Impact of ATOVS> Selected Papers

Selected paper abstracts on impact of ATOVS in NWP

Zhang H, Xue JS, Zhu GF, Zhuang SY, Wu XB, Zhang FY, 2004: Application of direct assimilation of ATOVS microwave radiances to typhoon track prediction. 
ADVANCES IN ATMOSPHERIC SCIENCES 21 (2): 283-290 MAR 2004

Abstract: In order to solve the difficult problem of typhoon track prediction due to the sparsity of conventional data over the tropical ocean, in this paper, the No. 0205 typhoon Rammasun of 4-6 July 2002 is studied and an experiment of the typhoon track prediction is made with the direct use of the Advanced TIROS-N Operational Vertical Sounder (ATOVS) microwave radiance data in three-dimensional variational data assimilation. The prediction result shows that the experiment with the ATOVS microwave radiance data can not only successfully predict the observed fact that typhoon Rammasun moves northward and turns right, but can also simulate the action of the fast movement of the typhoon, which cannot be simulated with only conventional radiosonde data. The skill of the typhoon track prediction with the ATOVS microwave radiance data is much better than that without the ATOVS data. The typhoon track prediction of the former scheme is consistent in time and in location with the observation. The direct assimilation of ATOVS microwave radiance data is an available way to solve the problem of the sparse observation data over the tropical ocean, and has great potential in being applied to typhoon track prediction.

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Langland RH, Baker AL, 2004: Estimation of observation impact using the NRL atmospheric variational data assimilation adjoint system.
TELLUS SERIES A-DYNAMIC METEOROLOGY AND OCEANOGRAPHY 56 (3): 189-201 MAY 2004

Abstract: An adjoint-based procedure for assessing the impact of observations on the short-range forecast error in numerical weather prediction is described. The method is computationally inexpensive and allows observation impact to be partitioned for any set or subset of observations, by instrument type, observed variable, geographic region, vertical level or other category. The cost function is the difference between measures of 24-h and 30-h global forecast error in the Navy Operational Global Atmospheric Prediction System (NOGAPS) during June and December 2002. Observations are assimilated at 00UTC in the Naval Research Laboratory (NRL) Atmospheric Variational Data Assimilation System (NAVDAS). The largest error reductions in the Northern Hemisphere are produced by rawinsondes, satellite wind data, and aircraft observations. In the Southern Hemisphere, the largest error reductions are produced by Advanced TIROS Operational Vertical Sounder (ATOVS) temperature retrievals, satellite wind data and rawinsondes. Approximately 60% (40%) of global observation impact is attributed to observations below (above) 500 hPa. A significant correlation is found between observation impact and cloud cover at the observation location. Currently, without consideration of moisture observations and moist processes in the forecast model adjoint, the observation impact procedure accounts for about 75% of the actual reduction in 24-h forecast error.

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Ahn MH, Kim MJ, Chung CY, Suh AS, 2003: Operational implementation of the ATOVS processing procedure in KMA and its validation.
ADVANCES IN ATMOSPHERIC SCIENCES 20 (3): 398-414 MAY 2003

Abstract:
 The Korea Meteorological Administration (KMA) has processed the data from the advanced TOVS (ATOVS) onboard NOAA-16 satellite since May 2001. The operational production utilizes the AAPP (ATOVS and AVHRR Processing Package) of EUMETSAT and IAPP (International ATOVS Processing Package) of the University of Wisconsin. For the initial guess profiles, the predicted fields (usually 6 to 12 hour forecasted fields) from the global aviation model of NOAA/NCEP are used. The average number of profiles retrieved from the ATOVS data is about 1,300 for each morning and afternoon orbit at about 18 and 06 UTC, respectively. The retrieved temperature and dew point temperatures are provided to forecasters in real time and used for initialization of prediction models. With the advanced microwave sensor (AMSU; Advanced Microwave Sounding Unit), accuracy of the ATOVS products is expected to be better than that of the TOVS products, especially in cloudy conditions. Indeed, the preliminary results from a validation study with the collocated radiosonde data during a 8-month period, from May to December 2001, for the East Asia region show an improved accuracy of the ATOVS products for cloudy skies versus the TOVS, especially for higher altitudes. The RMS (Root Mean Square) difference between the ATOVS products and radiosonde data is about 1.3 C for both clear and cloudy conditions, except for near the ground and at higher altitudes, at around 200 hPa. There is no significant temporal variation of the error statistics at all pressure levels. In case of the water vapor mixing ratio, the largest difference is shown at lower altitudes, while the accuracy is much better for the clear sky cases than the cloudy sky cases. The bias and RMSE at lower altitudes is about 0.557 g kg(-1) and 2.5 g kg(-1) and decrease significantly with increasing altitude.

