Radiosonde Wind Research Articles

Cloud motion winds from METEOSAT: performance of an operational system

Wind fields have been estimated from the displacement of clouds in successive METEOSAT infrared (IR: 10.5–12.5 μm) images for more than a decade. The derivation of cloud motion winds (hereafter: CMW) workss fully automatically, man-machine interaction is only performed as the very last step of manual quality control. At present about 3000 wind vectors per day are produced with four production runs and disseminated via the Global Telecommunication System (GTS) mainly for use in the analysis for numerical weather prediction. In this paper the improvements to the CMW derivation from METEOSAT images are described. In particular the height assignment of a wind vector and radiance filtering techniques preceding the cloud tracking have ameliorated the errors in METEOSAT winds significantly. The low speed bias of high level CMWs (< 400 hPa) in comparison with radiosonde winds has been reduced by more than 60% since 1987. This has significantly enhanced the usefulness of CMWs for the global analysis/forecast systems and hence their potential for climate diagnostic studies.

Automated extraction of cloud motion vectors from INSAT-1B imagery

The paper describes an automated technique for cloud motion vector extraction from INSAT -ID on visible and infra-red imagery over the oceanic areas around the Indian Peninsula. The technique is based on a pattern matching procedure which attempts to search for a pixel-to-pixel eqality between two grey shade distributions instead of cross-correlation. The CMVs are found to be very useful m augmenting the wind data over the oceanic areas and are consistent with each other and neighbouring radiosonde winds. The paper also discusses the sources of errors and uncertainties caused by the VHRR resolution and the wind derivation procedure.

Monitoring of Observation and Analysis Quality by a Data Assimilation System

The purpose of this paper is to demonstrate the ability of a modern data assimilation system to provide long-term diagnostic facilities to monitor the performance of the observational network. Operational data assimilation systems use short-range forecasts to provide the background, or first-guess, field for the analysis. We make a detailed study of the apparent or perceived error of these forecasts when they are verified against radiosondes. On the assumption that the observational error of the radiosondes is horizontally uncorrelated, the perceived forecast error can be partitioned into prediction error, which is horizontally correlated, and observation error, which is not. The calculations show that in areas where there is adequate radiosonde coverage, the 6-hour prediction error is comparable with the observation error. This statement is discussed from a number of viewpoints. We demonstrate in the Northern Hemisphere midlatitudes, for example, that the forecasts account for most of the evolution of the atmospheric state from one analysis to the next, so that the analysis algorithm needs to make only a small correction to an accurate first-guess field; the situation is rather different in the Southern Hemisphere. If the doubling time for small errors is two days, then analysis error will amplify by less than 10% in 6 hours. This being the case, the statistics of the forecast/observation differences have a simple statistical structure. Large variations of the statistics from station to station, or large biases, are indicative of problems in the data or in the assimilation system. Case studies demonstrate the ability of simple statistical tools to identify systematically erroneous radiosonde wind data in data sparse, as well as in data rich areas, errors which would have been difficult to detect in any other way. The statistical tools are equally effective in diagnosing the performance of the assimilation system. The results suggest that it is possible to provide regular feedback on the quality of observations of winds and heights to operators of radiosonde networks and other observational systems. This capability has become available over the last decade through improvements in the techniques of numerical weather analysis and prediction.

The Observational Error of Automated Wind Reports from Aircraft

Data collected from aircraft equipped with AIDS (Aircraft Integrated Data System) instrumentation during the Global Weather Experiment year of 1979 are used to estimate the observational error of winds at flight level from this and other aircraft automated wind-reporting systems. Structure functions are computed from reports that are paired using specific criteria. The value of this function extrapolated to zero separation distance is an estimate of twice the random measurement-error variance of the AIDS-measured winds. Component-wind errors computed in this way range from 2.1 to 3.1 m · s−1 for the two months of data examined, January and August 1979. Observational error, specified in optimum-interpolation analyses to allow the analysis to distinguish among observations of differing quality, is composed of both measurement error and the error of unrepresentativeness. The latter type of error is a function of the resolvable scale of the analysis-prediction system. The structure function, which measures the variability of a field as a function of separation distance, includes both of these types of error. If the resolvable scale of an analysis procedure is known, an estimate of the observational error can be computed from the structure function at that particular distance. An observational error of 5.3 m · s−1 was computed for the u and v wind components for a sample resolvable scale of 300 km. The errors computed from the structure functions are compared to colocation statistics from radiosondes. The errors associated with automated wind reports are found to compare favorably with those estimated for radiosonde winds at that level.

