Search

The European Space Agency (ESA) wind mission, Aeolus, hosts the first space-based Doppler Wind Lidar (DWL) world-wide. The primary mission objective is to demonstrate the DWL technique for measuring wind profiles from space, intended for assimilation in Numerical Weather Prediction (NWP) models. The wind observations will also be used to advance atmospheric dynamics research and for evaluation of climate models. Mission spin-off products are profiles of cloud and aerosol optical properties. Aeolus was launched on 22 August 2018, and the Atmospheric LAser Doppler INstrument (Aladin) instrument switch-on was completed with first high energy output in wind mode on 4 September 2018 [1], [2]. The on-ground data processing facility worked excellent, allowing L2 product output in near-real-time from the start of the mission. First results from the wind profile product (L2B) assessment show that the winds are of very high quality, with random errors in the free Troposphere within (cloud/aerosol backscatter winds: 2.1 m/s) and larger (molecular backscatter winds: 4.3 m/s) than the requirements (2.5 m/s), but still allowing significant positive impact in first preliminary NWP impact experiments. The higher than expected random errors at the time of writing are amongst others due to a lower instrument out-and input photon budget than designed. The instrument calibration is working well, and some of the data processing steps are currently being refined to allow to fully correct instrument alignment related drifts and elevated detector dark currents causing biases in the first data product version. The optical properties spin-off product (L2A) is being compared e.g. to NWP model clouds, air quality model forecasts, and collocated ground-based observations. Features including optically thick and thin particle and hydrometeor layers are clearly identified and are being validated.

The definition of an atmospheric database is an important component of simulation studies in preparation of future earth observing remote sensing satellites. The Aeolus mission, formerly denoted Atmospheric Dynamics Mission (ADM) or ADM-Aeolus, is scheduled for launch end of 2013 and aims at measuring profiles of single horizontal line-of-sight (HLOS) wind components from the surface up to about 32 km with a global coverage. The vertical profile resolution is limited but may be changed during in-orbit operation. This provides the opportunity of a targeted sampling strategy, e.g., as a function of geographic region. Optimization of the vertical (and horizontal) sampling strategy requires a characterization of the atmosphere optical and dynamical properties, more in particular the distribution of atmospheric particles and their correlation with the atmospheric dynamics. The Aeolus atmospheric database combines meteorological data from the ECMWF model with atmosphere optical properties data from CALIPSO. An inverse algorithm to retrieve high-resolution particle backscatter from the CALIPSO level-1 attenuated backscatter product is presented. Global weather models tend to underestimate atmospheric wind variability. A procedure is described to ensure compatibility of the characteristics of the database winds with those from high-resolution radiosondes. The result is a high-resolution database of zonal, meridional and vertical wind, temperature, specific humidity and particle and molecular backscatter and extinction at 355 nm laser wavelength. This allows the simulation of small-scale atmospheric processes within the Aeolus observation sampling volume and their impact on the quality of the retrieved HLOS wind profiles. The database extends over four months covering all seasons. This allows a statistical evaluation of the mission components under investigation. The database is currently used for the development of the Aeolus wind processing, the definition of wind calibration strategies and the optimization of the Aeolus sampling strategy.

Oblique pellet injection experiments have been performed in RTP ohmic and electron cyclotron (EC) heated plasmas. Peripheral cooling induces a transient rise of the electron temperature (ir,) in the plasma core, with the formation of a region of a high T-e gradient (transient transport barrier). The position of the barrier appears to be linked with the location of low-order rational magnetic surfaces. For Ohmic and EC heated plasmas with resonance moderately off-axis, the T-e rise is peaked in the plasma centre and the footpoint of the barrier is located close to the q = 2 surface. For EC plasmas with far off-axis resonance, i.e. in plasmas exhibiting hollow T-e profiles, the T-e rise starts off-axis, near the innermost low order rational surface (typically q = 3). It then propagates to the centre in a seemingly diffusive way.

Experiments with strong localized electron cyclotron heating (ECH) in the RTP tokamak show that electron heat transport is governed by alternating layers of good and bad thermal conduction. For central deposition hot T-e filaments are observed inside the q = 1 radius. Moving the ECH resonance from the centre to the edge of the plasma results in discrete steps of the central electron temperature. The transitions occur when the minimum q value crosses q = 1, 2, 5/2 or 3, and correspond to the loss of a transport barrier situated close to the rational q value. Close to the transitions a new type of sawtooth activity is observed, characterized by the formation of sharp off-axis maxima on the T, profile, which collapse abruptly. The formation of the off-axis maxima is attributed to heat deposition precisely 'on top of' a transport barrier.