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Fourrie N, Doerenbecher A, Bergot T, Joly A, 2002: Adjoint sensitivity of the forecast to TOVS observations.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 128 (586): 2759-2777 Part B, OCT 2002

Abstract: The adjoint sensitivity to observations which is based on the adjoint operator of the variational assimilation process is used here on ten cases of the Fronts and Atlantic Storm-Track Experiment (FASTEX), conducted in January and February 1997. It is used as a diagnostic tool allowing one to indicate which TIROS-N (Television Infrared Observation Satellite) Operational Vertical Sounder (TOVS) channels have an influence on the forecast of mid-latitude lows. In order to study the effects of the observations on the modification of the forecast from the guess, a particular cost function has been chosen: the energy of the difference between the forecast derived from the guess and the one resulting from the analysis. The first part of the paper deals with the sensitivity to the assimilated TOVS observations for the intensive observation period 17 of FASTEX. Then, the influence of TOVS data is compared with one of the other conventional datasets assimilated at the same time. After that, these results are generalized in an overview of the ten studied cases. This study highlights that the Microwave Sounder Unit and clear sky or partly cloudy High-resolution Infra-Red Sounder have the larger influence of the TOVS observations on the modification of the forecast. However, the other conventional data have a larger absolute contribution than the TOVS ones.

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Le Marshall JF, Seecamp R, Harris B, Tingwell C, Kelly G, 2001: First results from the use of local ATOVS data in the Australian region
AUSTRALIAN METEOROLOGICAL MAGAZINE 50 (2): 159-163 JUN 2001

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Bouttier F, Kelly G, 2001: Observing-system experiments in the ECMWF 4D-Var data assimilation system.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 127 (574): 1469-1488 Part B, APR 2001

Abstract:
 A set of global observing-system experiments is run by excluding classes of observations from the European Centre for Medium-Range Weather Forecasts (ECMWF) four-dimensional variational (4D-Var) data assimilation and forecast system. This indicates how efficiently the observations are used in this particular system. The observing systems tested were mainly TIROS (Television Infra-Red Observation Satellite) Operational Vertical Sounder (TOVS) radiances. SATellite OBservation (SATOB) atmospheric-motion winds, radiosondes, aircraft, drifting buoys and Australian pseudo observations (PAOBs). The impact is assessed in both summer and winter 1999, over a total period of six weeks, in terms of the average objective quality of the deterministic forecast of tropospheric wind and geopotential height at medium (5-7 day) and short (1-3 day) ranges. It is shown that the choice of verification method matters in data-poor areas such as the tropics and the southern hemisphere. Some interesting conclusions can be drawn about the ECMWF 4D-Var system. Each observing system tested has a notable positive impact on the medium-range forecast performance. This is not always true at shorter ranges. The TOVS radiances have a large impact on all areas and ranges. Drifting buoys and PAOBs both have some impact in the southern hemisphere. In the northern hemisphere, the relative impact of TOVS, aircraft and radiosondes depends on the area considered. For Europe, the statistical significance of the results is limited, but the most important observing system among those tested appears to be the radiosondes.

