Simultaneous Wind Measurements Research Articles

Vientos—A New Satellite Mission Concept for 3D Wind Measurements by Combining Passive Water Vapor Sounders with Doppler Wind Lidar

Abstract It is challenging to accurately characterize the three-dimensional distribution of horizontal wind vectors (known as 3D winds). Feature-matching satellite cloud top or water vapor fields have been used for decades to retrieve atmospheric motion vectors, but this approach is mostly limited to a single and uncertain pressure level at a given time. Satellite wind lidar measurements are expected to provide more accurate data and capture the line-of-sight wind for clear skies, within cirrus clouds, and above thick clouds, but only along a curtain parallel to the satellite track. Here we propose Vientos—a new satellite mission concept that combines two or more passive water vapor sounders with Doppler wind lidar to measure 3D winds. The need for 3D wind observations is highlighted by inconsistencies in reanalysis estimates, particularly under precipitating conditions. Recent studies have shown that 3D winds can be retrieved using water vapor observations from two polar-orbiting satellites separated by 50 min, with the help of advanced optical flow algorithms. These winds can be improved through the incorporation of a small number of collocated higher-accuracy measurements via machine learning. The Vientos concept would enable simultaneous measurements of 3D winds, temperature, and humidity, and is expected to have a significant impact on scientific research, weather prediction, and other applications. For example, it can help better understand and predict the preconditions for organized convection. This article summarizes recent results, presents the Vientos mission architecture, and discusses implementation scenarios for a 3D wind mission under current budget constraints.

Spatially distributed and simultaneous wind measurements with a fleet of small quadrotor UAS

The understanding of micro-scale flow in the atmospheric boundary layer is one major challenge in wind energy research. Besides the broad possibilities of numerical simulations, experimental data are necessary for tests of the flow conditions within a wind farm under real conditions. In wind energy and atmospheric science, a variety of measurement devices exist for measuring the wind speed. We propose a measurement system that enables completely flexible simultaneous wind measurements using a fleet of multirotor unmanned aircraft systems (UAS). This approach is validated through a two-week measurement campaign at the boundary layer field site Falkenberg of the German National Meteorological Service (DWD). The wind speed is calculated from UAS motions in hover state without additional wind sensors. The measurements are calibrated and validated against sonic anemometers mounted at a 99 m mast. The capability of highly accurate spatial distributed wind measurement with an improved wind algorithm is proven by a root mean square error (RMSE) of 0.25 ms−1 for the horizontal wind speed and < 5° for the wind direction. Further, turbulence measurements are presented showing valid results up to a frequency of 2 Hz in high turbulence conditions. Additionally, spatially horizontal distributed measurements with multiple UAS are examined in a case study of a gust front event.

Inter-comparison of wind measurements in the atmospheric boundary layer and the lower troposphere with Aeolus and a ground-based coherent Doppler lidar network over China