Postset beam steering and interferometer applications of VHF radars to study winds, waves, and turbulence in the lower and middle atmosphere

Spaced antenna VHF radar measurements are utilized for the postset beam steering technique and for interferometer applications to study winds, waves, and turbulence in the stratosphere and mesosphere. Following a brief description of the basic instrumental setup and the off‐line analysis method, some results are presented which demonstrate the consistency and applicability of these methods. Vertical velocity oscillations due to gravity waves are analyzed by means of the cross‐spectrum technique. It is shown that phase differences of gravity wave oscillations, measured between vertical and two opposite, off‐vertical postset beams, change their sign when the beam is swung back and forth. The same features of change of velocity sign are noticed when the mean wind is observed. The mean wind deduced with the postset beam steering technique is similar to the wind deduced with the spaced antenna drift technique and the independent radiosonde winds. Taking these results as justification for the applicability and feasibility of the postset beam steering method, the total wave vector and the intrinsic angular frequency of gravity waves in the stratosphere are deduced. Reasonable arguments are discussed to support the suggestion that these waves were generated in lower stratosphere wind shear regions and were attenuated little when propagating up to the middle stratosphere. Turbulence blobs in the mesosphere are tracked with the interferometer technique. It is shown that these blobs moved horizontally as well as vertically, a feature which cannot unequivocally be detected with conventional Doppler methods.

Can a VHF Doppler Radar Provide Synoptic Wind Data? A Comparison of 30 Days of Radar and Radiosonde Data

Abstract A number of experiments have shown that UHF and VHF Doppler radars can make “clear air” wind measurements in the troposphere and lower stratosphere, even in the presence of clouds and precipitation. Past comparisons of radar and rawinsonde profiles for a single day have shown good agreement between the two within the limitations imposed by the spatial separation between the two measurements. However, the accuracy of the measurement does not insure that the data are synoptically significant. A comparison of 30 days of radiosonde geopotential height and wind data and radar data from Alaska was carried out to determine the applicability of the radar data to synoptic meteorology. Rawinsonde and radar wind time series at six heights between 3.79 and 14.79 km altitude were compared and the rms differences calculated. The two independent wind measurements were also compared to the geostrophic wind obtained from the geopotential height fields generated by applying the Cressman objectives analysis scheme ...

Improved Cloud Motion Wind Vector and Altitude Assignment Using VAS

Abstract A CO2 cloud tracking technique to determine simultaneous heights and velocities of cloud motion winds is presented. Using animated CO2 channel imagery from VAS, multi-level cloud situations are separated into high, middle and low level cloud motion wind vectors by the CO2 slicing method. The VAS CO2 channel radiometric values are used in the CO2 absorption method to assign quantitative heights to the cloud vectors; cloud top pressures are determined from the ratio of the deviations in cloud produced radiances and the corresponding clear air values for three CO2 channels in a radiative transfer equation formulation. Two case studies are presented that show CO2 cloud-motion wind vectors to be in good agreement with radiosonde wind observations and CO2 cloud heights to be within a 50 mb rms deviation of radiosonde, bispectral and stereo height determinations.

The Relationship Between Deep Ocean Currents and Winds East of Barbados

Abstract Observations of currents collected at the POLYMODE array III cluster C (16°N, 54°W) are compared with radiosonde winds measured at Barbados (13°N, 62°W) using a linear response analysis. The winds and the currents are coherent throughout the water column (5400 m) over the subinertial frequency range of 0.025 to 0.25 cpd. The coherence is highest between the east-west wind stress and north-south currents over smooth topography. The wind-related ocean currents have a rms of 2.5 cm s−1 at 500 m and 1.1 cm s−1 at 4000 m and account for approximately one-third of the total eddy kinetic energy. The wind-current phase is depth independent and does not vary significantly over the 200 km horizontal scale of the array. The response amplitude is surface intensified and increases with decreasing frequency which is consistent with a deterministic theoretical model. The coherence values and response estimates suggest an off-resonant barotropic response to large-scale wind forcing.