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English SJ, Renshaw RJ, Dibben PC, Smith AJ, Rayer PJ, Poulsen C, Saunders FW, Eyre JR, 2000: A comparison of the impact of TOVS and ATOVS satellite sounding data on the accuracy of numerical weather forecasts.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 126 (569): 2911-2931 Part A, OCT 2000

Abstract: The Advanced TIROS Operational Vertical Sounder (ATOVS) was launched on the NOAA-15 satellite in May 1998. This provided a very significant improvement in the information available from meteorological polar-orbiting satellites compared with the previous TIROS Operational Vertical Sounder system, particularly for humidity and vertical resolution of temperature in cloudy areas. In preparation for assimilation of the observations into a three-dimensional analysis of atmospheric temperature and humidity, the observations have been compared with calculated top-of-atmosphere brightness temperatures computed from numerical weather prediction model profiles of temperature and humidity. Differences between observed and modelled brightness temperature are small. In some parts of the tropics and northern hemisphere the standard deviation of these differences for the tropospheric Advanced Microwave Sounding Unit sounding channels is only marginally higher than the radiometric noise of the observations. Early in 1999 a series of observation-system experiments were completed in which ATOVS observations were assimilated using a one-dimensional variational analysis. No use of the new humidity information could be made because of interference problems experienced by the microwave humidity sounder on ATOVS. Nonetheless, these experiments showed that the assimilation of the new temperature information provided by the radiance observations reduces forecast errors by as much as 20% in the southern hemisphere and 5% in the northern hemisphere. Further improvements have been found by assimilating more data over land. The major impact arises from the microwave channels. Whilst forward-model errors may be slightly lower for the microwave channels than the infrared channels the primary reason is the provision of sounding information in active weather systems, which are usually cloudy.

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McNally AP, 2000: Estimates of short-range forecast-temperature error correlations and the implications for radiance-data assimilation
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 126 (562): 361-373 Part A, JAN 2000

Abstract: The importance of an accurate specification of shea-range forecast-error structures for the successful assimilation of satellite sounding data is discussed, with special emphasis on the role of vertical tinter-level) error correlations. Two different statistical approaches for estimating these correlations are examined. The first is based on comparing radiosonde profiles with the short-range forecast. The second compares forecasts of different lengths which verify at the same time. It will be shown that, in some aspects, the two approaches produce consistent results which suggests that significant geographic and seasonal variability exists in the vertical error correlations. The effect of not modelling this variability in the analysis of TOVS (TIROS-N (Television Infra-Red Observation Satellite) Operational Vertical Sounder) radiance data is simulated using a linear retrieval estimator, and it is shown that it may result in a serious misinterpretation of the information in the observations.

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Chen MH, Rood RB, Joiner J, 1999: Assimilating TOVS humidity into the GEOS-2 data assimilation system.
JOURNAL OF CLIMATE 12 (10): 2983-2995 OCT 1999

Abstract: The humidity data retrieved from the TIROS Operational Vertical Sounder (TOVS) measurements is assimilated into the Goddard Earth Observing System (GEOS) data assimilation system. The study focuses on the impact of the TOVS humidity on assimilated humidity, precipitation, clouds, and radiation. The GEOS assimilation system utilizes the TOVS humidity effectively at levels below 300 mb, while the net impact on the 300-mb humidity is much less. It has been demonstrated that the impact results from direct and indirect effects. The direct effect is the analysis increment introduced by the humidity data, which draws the assimilated humidity toward the data. The indirect effect is realized through the interactions of humidity with physical processes, mainly with moist convection. The indirect effect is often opposite to the direct effect in the current assimilation system. The direct effect is dominant in the lower and middle troposphere while in the upper troposphere the indirect effect is more important. The impact of the TOVS humidity on the GEOS precipitation, clouds, and radiation is also significant due to strong interactions with convection and other physical processes. There is clear evidence indicating that tuning of physical parameterizations explicitly in the data assimilation mode is necessary for optimal use of the TOVS data in the assimilation system.

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Prasad VS, Ramesh KJ, Bohra AK, Bhatia RC, 1998: Assessment of quality and impact of full resolution TOVS temperature profile data on the operational global data assimilation forecast system of India.
METEOROLOGY AND ATMOSPHERIC PHYSICS 68 (3-4): 197-212 1998

