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William G. Collins

Abstract

The adjustment properties of numerical models are important both from the Point of view of the handling of noise and the ability to produce proper quasi-geostrophic states from physically derived imbalances between mass and motion fields. This paper considers the adjustment properties of simplified barotropic one-dimensional numerical models with explicit and semi-implicit time differencing.

The classical Rossby adjustment problem provides the framework for comparison with the numerical results. In addition, linear analysis of the models provides useful insight. Primary emphasis is on the time required for adequate adjustment and the accuracy of the adjusted state. The adjustment time increases with the scale of the initial disturbance, and does not differ significantly between the explicit and semi-implicit models. The grid increment is one of the dominant factors in determining the adjustment time. Both models accurately calculated the final adjusted state.

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William G. Collins

Abstract

The quality control of meteorological data has always been an important, if not always fully appreciated, step in the use of the data for analysis and forecasting. In most quality-control approaches, erroneous data are treated as nonrandom “outliers” to the data distribution, which must be eliminated. The elimination of such data traditionally proceeds from coarse to finer filters. More recent methods use the fit (or lack of fit) of such data to an analysis, excluding the data, to determine whether data are acceptable. The complex quality-control (CQC) approach, on the other hand, recognizes that most rough errors are caused by human error and can likely be corrected. In the CQC approach, several independent checks are made that provide numerical measures of any error magnitude. It is only after all check magnitudes, called residuals, are calculated that data quality is determined and errors are corrected when possible. The data-quality assessment and correction is made by the sophisticated logic of the decision-making algorithm (DMA). The principles and development of the method of CQC for radiosonde data were given by Gandin. The development of CQC at the National Centers for Environmental Protection (NCEP) for the detection and correction of errors in radiosonde heights and temperatures, called the complex quality control for heights and temperatures (CQCHT), has progressed from the use of a complex of hydrostatic checks only to the use of statistical and other checks as well, thereby becoming progressively sophisticated. This paper describes a major restructuring in the use of the radiosonde data and in the logical basis of the DMA in the operational CQCHT algorithm at NCEP so that, unlike the previous implementations, all data levels are treated together, thus potentially allowing the correction at any level to influence subsequent correction at adjacent levels, whether they are mandatory or significant. At each level, treated one by one from the surface upward, all available checks are used to make the appropriate decisions. Several vertical passes may be made through the data until no more corrections are possible. Final passes look for “observation” errors. The methods of error determination are outlined, and the effect of errors on the residuals is illustrated. The calculation of residuals is described, their availability for each type of data surface (e.g., earth’s surface, mandatory level, significant level) is given, and their use by the DMA is presented. The limitations of the use of various checks are discussed.

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William G. Collins

Abstract

The method of complex quality control of radiosonde heights and temperatures (CQCHT) has been under continuous development and improvement at the National Centers for Environmental Prediction since 1988. Part I of this paper gives the background for the method and details for the currently operational version of the code, which contains significant improvements over previous versions. Part II shows a number of interesting examples of operation of the algorithm and gives statistics on its performance during the first year of operation, September 1997 through August 1998. In a few examples, it is seen how even complicated errors may be corrected. The statistics show that of the 5700 hydrostatically detected errors each month, 77% were corrected. There is a great variation in the geographical distribution of errors, but it is found that a majority of all stations have at least one hydrostatically suspected error during a month’s time. In addition to hydrostatically detected errors, the CQCHT detects almost 16 000 so-called observation errors in height and temperature each month.

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William G. Collins

Abstract

Rawinsonde heights and temperatures have been quality controlled using complex quality control at the National Centers for Atmospheric Prediction since December 1988 when an algorithm using only hydrostatic checking was introduced for the checking of mandatory level heights and temperatures. The quality control of significant level temperatures was added to the hydrostatic code in April 1990. In November 1991, the mandatory level checking was greatly expanded and improved by the inclusion of additional checks: increment (observation minus 6-h forecast), horizontal, and vertical. This paper describes a major improvement to the significant level quality control, introduced in May 1994, using complex quality control techniques. The philosophy of the method and the various checks are described. The principles of the decision-making algorithm are stated, examples are shown, and some statistics of the use of the significant level checking are presented.

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William G. Collins
and
Lev S. Gandin

Abstract

The Comprehensive Hydrostatic Quality Control (CHQC) of rawinsonde data on height and temperature at mandatory isobaric surfaces designed and implemented at the National Meteorological Center in Washington is described in detail. Main principles of the quality control design are discussed, followed by a brief description of the CHQC design and implementation at NMC. The CHQC algorithm is presented with particular emphasis on the Decision Making Algorithm. Numerous examples taken from the operational CHQC outputs illustrate the CHQC performance in general as well as its reaction to errors of various types and to their combinations.

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Kyle G. Pressel
and
William D. Collins

Abstract

The power-law scale dependence, or scaling, of first-order structure functions of the tropospheric water vapor field between 58°S and 58°N is investigated using observations from the Atmospheric Infrared Sounder (AIRS). Power-law scale dependence of the first-order structure function would indicate that the water vapor field exhibits statistical scale invariance. Directional and directionally independent first-order structure functions are computed to assess the directional dependence of derived first-order structure function scaling exponents (H) for a range of scales from 50 to 500 km. In comparison to other methods of assessing statistical scale invariance, the methodology used here requires minimal assumptions regarding the homogeneity of the spatial distribution of data within regions of analysis. Additionally, the methodology facilitates the evaluation of anisotropy and quantifies the extent to which the structure functions exhibit scale invariance.

