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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.