The contents are described of an international pellet ablation database (IPADBASE) that has been assembled to enable studies of pellet ablation theories that are used to describe the physics of an ablating fuel pellet in a tokamak plasma. The database represents an international effort to assemble data from several tokamaks of different magnetic configurations and auxiliary heating methods. In the initial configuration, data from JET, Tore Supra, DIII-D, FTU, TFTR, ASDEX Upgrade, JIPP T-IIU, RTP and T-10 have been included. The database contains details of measurements of deuterium and hydrogen pellet ablation, including pellet mass and speed, plasma electron density and temperature profiles, and pellet ablation light emission. A summary of the database contents and a scaling analysis of the data are presented

The definition of an atmospheric database is an important component of simulation studies in preparation of future earth observing remote sensing satellites. The ADM-Aeolus mission, scheduled for launch in medium 2012, aims at measuring wind profiles from the surface up to about 32 km with a global coverage. The vertical profile resolution is limited but may be changed during in-orbit operation. This provides the opportunity of a targeted sampling strategy, e.g., as a function of geographic region. Optimization of the vertical (and horizontal) sampling strategy requires a characterization of the atmosphere optical and dynamical properties, more in particular the distribution of atmospheric particles and their correlation with the atmospheric dynamics. The ADM-Aeolus atmospheric database combines meteorological data from the ECMWF model with atmosphere optical properties data from CALIPSO. An inverse algorithm to retrieve high-resolution particle backscatter from the CALIPSO level-1 attenuated backscatter product is presented. Global weather models tend to underestimate atmospheric wind variability. A procedure is described to ensure compatibility of the characteristics of the database winds with those from high-resolution radiosondes. The result is a high-resolution database of zonal, meridional and vertical wind, temperature, specific humidity and particle and molecular backscatter and extinction at 355 nm laser wavelength. This allows the simulation of small-scale atmospheric processes within the Aeolus observation sampling volume and their impact on the quality of the retrieved wind profiles. The database extends over four months covering all seasons. This allows a statistical evaluation of the mission components under investigaton. The database is currently used for the development of the ADM-Aeolus wind processing, the definition of wind calibration strategies and the optimization of the Aeolus sampling strategy.

International audience; The climatology of atmospheric horizontal wind and its vertical gradient, i.e., wind shear, is characterized as a function of climate region. For a better representation of the average atmospheric wind and shear and their variabilities, high-resolution radiosonde wind profiles up to about 30 km altitude are compared with the collocated operational ECMWF model for short-range forecast winds. Statistics of zonal and meridional winds are established from both data sets. The results show mainly similarity in the probability distributions of the modeled and observed horizontal winds, practically at all levels of the atmosphere, while at the same time the vertical shear of the wind is substantially underestimated in the model. The comparison of shear statistics of radiosonde and ECMWF model winds shows that the model wind shear mean and variability are on average a factor of 2.5 (zonal) and 3 (meridional) smaller than of radiosondes in the free troposphere, while in the stratosphere, the planetary boundary layer results are more variable. By applying vertical averaging to the radiosonde data, it is found that the effective vertical resolution of the ECMWF model is typically 1.7 km. Moreover, it is found for individually collocated radiosonde model wind and shear profiles that the model wind may lack in some cases variability larger than 5 m s -1 and 0.015 s-1, respectively, due mainly to the effect of lacking vertical resolution, in particular near the jets. Besides the general importance of this study in highlighting the difference in the representation of the atmospheric wind shear by model and observations, it is more specifically relevant for the future Atmospheric Dynamics Mission (ADM-Aeolus) of the European Space Agency due for launch in 2012. The results presented here are used to generate a realistic global atmospheric database, which is necessary to conduct simulations of the Aeolus Doppler wind lidar in order optimize its vertical sampling and processing. © Copyright 2010 by the American Geophysical Union.