Abstract. After the successful launch of Aeolus, which is the first spaceborne wind lidar developed by the European Space Agency (ESA), on 22 August 2018, we deployed several ground-based coherent Doppler wind lidars (CDLs) to verify the wind observations from Aeolus. By the simultaneous wind measurements with CDLs at 17 stations over China, the Rayleigh-clear and Mie-cloudy horizontal-line-of-sight (HLOS) wind velocities from Aeolus in the atmospheric boundary layer and the lower troposphere are compared with those from CDLs. To ensure the quality of the measurement data from CDLs and Aeolus, strict quality controls are applied in this study. Overall, 52 simultaneous Mie-cloudy comparison pairs and 387 Rayleigh-clear comparison pairs from this campaign are acquired. All of the Aeolus-produced Level 2B (L2B) Mie-cloudy HLOS wind and Rayleigh-clear HLOS wind and CDL-produced HLOS wind are compared individually. For the inter-comparison result of Mie-cloudy HLOS wind and CDL-produced HLOS wind, the correlation coefficient, the standard deviation, the scaled mean absolute deviation (MAD) and the bias are 0.83, 3.15 m s−1, 2.64 m s−1 and −0.25 m s−1, respectively, while the y=ax slope, the y=ax+b slope and the y=ax+b intercept are 0.93, 0.92 and −0.33 m s−1. For the Rayleigh-clear HLOS wind, the correlation coefficient, the standard deviation, the scaled MAD and the bias are 0.62, 7.07 m s−1, 5.77 m s−1 and −1.15 m s−1, respectively, while the y=ax slope, the y=ax+b slope and the y=ax+b intercept are 1.00, 0.96 and −1.2 m s−1. It is found that the standard deviation, the scaled MAD and the bias on ascending tracks are lower than those on descending tracks. Moreover, to evaluate the accuracy of Aeolus HLOS wind measurements under different product baselines, the Aeolus L2B Mie-cloudy HLOS wind data and L2B Rayleigh-clear HLOS wind data under Baselines 07 and 08, Baselines 09 and 10, and Baseline 11 are compared against the CDL-retrieved HLOS wind data separately. From the comparison results, marked misfits between the wind data from Aeolus Baselines 07 and 08 and wind data from CDLs in the atmospheric boundary layer and the lower troposphere are found. With the continuous calibration and validation and product processor updates, the performances of Aeolus wind measurements under Baselines 09 and 10 and Baseline 11 are improved significantly. Considering the influence of turbulence and convection in the atmospheric boundary layers and the lower troposphere, higher values for the vertical velocity are common in this region. Hence, as a special note, the vertical velocity could impact the HLOS wind velocity retrieval from Aeolus.

Quad-Fabry-Perot etalon based Rayleigh Doppler lidar for 0.2-60km altitude wind, temperature and aerosol accurate measurement

Rayleigh Doppler lidar based on a quad Fabry-Perot etalon (FPE) is proposed that is capable of accurately detecting wind speed, as well as temperature and aerosol from 0.2 to 60km altitude. The structure of lidar is designed and its measurement principle is analyzed. One of the four FPEs, i.e. FPE-L is used for locking and measuring the outgoing laser frequency, and the other three, i.e. FPE-1, -2 and -3 form a three-stage FPE. The first-stage FPE (FPE-1) can effectively filter out Mie backscattering signal, thereby suppressing its effects on wind measurement and measuring the aerosol backscatter ratio as well. The transmission spectra of the second- and third-stage FPEs (FPE-2,-3) form double edge for simultaneous wind and temperature measurements by using Rayleigh backscattering signal. The parameters of the quad FPE are optimized. The FWHM and relative peak position of FPE-1,-2,-3,-L are 0.6, 1.2, 1.2, 0.6GHz and 0, -1, 1, 0.3GHz, respectively. The performance of the proposed lidar is simulated and results show that for 0.3WSr−1m-2nm−1@355nm sky brightness, by using a 350mJ pulse energy, 50Hz repetition frequency laser and a 0.8m aperture telescope, with temporal resolution of 2min@0.2∼20km, 20min@20∼60km and vertical resolution of 45m@0.2∼10km, 90m@10∼ 20km, 180m@20∼40km, 1km@40∼60km, the measurement errors of temperature, aerosol backscattering ratio and vertical wind speed are below 5.3K, 3.0×10-3, 1.1m/s in nighttime and below 14.6K, 8.1×10-3, 2.5m/s in daytime from 0.2 to 60km altitude; the measurement error of two other orthogonal LOS wind speed with fixed zenith angle of 25.8° is below 1.3m/s in nighttime and 3.5m/s in daytime within the LOS wind speed dynamic range of ±50m/s from 0.2 to 60km altitude.