Abstract: TOVS temperature profile data (SATEM) at its full resolution (85 km) has now become available in India on experimental basis. An attempt is made in this study to examine the quality and impact of this on the medium range forecasts over India and neighbourhood. For this purpose, a seven day period starting from 15 March 1996 is chosen to study the impact of the data on the global analysis-forecasting system operational in India. Though one week data is utilized for the impact study, the complete data of March 1996 is used for examining quality, representativeness and consistency of the retrievals. In the operational system of the National Centre for Medium Range Weather Forecasting (NCMRWF), all types of data, including coarse resolution (500 km) global TOVS retrievals-coarse grid SATEM (CGS) data, received on GTS at hourly intervals are used in the assimilation cycle. For the present study the assimilation cycle is repeated for the above period by including high resolution data over the geographical regions covered by the New Delhi's high resolution picture transmission (HRPT) station and simultaneously removing coarse resolution SATEM data. The analysis and forecast fields thus generated are compared with the corresponding operational archives. The impact of the data is examined in terms of various objective scores and through circulation characteristics. The study reveals that the quality of high resolution SATEM (HRS) data is satisfactory and is such that it can be utilized in the global data assimilation system on real-time basis. A general improvement in the RMSE and ACC scores of the medium range forecasts is found over the data void equatorial sectors of the Indian Ocean after the incorporation of the HRS data fields in the assimilation cycle. With regard to a typical easterly wave activity of moderate intensity during the period of experimentation, a marginal modulation in low level vorticity and divergence forecasts is found to be improving the precipitation magnitudes over the south peninsular India as well.

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Eyre JR, 1997:  Variational assimilation of remotely-sensed observations of the atmosphere JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 75 (1B): 331-338 MAR 1997

Abstract: 
This paper considers some of the problems that arise concerning the assimilation of remotely-sensed observations into numerical weather prediction models, including the options and compromises that have to be faced in deciding whether and how to pre-process the observations prior to assimilation. These issues are discussed first in general and then in relation to some specific observation types: TOVS radiances, satellite winds and cloud imagery, SSM/I data, scatterometer data and radio occultation data. Results of recent work in these areas at ECMWF are summarized or referenced.

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McNally AP, Vesperini M., 1996: Variational analysis of humidity information from TOVS radiances QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 122 (535): 1521-1544 Part A, OCT 1996

Abstract: The impact of assimilating TOVS radiance data in the European Centre for Medium-Range Weather Forecasts humidity analysis is evaluated. It has been found that the introduction of a one-dimensional variational analysis scheme (1DVAR) applied to the TOVSTOVS radiance data is discussed and found to be consistent with significant changes observed in the mid upper-tropospheric moisture fields when the radiance data are assimilated. In particular, a tendency of the model (without radiance assimilation) to produce a tropical humidity structure that is far too dry is removed, and excessively moist conditions in the southern sub-tropics are improved. It is argued that the latter problem originates from the use of operational NESDIS retrieved products in the analysis. The humidity adjustments caused by the assimilation of TOVS radiances are accompanied by significant changes in the model dynamics, especially the description of the tropical Hadley circulation. One such case is described in detail, where the moistening of the tropics and drying of the sub-tropics has resulted in a stronger mean analysed meridional circulation in the Atlantic. The analysis changes are also shown to improve the medium-range forecasting of humidity, together with some associated benefit in the prediction of cloud and precipitation.

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Gadd AJ, Barwell BR, Cox SJ, Renshaw RJ, 1995: Global processing of satellite sounding radiances in a numerical weather prediction system.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 121 (523): 615-630 Part A, APR 1995

Abstract: This paper gives an account of the global soundings system (GLOSS), which is the new method introduced at the Meteorological Office at Bracknell for the processing of global TOVS radiance data for assimilation into numerical weather prediction (NWP) models. The assimilating NWP models themselves provide the prior information necessary to infer temperature and humidity information from radiances. After a brief summary of the historical background, the GLOSS processing is described, noting in particular the differences from similar work elsewhere. Results are then presented from NWP impact studies of the assimilation of temperature profiles derived from satellite soundings. An advantage is demonstrated for the GLOSS temperature retrievals relative to the retrievals distributed by NESDIS and produced from the same radiance data. The advantage of GLOSS is clear and consistent in the extratropical regions of the northern hemisphere and, especially, of the southern hemisphere. In the tropics the results are more mixed. The paper concludes with a note of additional work required before operational implementation of GLOSS, and with an outline of other expected future developments.