An overview of experimental transport studies performed on the Rijnhuizen Tokamak Project (RTP) using transient transport techniques in both Ohmic and ECH dominated plasmas is presented. Modulated Electron Cyclotron Heating (ECH) and oblique pellet injection (OPI) have been used to induce electron temperature (Te) perturbations at different radial locations. These were used to probe the electron transport barriers observed near low order rational magnetic surfaces in ECH dominated steady-state RTP plasmas. Layers of inward electron heat convection in off-axis ECH plasmas were detected with modulated ECH. This suggests that RTP electron transport barriers consist of heat pinch layers rather than layers of low thermal diffusivity. In a different set of experiments, OPI triggered a transient rise of the core Te due to an increase of the Te gradient in the 1

In the Rijnhuizen Tokamak Project (RTP) plasmas with electron cyclotron heating (ECH), a transient rise of the core T-e is observed when hydrogen pellets are injected tangentially to induce fast cooling of the peripheral region. The core T-e rise is a sharp function of the normalized power deposition radius (rho (dep)). The strongest effect (deltaT(e) up to 80%) is observed when rho (dep) is just inside the q = 1 surface, whereas only modest effects are seen with larger or smaller rho (dep). The rise is due to both a steepening of the T-e profile between the q = 1 and q = 2 surfaces, and a peaking inside rho (dep).

A 'non-local' response of the plasma core triggered by peripheral plasma perturbations other than laser ablation is found in the RTP tokamak. Oblique pellet injection (OPI) has been used to induce fast cooling of the peripheral plasma. In response, an inward cold pulse (T-e drop) and a slightly delayed core T-e rise are observed. A somewhat similar 'non-local' response is observed when the peripheral plasma is heated by modulated electron cyclotron heating or by fast current ramps, i.e. the core temperature drops in response to the peripheral heating. The plasma conditions for the occurrence of the 'non-local' response have been investigated. The core T-e rise following OPI is associated with the formation of a large temperature gradient in the region 1 < q < 2. The T-e rise is largest at low electron density and for large pellet deposition radii. Above a critical density the T-e rise disappears and only the (weaker) drop in core T-e is observed. Time dependent transport simulations show that the propagation of the inward cold pulse is consistent with local transport, while the core T-e rise is a slower phenomenon requiring a large transient drop of chi(e) in the region 1 < q < 2. A 'non-local' response of the plasma core triggered by peripheral plasma perturbations other than laser ablation is found in the RTP tokamak. Oblique pellet injection (OPI) has been used to induce fast cooling of the peripheral plasma. In response, an inward cold pulse (Te drop) and a slightly delayed core Te rise are observed. A somewhat similar 'non-local' response is observed when the peripheral plasma is heated by modulated electron cyclotron heating or by fast current ramps, i.e. the core temperature drops in response to the peripheral heating. The plasma conditions for the occurrence of the 'non-local' response have been investigated. The core Te rise following OPI is associated with the formation of a large temperature gradient in the region 1 < q < 2. The Te rise is largest at low electron density and for large pellet deposition radii. Above a critical density the Te rise disappears and only the (weaker) drop in core Te is observed. Time dependent transport simulations show that the propagation of the inward cold pulse is consistent with local transport, while the core Te rise is a slower phenomenon requiring a large transient drop of χe in the region 1 < q < 2.

In the Rijnhuizen Tokamak Project plasmas, a transient rise of the core electron temperature is observed when hydrogen pellets are injected tangentially to induce fast cooling of the peripheral region. High-resolution Thomson scattering measurements show that the T-e rise is associated with large temperature gradients in the region 1 < q < 2. This region acts as a layer of transiently increased thermal resistivity (transport barrier) when probed by fast heat pulses from modulated electron cyclotron heating.

Pellet ablation in the Rijnhuizen Tokamak Project has been studied with an array of 16 fibers viewing the pellet trajectory along very narrow lines of sight. Rapid backward drift of the ablation cloud away from the pellet was observed. This has implications for the determination of the fueling profile and the penetration of the pellet in the plasma. Furthermore, this movement of the ablation cloud offers a new explanation for the often observed striations in the light emission. In contrast to the picture of the pellet periodically leaving the ablation cloud, the ablation cloud moves periodically away from the pellet. [S0031-9007(99)08796-7].

___

We have applied the method of single-atom trajectories to study the mechanism behind some cooling schemes in laser cooling. In several cases we recognize the cooling mechanism as being due to a Sisyphus process, in which the atoms move in a spatially varying light-shift potential and are optically pumped toward the most light-shifted states. In other cases we identify a Sisyphus process in time, in which the light shift is constant and the force on the atom alternates between positive and negative. This process is interrupted by quantum jumps at random instants, and in each case we depict the mechanism leading to a cooling force on the atom. In the special case of sub-Doppler laser cooling in a strong magnetic field we obtain 12 jump operators and identify the jump operators responsible for the cooling. The versatility of the single-atom trajectory method permits it to be applied to any cooling process, and therefore it is a valuable tool in unraveling the physical mechanisms behind cooling processes.