A framework to compare wind loads on low-rise buildings in tornadoes and atmospheric boundary layers

This paper presents a framework to compare the building aerodynamics measured in a tornado-like vortex simulator and a typical boundary layer wind tunnel. The method relies on the hypothesis that the aerodynamic and static pressures can be separated and on simultaneous wind and pressure measurements. Test data from a tornado-vortex simulator and a boundary layer wind tunnel are presented to illustrate the method. The simulated tornado had a swirl ratio such that the core had multiple vortices. A building model was placed to the side of the translation path, at a position 0.8 core radius diameters from the tornado center. Surface pressures were measured on both a circular ground plate and the building model surfaces, synchronized with the velocities measured at four cobra probes placed near each corner of the building. A large set of nominally identical runs were used to obtain ensemble statistics of both pressures and velocities. The static pressure induced by the tornado was removed from the overall building pressures using a conditional average of the ground plane tornado pressure field. A quasi-steady (QS) vector model was developed in boundary layer results for the same building and then used to compare the aerodynamic results in the tornado, based on the velocities measured by the probes near the building in the tornado wind field. The QS model is found to predict the order of pressure variations but misses the local pressure distributions. The estimations are greatly improved when the upstream wind azimuth angles are shifted in the QS model to the direction of tornado rotation. The degree of the required azimuth shift for better predictions are shown to be governed by the curvature of the tornado wind field in the horizontal plane near the building. Furthermore, this curvature of the tornado wind field is observed to reduce the size of separation bubbles on the leeward walls, increasing the magnitude of suctions on these walls. The rotating multi-cell vortices confined in the tornado core also produce high pressure fluctuations that are not well captured by the QS model.

Small-scale structures in noctilucent clouds observed by lidar

Noctilucent clouds (NLC) are mesospheric ice clouds occurring in the summer hemisphere at high latitudes and an altitude of about 83km. This region is the coldest of the earth’s atmosphere and is characterized by the presence of wave interaction and dissipation. The processes involved here lead to a variety of structures and instabilities that become visible in noctilucent clouds and are observed by different instruments. In this work high-resolution lidar measurements are used to give a wide overview of the structures at small scales below the Brunt–Väisälä period of ∼5min. For the first time a large amount of NLC profiles from lidar with a temporal resolution of 1s is analyzed in detail, covering about 1400h during the summer from 2011 to 2018. A new categorization focusing on small-scale structures is introduced, and occurrence statistics for these categories in the season of 2014 are performed. Both wave structures with periods below 10min and thin layers of <100m thickness are commonly found. When taking simultaneous wind measurements into account, we find that structures often are advected by the wind.

Measuring Winds and Currents with Ka-Band Doppler Scatterometry: An Airborne Implementation and Progress towards a Spaceborne Mission

Ocean surface winds and currents are tightly coupled, essential climate variables, synoptic measurements of which require a remote sensing approach. Global measurements of ocean vector winds have been provided by scatterometers for decades, but a synoptic approach to measuring total vector surface currents has remained elusive. Doppler scatterometry is a coherent burst-scatterometry technique that builds on the long heritage of spinning pencil beam scatterometers to enable the wide-swath, simultaneous measurement of ocean surface vector winds and currents. To prove the measurement concept, NASA funded the DopplerScatt airborne Doppler scatterometer through the Instrument Incubator Program (IIP) and Airborne Instrument Technology Transition (AITT) program. DopplerScatt has successfully shown that pencil beam Doppler scatterometry can be used to form wide swath measurements of ocean winds and currents, and has increased the technology readiness level of key instrument components, including: Ka-band pulsed radar hardware, optimized scatterometer burst-mode operation, calibration techniques, geophysical model functions, and processing algorithms. With the promise and progress shown by DopplerScatt, and the importance of air-sea interactions in mind, the National Academy’s Decadal Survey has targeted simultaneous measurements of winds and currents from a Doppler scatterometer for an Earth Explorer class spaceborne mission. Besides DopplerScatt’s place as a technology stepping stone towards a satellite mission, DopplerScatt provides scientifically important measurements of ocean currents and winds (400 m resolution) and their derivatives (1 km resolution) over a 25 km swath. These measurements are enabling studies of the submesoscales and air-sea interactions that were previously impossible, and are central to the upcoming NASA Earth Ventures Suborbital-3 Submesoscale Ocean Dynamics Experiment (S-MODE). This paper summarizes the development of DopplerScatt hardware, systems, calibration, and operations, and how advances in each relate to progress towards a spaceborne Doppler scatterometer mission.

