Level II-b Data Research Articles

Complex Quality Control of Meteorological Observations

A survey of the so-called complex quality control (CQC) of meteorological information is presented. The principles of the CQC approach are formulated. The CQC of rawinsonde height and temperature data at mandatory isobaric surfaces is described in detail. This CQC has been implemented into routine practice at the Hydro-meteorological Center in Moscow. It has been also applied at the World Data Center in Obninsk for the quality control of the FGGE Level IIb data. Some results of the CQC operations are presented. Possibilities and ways to apply the CQC approach to other kinds of meteorological information are also discussed.

Onset of the Asian Summer Monsoon in 1979 and the Effect of the Tibetan Plateau

Abstract The time evolution of the general circulation over Asia during an 80-day period from mid-April to early July 1979 is studied using objectively analyzed FGGE Level II-b data. Through the analyses of the wind, temperature, precipitation, outgoing longwave radiation (OLR) flux, and heat and moisture budgets in the area 0°–50°N, 40°–130°E, the major changes of the circulation leading to the onset of the summer monsoon and the role of the Tibetan Plateau in these changes are examined. During the analyzed period the general circulation underwent two distinct stages of abrupt transitions resulting in the successive onsets of early summer rains over Southeast Asia and the Indian summer monsoon. The first transition occurred in May in which low-level southwesterlies began over the longitudes east of 80°E (from the Bay of Bengal to the South China Sea), resulting in the spreading of early summer rains over Assam, the Bay of Bengal coasts of Burma and the Malay Peninsula, Thailand, Indochina and the South C...

Four-Dimensional Data Assimilation in the Monsoon Region. Part I: Experiments with Wind Data

A limited primitive equation model has been used to study the feasibility of four-dimensional data assimilation in the monsoon region and, further, to study the applicability of several assimilation techniques currently being employed in global models. The two fundamental objectives of this research are (i) to understand how the model atmosphere responds to the insertion of asynchronous data and its impact on the assimilation-prediction cycle, and (ii) to determine what assimilation strategies work best for limited-area models in the tropics. A sequence of ten assimilation experiments are performed using different update procedures; all insertions are carried out with only the wind observations. The model is initialized with the ECMWF FGGE level III-b data for the onset vortex case of 17 June 1979, and assimilations are carried out using the summer MONEX level II-b data during the first 12 hours. From these assimilated states, 24-h forecasts are then made. The results lend support to the premise that the required initial conditions can be obtained by the process of four-dimensional updating of the prognostic variables. The results also clearly demonstrate the superiority of the continuous assimilation approach via Newtonian nudging over that by indirect insertion. Furthermore, the insertion shocks are significantly minimized by assimilating only the rotational component of the winds. On the other hand, the application of noise control measures only marginally alleviate the insertion shocks accompanying continuous indirect insertion.

Data assimilation: The 1984/85 revisions of the ECMWF mass and wind analysis

A comprehensive evaluation of the ECMWF operational data assimilation system has been made, based largely on statistics of its performance over a long period of time. the evaluation has identified many deficiencies, covering such aspects of the analysis as the optimum interpolation statistics, the data selection algorithms, and the quality control criteria applied within the analysis. The observation and forecast error variances were seriously in error in the stratosphere and in the tropics. A more faithful model of the forecast error spectrum is provided by the Bessel function expansion than by the Gaussian model. the vertical structure of the height error is assumed to be composed of two components: a ‘barotropic’ part related to a horizontally constant mode and a ‘baroclinic’ structure for the horizontally varying modes. the wind field errors also have a large-scale component. the extratropical vertical correlation remained similar to the earlier correlations, but the tropical height and wind structures changed dramatically. Reasonable rejection limits were defined from the distributions of the observation departures from the first guess, as were observation errors for satellite and aircraft wind reports and Australian pseudo-observations. A comprehensive and homogeneous data selection algorithm has been devised. However, it has been found necessary to exclude land surface wind reports from the analysis process as the wind departures from a first-guess field commonly contradict the surface pressure departures due to difficulties in generating a reasonable 10 m first-guess wind. the omission of surface winds alleviated the data selection problem in data-dense regions. The representation of the vertical correlations was changed to a continuous representation in the vertical which enabled a multivariate interpolation from data on standard pressure levels directly to model coordinates. the earlier procedure used a multivariate interpolation to constant pressure surfaces in the model grid, followed by a univariate interpolation to model surfaces in the vertical. The results of these improvements, in a series of tests covering in total some 30 days of assimilations, are also described. In summary they yield an analysis and a subsequent first guess which are in closer agreement with observations. the analysis scheme yields more balanced fields in the sense that the subsequent initialization produces more modest changes. the major impact on forecasts, in particular in the short range, is also judged to be positive. These improvements have been incorporated in the ECMWF operational data assimilation system. They have also been incorporated in the reassimilation of the final FGGE level IIb data set at ECMWF.