First low-power VHF radar observations of tropospheric, stratospheric and mesospheric winds and turbulence at the Arecibo Observatory

First VHF radar measurements with height resolution of 300 m and angular resolution of 1.7° were carried out in low latitudes at the Arecibo Observatory, Puerto Rico. A short outline is given of the experimental set-up which consisted of a 160W average power radar-transceiver and a self-contained digital radar control and data acquisition unit. The new VHF feed system of the Arecibo dish is described shortly. Reliable radar echoes were detected from the troposphere, lower stratosphere and from some heights in the mesosphere, indicating that the described VHF radar is capable of proper investigations of dynamical processes in the low latitude middle atmosphere. The angular dependence of aspect sensitive tropospheric and stratospheric turbulence structures was measured to be 1.5–2.5 dB degree −1. Echoes from the mesosphere indicate a patchy structure of turbulence. The analysis of the signal-to-noise ratio shows considerably high reflectivity in the upper troposphere, which can be caused by high-reaching tropical cumulus convection. Wind profiles measured with the VHF radar between 7.5 and 19.5 km with a height resolution of 300m are very similar to radiosonde wind profiles. Mesospheric VHF radar winds are roughly consistent in amplitude with tidal winds.

Determination of wind vectors from METEOSAT water vapor channel data

After applying special edge detection techniques to METEOSAT water vapor images midtropospheric wind vectors have been derived in cloudfree areas by using the single point tracking method. A comparison of derived wind vectors with radiosonde winds gave rms-differences of 5ms −1 for wind velocity and 16° for wind direction.

On Upper Tropospheric Kinematics and Severe Weather Occurrence

Abstract Upper tropospheric wind maxima and their associated divergence fields are examined in terms of severe weather occurrence. A two-part project is described. Part I involves examination of severe weather occurrences and divergence areas qualitatively evaluated in terms of upper tropospheric wind maxima quadrants and the curvature of the flow. Part II calculates synoptic-scale divergence directly from radiosonde wind data. These quantitative divergence estimates are compared with the location of upper tropospheric wind maxima, wave troughs and severe weather occurrence. It is concluded that regions of upper tropospheric divergence are present with the occurrence of severe weather and, in particular, with the occurrence of severe weather outbreaks. Several examples are presented to support the ideas discussed.

A Comparison of Cloud Motion Winds with Coinciding Radiosonde Winds

The relative capability of a wind derived from tracking the movement of clouds displayed in SMS-I infrared image sequence and of a wind reported by a radiosonde to represent atmospheric motion was investigated. Cloud winds intercompared with radiosonde winds over North America gave mean absolute differences between a cloud wind and surrounding radiosonde winds of 4.4 m s−1 for the u component and 4.6 m s−1 for the v component. An intracomparison of radiosonde winds for the same periods gave mean absolute differences between a radiosonde wind and surrounding reports of 4.2 m s−1 for the u component and 5.1 in s−1 for the v component. These and associated results suggest that a cloud wind and a radiosonde wind have a similar capability to represent atmospheric motions.

On the Estimation of Kinematic Parameters in the Atmosphere From Radiosonde Wind Data

Abstract A technique is proposed for computing horizontal velocity divergence and the vertical component of vorticity from radiosonde wind data. Utilizing a quadratic Taylor's series representation of the horizontal wind field, one can consider nonlinear variations in the wind directly in estimates of the first-order derivatives of the wind components. These nonlinear variations are found to be significant in a number of cases. Vertical motions computed by the kinematic method and horizontal divergence are modified by an adjustment scheme. Comparison of these results with those derived from computations from a linear Taylor's series representation of the wind suggests that the quadratic model is superior to the linear. Synoptic analyses of vorticity, divergence, and vertical motions over the United States at 0000 and 1200 GMT on Apr. 13, 1964, reveal good agreement with the circulation patterns and associated weather.