Response of Sporadic E Layer to Sudden Stratospheric Warming Events Observed at Low and Middle Latitudes

AbstractThis paper investigates the variations of middle‐ and low‐latitude sporadic E (Es) layers during 2011–2012 and 2012–2013 sudden stratospheric warming (SSW) events by using observations from six ionosondes in East Asia over China and Japan region. Observations of Es critical frequency (foEs) at all these ionosondes present obvious enhancements around the days of new and full moon during SSW periods. Wavelet spectra of foEs during two SSW events exhibit noticeable enhanced 14.5‐day modulation, which resembles the lunar semimonthly period. In addition, simultaneous wind measurements by meteor radar also show enhancement of 14.5‐day periodic oscillation after SSW onset. Tidal components extracted from meteor radar wind measurements in mesosphere and lower thermosphere region and from ionospheric F region critical frequency (foF2) are noticeably modulated by the lunar phase. These observational evidences reveal that the semimonthly lunar period of 14.5 days can be a contributing factor to variations of Es layer during SSW event.

The Winds and Currents Mission Concept

The Winds and Currents Mission (WaCM) is a proposed approach to meet the need identified by the NRC Decadal Survey for the simultaneous measurements of ocean vector winds and currents. WaCM features a Ka-band pencil-beam Doppler scatterometer able to map ocean winds and currents globally. We review the principles behind the WaCM measurement and the requirements driving the mission. We then present an overview of the WaCM observatory and tie its capabilities to other OceanObs reviews and measurement approaches.

The possibility of using all-sky meteor radar to observe ionospheric E-region field-aligned irregularities

All-sky meteor radars are primarily used for meteor observations. This paper reports the first observations of ionospheric E-region field-aligned irregularities (FAIs) from a conventional all-sky meteor radar located at Wuhan (31°N, 114°E) for the period of March–June 2018. E-region FAI echoes evident in range-time intensity (RTI) maps show quasiperiodic striations with positive and negative slopes, which are consistent with multiple FAI structures moving across the wide beam of the meteor radar. A statistical analysis shows that out of a total of 111 d, there are 73 d with E-region FAI echoes detected by the meteor radar. The FAI events correspond well with the presence of sporadic-E layers which provide the necessary plasma density gradient for the development of gradient drift instability producing FAIs. The results demonstrate the capability of conventional meteor radars to make simultaneous routine observations of meteors and ionospheric E-region FAIs through incorporating RTI and spectral analysis into the online realtime data processing. Meteor radar observations could potentially address the limitations of ionospheric radars, which cannot provide simultaneous measurements of neutral winds and irregularity structures, and thereby contribute to better understanding of the dynamical processes producing E-region irregularities.

On the Long Lasting “C‐Type” Structures in the Sodium Lidargram: The Lifetime of Kelvin‐Helmholtz Billows in the Mesosphere and Lower Thermosphere Region

AbstractIn order to understand the characteristics of long‐lasting “C‐type” structure in the Sodium (Na) lidargram, six cases from different observational locations have been analyzed. The Na lidargram, collected from low‐, middle‐, and high‐latitude sites, show long lifetime of the C‐type structures which is believed to be the manifestation of Kelvin‐Helmholtz (KH) billows in the Mesosphere and Lower Thermosphere (MLT) region. In order to explore the characteristics of the long‐lasting C‐type structures, the altitude profile of square of Brunt‐Väisälä frequency in the MLT region has been derived using the temperature profile collected from the Na lidar instruments and the SABER instrument onboard TIMED satellite. It is found to be positive in the C‐type structure region for all the six cases which indicates that the regions are convectively stable. Simultaneous wind measurements, which allowed us to calculate the Richardson numbers and Reynolds numbers for three cases, suggest that the regions where the C‐type structure appeared were dynamically stable and nonturbulent. This paper brings out a hypothesis wherein the low temperature can increase the magnitude of the Prandtl number and convectively stable atmospheric region can cause the magnitude of Reynolds number to decrease. As a consequence, the remnant of previously generated KH billows in nearly “frozen‐in” condition can be advected through this conducive region to a different location by the background wind where they can sustain for a long time without much deformation. These long‐lived KH billows in the MLT region will eventually manifest the long‐lasting C‐type structures in the Na lidargram.