Data Assimilation: the 1984/85 Revisions of the Ecmwf Mass and Wind Analysis

AbstractA comprehensive evaluation of the ECMWF operational data assimilation system has been made, based largely on statistics of its performance over a long period of time. the evaluation has identified many deficiencies, covering such aspects of the analysis as the optimum interpolation statistics, the data selection algorithms, and the quality control criteria applied within the analysis.The observation and forecast error variances were seriously in error in the stratosphere and in the tropics. A more faithful model of the forecast error spectrum is provided by the Bessel function expansion than by the Gaussian model. the vertical structure of the height error is assumed to be composed of two components: a ‘barotropic’ part related to a horizontally constant mode and a ‘baroclinic’ structure for the horizontally varying modes. the wind field errors also have a large‐scale component. the extratropical vertical correlation remained similar to the earlier correlations, but the tropical height and wind structures changed dramatically.Reasonable rejection limits were defined from the distributions of the observation departures from the first guess, as were observation errors for satellite and aircraft wind reports and Australian pseudo‐observations.A comprehensive and homogeneous data selection algorithm has been devised. However, it has been found necessary to exclude land surface wind reports from the analysis process as the wind departures from a first‐guess field commonly contradict the surface pressure departures due to difficulties in generating a reasonable 10 m first‐guess wind. the omission of surface winds alleviated the data selection problem in data‐dense regions.The representation of the vertical correlations was changed to a continuous representation in the vertical which enabled a multivariate interpolation from data on standard pressure levels directly to model coordinates. the earlier procedure used a multivariate interpolation to constant pressure surfaces in the model grid, followed by a univariate interpolation to model surfaces in the vertical.The results of these improvements, in a series of tests covering in total some 30 days of assimilations, are also described. In summary they yield an analysis and a subsequent first guess which are in closer agreement with observations. the analysis scheme yields more balanced fields in the sense that the subsequent initialization produces more modest changes. the major impact on forecasts, in particular in the short range, is also judged to be positive.These improvements have been incorporated in the ECMWF operational data assimilation system. They have also been incorporated in the reassimilation of the final FGGE level IIb data set at ECMWF.

気象庁全球予報解析システムにおける衛星観測データの影響

An Observing System Experiment was carried out using the JMA global forecast/analysis system and the FGGE Main Level II-b data sets. Parallel sets of analyses and 5-day forecasts were produced for the three observing system configurations and the impact of the space based observing system was statistically and synoptically evaluated.Space based data are indispensable for the analyses in low latitude and the southern hemisphere. Even in the northern hemisphere, satellite data improve the analysis over the Pacific region and thereby improve the forecast over North America downstream of that region. The impact on the analysis at a certain time level appears as the sum of the impact of data existing at that time and the impact of data from previous time levels assimilated through the analysis and forecast cycles. On the other hand, satellite data have little impact on the forecast around East Asia because sonde data basically determine the quality of the analysis upstream of that region.

Data sensitivities of sea ice drift and ocean stress in North Atlantic high latitudes

Experiments with a limited‐area objective analysis are used to determine the effects of various data sources on surface stress and sea ice drift in North Atlantic high latitudes during a 7‐day period of the First GARP Global Experiment (FGGE). The objectively analyzed fields provide the input to a planetary boundary layer model, which provides the surface wind stresses for the forcing of a dynamic‐thermodynamic sea ice model. Different combinations of drifting buoy, surface marine, and satellite sounder data are deleted from the FGGE level IIB data input. On individual days the stresses are found to differ by as much as 50–100% and the ice drift speeds by as much as 10–15 km d−1 when buoy reports are deleted from the observing network. Seven‐day mean differences of the ice drift speeds are 3–5 km d−1 in some regions. The deviations from the “complete data” results are larger when both buoy/marine and satellite data are deleted than when only one type is deleted. While the high‐latitude sensitivities to satellite data are generally smaller than to buoy/marine data in the period considered here, large differences in ocean surface stress occasionally result from subtle effects of satellite data on the static stability of the near‐surface region. The results also show how data sensitivities can be exaggerated by the imposition of data rejection criteria in experiments utilizing consistent sets of guess fields and input data. The ice velocities obtained from the various experiments are compared with the available buoy displacements and with changes in the ice edge deduced from the Navy/NOAA weekly ice analyses.