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Andersson E, Pailleux J, Thepaut JN, Eyre JR, McNally AP, Kelly GA, Courtier P, 1994: Use of cloud cleared radiances in 3-dimenstional 4 dimensional variational data assimilation.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 120 (517): 627-653 APR 1994

Abstract: The direct use of TOVS (TIROS Operational Vertical Sounder) cloud-cleared radiances in a three/four-dimensional variational data assimilation scheme is described. This scheme uses a fast radiative transfer model and its adjoint. Radiances are used together with all the other observational data. Global spectral fields of mass, wind and humidity are analysed simultaneously under certain mass/wind balance constraints which control the degree to which gravity waves enter into the analysis. In this way the need for a subsequent initialization is avoided. The scheme thus combines retrieval, analysis and initialization in one step and makes it possible to achieve a more optimal combination of the information contained in the radiances, the conventional data and the background (a six-hour forecast). At spectral truncation T63, a global three-dimensional variational analysis (3D-Var) of TOVS radiances and conventional data is compared with the ECMWF operational Optimum Interpolation scheme, which uses TOVS radiance information in the form of profiles of temperature and humidity, retrieved using a one-dimensional variational method. The results of 3D-Var are in good agreement with the operational analysis at the same resolution. In an application of the four-dimensional scheme (4D-Var), data covering a period of 24 hours were used simultaneously. In 4D-Var consistency in time is ensured through the evolution of the forecast model and its adjoint. Using the adiabatic version of the ECMWF forecast model (spectral resolution T42) we show that 4D-Var is able to extract additional information from the dynamics of the model. In particular we show an impact on the tropical wind field from the use of the humidity-sensitive TOVS channels.

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Eyre JR, Kelly GA, McNally AP, Andersson E, Persson A, 1993: Assimilation of TOVS radiance information through one-dimenstional variational analysis.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 119 (514): 1427-1463 OCT 1993

Abstract: In recent years difficulties have been experienced in exploiting satellite sounding data in numerical weather prediction (NWP) in the form of independently retrieved temperature and humidity profiles. Attention has now focused on methods through which the information in the radiance measurements may be assimilated more directly into the NWP system. A scheme known as 'one-dimensional variational analysis' (1DVAR) has been developed at the European Centre for Medium-range Weather Forecasts as a method for extracting information from TIROS Operational Vertical Sounder radiances for use in the operational data-assimilation system. The 1DVAR scheme is based on variational principles applied to the analysis of the atmospheric profile at a single location, using a forecast profile and its error covariance as constraints. The details of the scheme are presented. Errors in 1DVAR products are correlated with those of the short-range forecast which serves as a background for the subsequent three-dimensional analysis. Methods for addressing this aspect of the assimilation problem are discussed.

The characteristics of 1DVAR products and their impact on the analysis are described. A series of forecast impact experiments has been conducted and has demonstrated consistent positive impacts on forecast skill in the northern hemisphere.

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Thepaut JN, Moll P, 1990: Variational inversion of simulated TOVS radiancs using the adjoint technique. QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 116 (496): 1425-1448 OCT 1990

Abstract: The adjoint technique allows the variational approach for assimilating various types of observations in meterology, including raw radiances measured by satellite, to be treated exactly and at a 'reasonable' cost. We have developed the tangent linear and adjoint operators of the International TOVS Processing Package radiative transfer equation. These two tools are used for treating two aspects of variational inversion of satellite sounding radiances. First of all, we apply this technique to the computation of the error covariance matrix of the retrieval/analysis of simulated TOVS sounding radiances. Using this matrix, an original method to interpret satellite sounding radiances in terms of temperature and humidity information is then presented. We can thus evaluate the number of independent parameters which are significantly estimated from radiances, given a direct radiative transfer model, observation and background error statistics. It is found that 19 HIRS channels provide six independent pieces of information while four MSU channels provide three independent pieces of information. When grouping HIRS and MSU channels, only seven independent pieces of information are available. It is shown that in cloudy conditions MSU channels bring additional significant information to HIRS channels especially at the surface. We also study the impact of cloudiness on the quality of the retrieved profiles.Numerical feasibility of 1-D variational inversion using the adjoint of the International TOVS Processing Package radiative transfer model is demonstrated. Impact of the choice of the inner product on the efficiency of the method is studied. We then discuss the quality of the inversion, which turns out to be strongly related to the quality of the atmospheric information present in the sounding radiances and to the background and observation error statistics. The gain brought by MSU channels at the surface in cloudy conditions is discussed.

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