On the short-term variability of turbulence and temperature in the winter mesosphere

Abstract. Four mesosphere–lower thermosphere temperature and turbulence profiles were obtained in situ within ∼30 min and over an area of about 100 by 100 km during a sounding rocket experiment conducted on 26 January 2015 at Poker Flat Research Range in Alaska. In this paper we examine the spatial and temporal variability of mesospheric turbulence in relationship to the static stability of the background atmosphere. Using active payload attitude control, neutral density fluctuations, a tracer for turbulence, were observed with very little interference from the payload spin motion, and with high precision (&lt;0.01 %) at sub-meter resolution. The large-scale vertical temperature structure was very consistent between the four soundings. The mesosphere was almost isothermal, which means more stratified, between 60 and 80 km, and again between 88 and 95 km. The stratified regions adjoined quasi-adiabatic regions assumed to be well mixed. Additional evidence of vertical transport and convective activity comes from sodium densities and trimethyl aluminum trail development, respectively, which were both observed simultaneously with the in situ measurements. We found considerable kilometer-scale temperature variability with amplitudes of 20 K in the stratified region below 80 km. Several thin turbulent layers were embedded in this region, differing in width and altitude for each profile. Energy dissipation rates varied between 0.1 and 10 mW kg−1, which is typical for the winter mesosphere. Very little turbulence was observed above 82 km, consistent with very weak small-scale gravity wave activity in the upper mesosphere during the launch night. On the other hand, above the cold and prominent mesopause at 102 km, large temperature excursions of +40 to +70 K were observed. Simultaneous wind measurements revealed extreme wind shears near 108 km, and combined with the observed temperature gradient, isolated regions of unstable Richardson numbers (0&lt;Ri&lt;0.25) were detected in the lower thermosphere. The experiment was launched into a bright auroral arc under moderately disturbed conditions (Kp∼5).

Estimating Maximum Significant Wave Height and Dominant Wave Period inside Tropical Cyclones

Abstract Making use of the fetch- and duration-limited nature of wind-wave growth inside tropical cyclones, an algorithm is developed to estimate the maximum significant wave height and dominant wave period of surface waves generated by tropical cyclone wind fields. The results of the maximum significant wave height and dominant wave period are further approximated by simple power functions of the maximum wind speed. The exponents of the power functions are almost constant, and the proportionality coefficients can be approximated by second-order polynomial functions of the radius of maximum wind speed (RMW). The predicted maximum values agree well with results derived from simultaneous wind and wave measurements obtained during 11 hurricane reconnaissance and research missions in six hurricanes.

Estimating Ocean Vector Winds and Currents Using a Ka-Band Pencil-Beam Doppler Scatterometer