The response of numerical weather prediction systems to fgge level iib data. Part I: Analyses

AbstractWe present an intercomparison of analyses of the main FGGE level IIb dataset with three advanced analysis systems. the aims of the work are to estimate the extent and magnitude of the differences between the analyses; to identify the reasons for the differences; and, finally, to estimate the significance of the differences for forecast skill. We restrict ourselves primarily to a consideration of the extra‐tropical analyses. the subject of tropical analyses merits separate treatment.We discuss objective evaluations of analysis quality, such as fit to observations, statistics of analysis differences, and mean fields. In addition we place substantial emphasis on subjective evaluation of a series of case studies which were selected to illustrate the importance of different aspects of the analysis procedures, such as quality control, data selection, resolution, dynamical balance, and the role of the assimilating forecast model. In some cases the forecast models are used as selective amplifiers of analysis differences to assist in deciding which analysis was more nearly correct in the treatment of particular data. In part II we consider the overall impact of the analysis differences on forecast quality, and the implications for predictability.In general the analysis systems draw reasonably well to the data, although each system has its own characteristics in this regard. the root mean square differences between the analyses are of the expected order of magnitude, although there are clear differences in the closeness of agreement between different pairs of analyses. Systematic differences arising from particular components of the assimilation suites can be identified.The discussion of the case studies highlights those areas where differences of approach to the analysis problem have led to significant differences in the analyses. Some of the case studies suggest strongly that analysis differences in the vicinity of active baroclinic zones are of particular importance. In order to validate these suggestions in one case, we present an experiment where one analysis is transplanted, locally, into another, to show that large differences in the medium‐range forecasts are attributable to localized differences in the analyses.The results presented here, together with the forecast verification results of part II, suggest that in some cases uncertainties in the analysis are a major contributor to the loss of forecast skill in the medium range.

The response of numerical weather prediction systems to fgge level iib data. Part II: Forecast verifications and implications for predictability

AbstractThe purpose of our two‐part study is to assess the importance of the differences between three independent analyses of the same FGGE level IIb observational dataset. Part I is concerned with the nature and origin of the differences among the analyses. Part II of the study is concerned with the implications of the analysis differences for forecast skill, and for estimates of predictability.Our experimental material is a set of forecasts by two models from the three ensembles of analyses. the energetics of the analyses are different, and this is reflected in differences in the energetics of the forecasts based on the analyses.A study of the objective forecast verifications shows that there are clear differences in the forecast skill of the two models we used. the verifications also show a marked sensitivity to the choice of initial data.We studied in some detail how forecasts made with the same model from different analyses diverge from one another, with particular attention to three aspects: (i) the growth rate at small amplitude; (ii) the time taken for the differences to reach an asymptotic level; (iii) the amplitude of this level relative to that of persistence. the results for small amplitude growth rates are consistent with earlier results in giving a doubling time of 2·0 days in the height field in the day 1‐2 forecasts but with slower growth rates (doubling times of 2·6 days) in the wind field. the baroclinic waves show faster growth, with about 0·25 days shorter doubling times. the forecast differences reach an asymptotic level more rapidly in this than in earlier investigations. This suggests that earlier estimates of the purely dynamical potential for predictability of instantaneous weather patterns may be overoptimistic.We combined the measures of forecast skill and forecast divergence in an error budget which separated the contributions to forecast error arising from model error and analysis error, subject to some simplifying assumptions. the results show that between day 2 and day 5 the model error grows linearly in time and the analysis error grows exponentially. the model is the main source of forecast error in this time range. the analysis error is the main source of forecast error in the short‐range forecasts, and is a substantial contributor after about day 5. These results are very sensitive to the magnitude of the initial analysis errors.Taken together with the synoptic results of part I, these statistical results emphasize the importance of analysis technique for the success of forecasting, particularly in the medium range. Given identical data of good quality, three advanced analysis systems produced analyses which lead to rather different forecasts.The results are based on a small sample over a period of 21/2 days, which represent essentially the same synoptic situation; therefore the generality of the results should be tested on further experiments.

The response of numerical weather prediction systems to FGGE level IIb data. Part I: Analyses

The response of numerical weather prediction systems to FGGE level IIb data. Part I: Analyses

The response of numerical weather prediction systems to FGGE level IIb data. Part II: Forecast verifications and implications for predictability

The response of numerical weather prediction systems to FGGE level IIb data. Part II: Forecast verifications and implications for predictability

The Large-Scale Circulation and Heat Sources over the Tibetan Plateau and Surrounding Areas during the Early Summer of 1979. Part II: Heat and Moisture Budgets

Abstract The large-scale heat and moisture budgets over the Tibetan Plateau and surrounding area during a 40-day period from late May to early July 1979 are studied using the FGGE Level II-b data. During this period the general circulation over East Asia underwent a distinct seasonal change characterizing the onset of the summer monsoon circulation. The analyses of the horizontal distributions of the vertically integrated heat source and moisture sink reveal the major heat source regions and their different degrees of association with precipitation. The 40-day mean distributions show intense heat sources of 150–300 W m−2 with moisture sinks of nearly equal magnitude over the Assam–Bengal region and in a broad belt extending over the China Plain along the Mei-yu front. The heat source of ∼100–150 W m−21 over the eastern Tibetan Plateau is accompanied by a moisture sink with a magnitude about half as large. The heat sources over the western Plateau and the Takla Makan Desert are not accompanied by appreciab...

