelet analysis procedure, it is shown that the contribution of one-day variations of some basic meteorological parameters and their gradients (in particular of temperature and pressure) is important and comparable with synoptic ones. On the base of the diurnal variations some aspects of the local circulation have been explained. The basis for the further studies related to the evolution of katabatic winds in this area are also presented.