Ocean surface currents and winds are tightly coupled essential climate variables, and, given their short time scales, observing them at the same time and resolution is of great interest. DopplerScatt is an airborne Ka-band scatterometer that has been developed under NASA’s Instrument Incubator Program (IIP) to provide a proof of concept of the feasability of measuring these variables using pencil-beam scanning Doppler scatterometry. In the first half of this paper, we present the Doppler scatterometer measurement and processing principles, paying particular attention to deriving a complete measurement error budget. Although Doppler radars have been used for the estimation of surface currents, pencil-beam Doppler Scatterometry offers challenges and opportunities that require separate treatment. The calibration of the Doppler measurement to remove platform and instrument biases has been a traditional challenge for Doppler systems, and we introduce several new techniques to mitigate these errors when conical scanning is used. The use of Ka-band for airborne Doppler scatterometry measurements is also new, and, in the second half of the paper, we examine the phenomenology of the mapping from radar cross section and radial velocity measurements to winds and surface currents. To this end, we present new Ka-band Geophysical Model Functions (GMFs) for winds and surface currents obtained from multiple airborne campaigns. We find that the wind Ka-band GMF exhibits similar dependence on wind speed as that for Ku-band scatterometers, such as QuikSCAT, albeit with much greater upwind-crosswind modulation. The surface current GMF at Ka-band is significantly different from that at C-band, and, above 4.5 m/s has a weak dependence on wind speed, although still dependent on wind direction. We examine the effects of Bragg-wave modulation by long waves through a Modululation Transfer Function (MTF), and show that the observed surface current dependence on winds is consistent with past Ka-band MTF observations. Finally, we provide a preliminary validation of our geophysical retrievals, which will be expanded in subsequent publications. Our results indicate that Ka-band Doppler scatterometry could be a feasible method for wide-swath simultaneous measurements of winds and currents from space.

Peak height of OH airglow derived from simultaneous observations a Fabry‐Perot interferometer and a meteor radar

AbstractA new method for estimating daily averaged peak height of the OH airglow layer from a ground‐based meteor radar (MR) and a Fabry‐Perot interferometer (FPI) is presented. The first results are derived from 4 year simultaneous measurements of winds by a MR and a FPI at two adjacent stations over center China and are compared with observations from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument. The OH airglow peak heights, which are derived by using correlation analysis between winds of the FPI and MR, are found to generally peak at an altitude of 87 km and frequently varied between 80 km and 90 km day to day. In comparison with SABER OH 1.6 μm observations, reasonable similarity of airglow peak heights is found, and rapid day‐to‐day variations are also pronounced. Lomb‐Scargle analysis is used to determine cycles of temporal variations of airglow peak heights, and there are obvious periodic variations both in our airglow peak heights and in the satellite observations. In addition to the annual, semiannual, monthly, and three monthly variations, the shorter time variations, e.g., day‐to‐day and several days' variations, are also conspicuous. The day‐to‐day variations of airglow height obviously could reduce observation accuracy and lead to some deviations in FPI measurements. These FPI wind deviations arising from airglow height variations are also estimated to be about 3–5 m/s from 2011 to 2015, with strong positive correlation with airglow peak height variation. More attention should be paid to the wind deviations associated with airglow height variation when using and interpreting winds measured by FPI.

Effective Fetch and Duration of Tropical Cyclone Wind Fields Estimated from Simultaneous Wind and Wave Measurements: Surface Wave and Air–Sea Exchange Computation

AbstractSimultaneous wind and wave measurements have been obtained inside tropical cyclones in several hurricane hunter missions. Analyses of these datasets show that the surface wave development inside hurricanes follows essentially the same duration- and fetch-limited growth functions established in steady wind forcing conditions. This paper explores the application of several parameterization functions of wind-wave systems to quantify the energy and momentum exchanges inside hurricanes from an initially limited input of the environmental parameters, such as the wind field alone. A critical prerequisite to applying the wind-wave growth functions is the knowledge of fetch and duration for the hurricane wind field. Four sets of simultaneous wind and wave measurements from hurricane hunter missions are analyzed to derive a fetch and duration scaling model. Time series of 2D hurricane wind fields can then be used to investigate the detailed spatial distribution and temporal evolution of the sea state parameters and the associated air–sea energy and momentum exchanges following the hurricane development.

Saharan dust long-range transport across the Atlantic studied by an airborne Doppler wind lidar and the MACC model