The Large-Scale Circulation and Heat Sources over the Tibetan Plateau and Surrounding Areas during the Early Summer of 1979. Part I: Precipitation and Kinematic Analyses

The time evolution of the large-scale precipitation, low-level (850 mb) wind, moisture and vertical motion fields over the Tibetan Plateau and surrounding areas during a 40-day period from late May to early July 1979 is studied based on the objectively analyzed FGGE Level II-b data set. During this period the general circulation over East Asia undergoes a distinct change characterizing the onset of the summer monsoon circulation. The Tibetan Plateau exerts profound orographic and thermal influences upon the low-level wind field. The inflow towards the eastern part of the Plateau with a marked diurnal change in its intensity is the most prominent feature of the low-level wind field. The areas of organized precipitation are well related to synoptic systems seen in the 850 mb flow: the quasi-stationary Burma-India trough, the disturbances forming on the trough, the “Mei-yü (Baiu)” front, and the “transverse trough” extending eastward from the Plateau. There is a sharp contrast between the western and eastern Plateau in terms of precipitation and moisture distributions. The eastern Plateau acts as a huge chimney funneling water vapor from the lower to the upper troposphere. Maxima of 40-day mean upward velocities are located above the eastern Plateau, above the Assam-Bengal region and along the Mei-yü frontal zone. The vertical motions above the Plateau are more upward in the evening than in the morning. The reverse is true in the surrounding areas. Detailed examinations of daily values of the areal mean vertical p-velocity, mixing ratio and rainfall are made for four heat source regions (the western Plateau and adjacent areas, the eastern Plateau, the Yangzi River, the Assam-Bengal region) as a preliminary to the discussion of heating mechanisms operating in these regions.

U.S. FGGE special data sets and special effort

Three topics are considered, all resulting from the desire to maximize the utilization and overall quality of the FGGE data sets. First, the production of Level III-b oceanographic and meteorological analyses in the FGGE format has been undertaken by the Fleet Numerical Oceanography Center. The oceanographic data, in particular the sub-surface oceanographic data, is a unique addition to the FGGE data base. Next, the FGGE Level II-b data set is the most comprehensive set of synoptic-scale meteorological data ever assembled to date. Under development is a program aimed at compacting and restructuring the Level II-b data according to observing systems, so that the data will be more readily usable and more economical for users interested in smaller and/or different portions of the total FGGE Level II-b data set. Lastly, as a result of the United States pre-FGGE Data Systems Tests, a need was indicated for a special effort to edit and enhance satellite soundings and cloud motion wind data during FGGE. A formal program to carry out such an effort has been established jointly by NASA, NOAA, and the University of Wisconsin.

Vertical mass and moisture structure from TIROS-N

During the First Global GARP Experiment (FGGE), global determinations of mass and moisture were made from TIROS-N (and NOAA-6) infrared and microwave sounding radiance measurements. At NESS in Washington, the meteorological data were produced operationally with a horizontal resolution of 250 km for inclusion in the FGGE level II-b data sets intended for application to large scale numerical analysis and prediction models. High horizontal resolution (50 km) sounding data sets are being produced by NESS and the Space Science and Engineering Center at the University of Wisconsin and at the NASA/Goddard Space Flight Center for special case studies of the “Special Observing Periods” of FGGE. Results are presented to display the characteristics of the sounding data at different resolutions. For the low horizontal resolution data, an evaluation is shown by comparisons of global analyses made only from satellite soundings over land and sea, and those made operationally by the National Meteorological Center, which excluded satellite sounding data over continental areas, but included all conventional data sources. For the high horizontal resolution sounding data, results are presented to demonstrate the delineation of small scale temperature and moisture features which are consistent with the meteorological processes involved.

Numerical simulation—assessment of FGGE data with regard to their assimilation in a global data set

The data-assimilation system at the European Centre for Medium Range Forecasts (ECMWF) is presented. The data assimilation system is used to process the FGGE level II-b data and to provide global 3-dimensional analyses for every 6th hour through the whole FGGE year. The quality and the excellent coverage of the data has meant a substantial improvement in our understanding of the global atmosphere with major implication for climate and extended weather forecasting. Results from an observing system experiment only using data observed and collected from space is presented. It is found that fully space-oriented systems are possible although forecast quality is higher in areas where radiosondes are available with a satisfactory density.