UK Meteorological Office UARS Assimilated Data Held at the British Atmospheric Data Centre

Data assimilation is the approach used to analyse a heterogenous
mixture of observations distributed in space and time. Assimilation
is essentially an analysis technique that fits a model to observed data.
The model (in this case a numerical forecast model of the stratosphere
and troposphere) provides a strong constraint to the analysis problem,
i.e. the model ensures that the analysed fields are reasonably
self-consistent.

The system was developed from the United Kingdom Meteorological
Office's data assimilation scheme for operational weather forecasting,
where the forecast model at the heart of the system is capable of being
run at many different resolutions. For the UARS project it is configured
so that its vertical coverage extends from the earth's surface to above
the stratopause.

The numerical model used is a global primitive equation model, with
a split-explicit time integration scheme, and incorporates a comprehensive
range of physical parametrization schemes.

It uses a hybrid vertical coordinate system, with a terrain-following
model at low levels, gradually changing to pressure levels in the
stratosphere.

The observations used as input to the assimilation are essentially the
same as those used for operational weather forecasting i.e. the World
Weather Watch network of surface and upper air observations and
satellite data.

Two sets of assimilated data are/will be available:

1) A correlative assimilation experiment is run close to real time;
this is based on the observations mentioned above. Fields from this
experiment are available to allow UARS investigators to check their
retrievals against an independent analysis (ie temperature,
geopotential-height, and zonal, meridional and vertical-winds.

All fields are specified on a 2.5 (degrees latitude) x 3.75 (degrees
longitude) "Arakawa B" global grid - the grid of winds is staggered by
half a grid point relative to the grid of temperatures and geopotential
heights - and interpolated on to the standard (22) UARS pressure levels,
(1000 -> 0.316 HPa inclusive), equivalent to approximately 0 -> 55km.
The vertical resolution in the stratosphere is about 1.6 km.

2) Experiments assimilating UARS data, in addition to the standard
meteorological observations, will also be run. These will not form a
continuous sequence, instead we will run different experiments to
assimilate particular combinations of data from different instruments.
The system will first be used to assimilate temperature data from ISAMS;
next, wind measurements from HRDI will be assimilated. At a later stage,
the system will also be used to assimilate chemical species (initially
treating long-lived species as tracers).

Formats

The online data is held both in its original VAX binary format and
in compressed ASCII form (for portability). IEEE binary data is made
available on CD ROMs. Software to support these formats is available,
along with a library of UKMO access routines - including code to produce
Ertel Potential Vorticities across isentropic surfaces. This software
has been tested on a number of Unix operating systems and VMS, and efforts
have been made to reduce other portability problems. The language used
throughout is FORTRAN.

Extensive documentation for the datasets and the support software is
available at the BADC.

Additional Data

There is a considerable amount of additional data, including short
contiguous periods of assimilations at six-hourly intervals - consult the
BADC catalogues for details.

Value-added data products produced by the BADC comprise complete
sets of global and zonal monthly averages, with the ability to produce
- upon demand - averaged data for any period.

You MUST register with the BADC in order to access UKMO data.

Data_Set_Progress: Ongoing update (10 days behind real-time)