AN ANALYSIS OF KINEMATIC VERTICAL MOTIONS

Abstract Several techniques exist for computing vertical motions. In this paper, radiosonde wind observations are used to compute vertical motions by the kinematic method. The presence of cumulative bias errors necessitates adjustment techniques. Simple tests of two techniques indicate that, for the period of this study, a divergence adjustment that is a function of pressure yields the best adjusted vertical motion fields. Further analysis shows that the adjusted estimates correlate well with observed synoptic features. Finally, comparison with estimates by the numerical method indicates that adjusted kinematic vertical motion fields are comparable.

Magnitude of terms in the equation for large-scale atmospheric motions

The magnitude of the terms in the equation of motion as applied to motions in the upper troposphere at weather-map scale have been investigated by objective statistical procedures. The appropriate large-scale variance of the radiosonde winds has been extracted from the original record by employing the variance spectrum of isobaric height as a guide to the large-scale structure. The objective analysis shows that the departure of the radiosonde wind from the geostrophic wind is larger in the direction of the flow than transverse to the flow, and the ratio of the standard deviation of the geostrophic departure to the mean wind speed has the same magnitude at 500 and 300 mb. The longitudinal and transverse component ratios have the value 0.25 and 0.15, respectively. Under the most favorable circumstance about half the variance of the observed geostrophic departures must either be due to error or be associated with small-scale motions. The remaining variance of the geostrophic departure at large scale provides an estimate of the large-scale accelerations, which has been confirmed by a correlation of the geostrophic departures with the acceleration of the geostrophic wind. The frictional force has been estimated from the systematics of the geostrophic departures, which suggest that the frictional force, at least in the direction transverse to the flow, approaches a value comparable to the large-scale geostrophic departure. The comparison of geostrophic and radiosonde winds also shows that the poleward transport of momentum in central United States is largely accomplished by the ageostrophic component of the wind.

Mid-latitude atmospheres, winter and summer

Winter and summer Mid-Latitude (45oN) atmospheres to 90 km, two of a family of nine atmospheres supplemental to the U.S. Standard Atmosphere (1962), provide information on atmospheric structure by seasons rather than the mean annual data shown in the Standard, which is described for reference. Principal data sources for constructing these atmospheres consisted of summaries of Northern Hemisphere radiosonde observations at stations near, 45oN, and observations made from rockets and instruments released by rockets, from nearly a dozen Northern Hemisphere launching sites. Winter and summer temperature-height profiles begin with surface temperatures of −1° and +21 °C, respectively, and contain three isothermal layers: −58°C at 19 to 27 km in winter and −57.5°C at 13 to 17 km in summer; −7.5° and +2.5°C at 47 to 52 km; and −79.5 and −99°C at 80 to 90 km, respectively. The temperature-height curve for the U.S. Standard has a surface temperature of +15°C with isothermal regions at 11 to 20 km (−56.5°C), 47 to 52 km (−2.5°C), and 80 to 90 km (−92.5°C). In all three atmospheres, temperature gradients for various segments are linear with geopotential, height. Humidity is incorporated into the lowest 10 km of the Supplemental Atmospheres, whereas the Standard is dry. Figures and tables depict temperature, relative humidity, pressure, and density for winter and summer, and temperature, pressure, density, speed of sound, and dynamic viscosity for the U.S. Standard Atmosphere. The Supplemental Atmospheres are mutually consistent; zonal wind profiles, computed from the geostrophic wind equation and selected pressure heights, compare favorably with existing radiosonde and rocket wind observations.

Mountain waves over Banks Peninsula, New Zealand

Summary Twenty-seven occurrences of wave motion in the atmosphere over the hilly terrain of Banks Peninsula, South Island, New Zealand, have been analysed from the Christchurch radiosonde and radar wind records. The average maximum vertical velocity found was approximately 1,000 ft per min., but velocities up to 2,000 ft per min. were found to occur occasionally. The conditions in which these waves may exist and some of their characteristic properties are given.