The spatial and seasonal dependence of the computed scaling exponents are explored. Minimum scaling exponents at all levels are shown to occur proximate to the equator, while the global maximum is shown to occur in the middle troposphere near the tropical–subtropical margin of the winter hemisphere.

From a detailed analysis of AIRS maritime scaling exponents, it is concluded that the AIRS observations suggest the existence of two scaling regimes in the extratropics. One of these regimes characterizes the statistical scale invariance the free troposphere with H approximately = 0.55 and a second that characterizes the statistical scale invariance of the boundary layer with H approximately = ⅓.

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LLOYD W. VANDERMAN
and
WILLIAM G. COLLINS

Abstract

A primitive equation barotropic forecast model is employed independently at 700 mb. and 300 mb. to produce a wind forecast to 36 hr. once daily (from 1200 gmt real data analyses) for the entire tropical belt between 48°N. and 48°S. Experiments have been made in calculating with tropical barotropic forecast models taking values along the northern boundary from a previously calculated Northern Hemisphere forecast. Descriptions of the forecast models and examples and verifications of the forecasts are presented.

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Lev S. Gandin
,
Lauren L. Morone
, and
William G. Collins

Abstract

A comprehensive hydrostatic quality control (CHQC) procedure for rawinsonde heights and temperatures was implemented into operational use at the National Meteorological Center (NMC) in December 1988. The CHQC uses a sophisticated decision-making algorithm to detect so-called rough errors in rawinsonde observations and to confidently correct many of them. Statistics gathered over a two-year period are presented to provide information on the frequency, geographical distribution, and origin of these errors. During this period, approximately 7% of the rawinsonde reports received at the NMC contained a hydrostatically detectable error. The number of errors has stayed relatively constant over the two-year period. The geographic distribution of the errors is uneven, with most of them originating in countries where many of the steps involved in computing and coding the reports are performed manually. Other characteristics as well indicate that almost all problems that are detected by the CHQC are caused by human error. This article proposes several measures as a means of reducing these errors. An analysis of the performance of the CHQC, which reveals that fully 50% of the errors that are detected by the CHQC are corrected automatically by it as well, is also presented. Information about the remaining errors along with suggested corrections is made available to specialists in NMC's Meteorological Operations Division where a final decision is made. This type of information has been discovered to also be quite useful in monitoring the quality of data in near-real time. Its use has led to a quick resolution of many problems associated with data transmission and decoding procedures. Several examples are discussed.

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HAROLD A. BEDIENT
,
WILLIAM G. COLLINS
, and
GLORIA DENT

Abstract

This paper presents the results of 5 months of an experimental operational tropical analysis scheme. The grid is a 5° of longitude square on a Mercator map. The array size is 72×23 or approximately 48°N. to 48°S. completely around the earth. The analysis has been firmly meshed into the high latitude analysis and is made at the 700-, 500-, 300-, 250-, and 200-mb. levels.

The scheme is similar to that reported by Bedient and Vederman. The current output fields are the wind and streamfunction. Pressure and temperature will be added. In conjunction with the analysis an effort has been made to increase the input of aircraft data and to improve quality control and the results will be shown. Some experiments have been made in using satellite cloud pictures to improve analysis in poor data areas. This can be of special benefit in getting a proper description of the Southern Hemisphere westerlies.

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Kenneth S. Gage
,
John R. McAfee
,
William G. Collins
,
Daniel Söderman
,
Horst Böttger
,
Alan Radford
, and
Ben Balsley

Wind profilers can provide useful wind data from remote regions of the globe, and incorporation of upper-level wind profiler data into analysis products can significantly improve the quality of analyses in data sparse regions.

A wind-profiling Doppler radar was installed by the Aeronomy Laboratory on Christmas Island during late 1985 as part of the Tropical Ocean Global Atmosphere (TOGA) Program. The Christmas Island profiler is self-contained and operates essentially unattended. Since April 1986, data from the Christmas Island profiler have been tele-metered via GOES Satellite to provide hourly-averaged soundings of the wind four times daily keyed to the standard synoptic observing times and incorporated routinely onto the Global Telecommunication System (GTS) for world-wide distribution.

In 1987 both NMC and ECMWF began using Christmas Island wind profiler observations in preparing their global analysis and forecast products. Detailed comparisons of NMC and ECMWF analyses with Christmas Island winds before and after profiler winds were introduced into the global analyses are presented. Results of statistical comparisons reveal a marked improvement in the analyses following the introduction of Christmas Island winds into the standard analysis products: before the Christmas Island winds were introduced into the analyses, monthly mean standard deviations between analyzed and observed winds were typically in the range 3–5 m · s−1 and monthly mean biases were typically in the range 1–3 m · s−1; after the Christmas Island winds were introduced, the standard deviation was reduced to about 1–2 m · s−1 at most heights, while the bias values were reduced to less than 0.5 m · s−1 at most heights.

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