Abstract. A huge amount of dust is transported every year from north Africa into the Caribbean region. This paper presents an investigation of this long-range transport process based on airborne Doppler wind lidar (DWL) measurements conducted during the SALTRACE campaign (June–July 2013), as well as an evaluation of the ability of the MACC (Monitoring Atmospheric Composition and Climate) global aerosol model to reproduce it and its associated features. Although both the modeled winds from MACC and the measurements from the DWL show a generally good agreement, some differences, particularly in the African easterly jet (AEJ) intensity, were noted. The observed differences between modeled and measured wind jet speeds are between 5 and 10 m s−1. The vertical aerosol distribution within the Saharan dust plume and the marine boundary layer is investigated during the June–July 2013 period based on the MACC aerosol model results and the CALIOP satellite lidar measurements. While the modeled Saharan dust plume extent shows a good agreement with the measurements, a systematic underestimation of the marine boundary layer extinction is observed. Additionally, three selected case studies covering different aspects of the Saharan dust long-range transport along the west African coast, over the North Atlantic Ocean and the Caribbean are presented. For the first time, DWL measurements are used to investigate the Saharan dust long-range transport. Simultaneous wind and backscatter measurements from the DWL are used, in combination with the MACC model, to analyze different features associated with the long-range transport, including an African easterly wave trough, the AEJ and the intertropical convergence zone.

Gravity waves observation of wind field in stratosphere based on a Rayleigh Doppler lidar.

Simultaneous wind and temperature measurements in stratosphere with high time-spatial resolution for gravity waves study are scarce. In this paper we perform wind field gravity waves cases in the stratosphere observed by a mobile Rayleigh Doppler lidar. This lidar system with both wind and temperature measurements were implemented for atmosphere gravity waves research in the altitude region 15-60 km. Observations were carried out for two periods of time: 3 months started from November 4, 2014 in Xinzhou, China (38.425°N,112.729°E) and 2 months started from October 7, 2015 in Jiuquan, China (39.741°N, 98.495°E) . The mesoscale fluctuations of the horizontal wind velocity and the two dimensional spectra analysis of these fluctuations show the presence of dominant oscillatory modes with wavelength of 4-14 km and period of around 10 hours in several cases. The simultaneous temperature observations make it possible to identify gravity wave cases from the relationships between different variables: temperature and horizontal wind. The observed cases demonstrate the Rayleigh Doppler Lidar's capacity to study gravity waves.

DopSCAT: A mission concept for simultaneous measurements of marine winds and surface currents

AbstractA radar scatterometer operates by transmitting a pulse of microwave energy toward the ocean's surface and measuring the normalized (per‐unit‐surface) radar backscatter coefficient (σ°). The primary application of scatterometry is the measurement of near‐surface ocean winds. By combining σ° measurements from different azimuth angles, the 10 m vector wind can be determined through a Geophysical Model Function (GMF), which relates wind and backscatter. This paper proposes a mission concept for the measurement of both oceanic winds and surface currents, which makes full use of earlier C‐band radar remote sensing experience. For the determination of ocean currents, in particular, the novel idea of using two chirps of opposite slope is introduced. The fundamental processing steps required to retrieve surface currents are given together with their associated accuracies. A detailed description of the mission proposal and comparisons between real and retrieved surface currents are presented. The proposed ocean Doppler scatterometer can be used to generate global surface ocean current maps with accuracies better than 0.2 m/s at a spatial resolution better than 25 km (i.e., 12.5 km spatial sampling) on a daily basis. These maps will allow gaining some insights on the upper ocean mesoscale dynamics. The work lies at a frontier, given that the present inability to measure ocean currents from space in a consistent and synoptic manner represents one of the greatest weaknesses in ocean remote sensing.

On the internal boundary layer related wind stress curl and its role in generating shallow lake circulations

Abstract The paper demonstrates that the wind stress curl as an external vorticity source plays an important role in shaping large scale shallow lake circulations. The analysis of purpose-oriented simultaneous wind and current measurements data from the Hungarian part of Lake Neusiedl reasonably fits well the internal boundary layer development theory over the lake surface. A 2-D vorticity formulation of wind-induced flows is used to demonstrate mathematically the IBL-related large scale circulation generation mechanism well reflected in the measured data. Further validation of the findings is carried out by means of simple 2-D numerical flow modelling, in which details on the flow pattern besides the measurement sites could be also revealed. Wind-induced lake circulations linked to IBL development shows a novelty to be implemented in up-to-date numerical flow models.