J. R. Eyre

The Assimilation of Radio Occultation Measurements

GPS radio occultation (RO) measurements are a potentially important new source of profile information that can be used in numerical weather prediction (NWP). This paper outlines the options for assimilating the RO measurements into an operational NWP system. The importance of realistic estimates for the observation error estimates is discussed.

A New Method to Correct Radiosonde Temperature Biases Using Radio Occultation Data

AbstractA new method to estimate radiosonde temperature biases using radio occultation measurements as a reference has been developed. The bias is estimated as the difference between mean radio occultation and mean radiosonde departures from collocated profiles extracted from the Met Office global numerical weather prediction (NWP) system. Using NWP background profiles reduces the impact of spatial and temporal collocation errors. The use of NWP output also permits determination of the lowest level at which the atmosphere is sufficiently dry to analyze radio occultation dry temperature retrievals. The authors demonstrate the advantages of using a new tangent linear version of the dry temperature retrieval algorithm to propagate bending angle departures to dry temperature departures. This reduces the influence of a priori assumptions compared to a nonlinear retrieval. Radiosonde temperature biases, which depend on altitude and the solar elevation angle, are presented for five carefully chosen upper-air sit...

The Case for the Eumetsat Polar System (EPS)/Metop Second-Generation Programme: Cost Benefit Analysis

Observations from meteorological satellites are crucial inputs for the generation of weather forecasts and, in order to derive an estimate of the benefit-to-cost ratio of the polar-orbiting EPS/Metop-SG satellite programme proposed by EUMETSAT and ESA, an assessment of the socio-economic benefits of forecasts within the EU, in a number of key areas, is overlaid onto an analysis of the impact of polar-orbiting satellite observations on forecast skill, to produce a likely benefit-to-cost ratio of 20 for the proposed programme.

Characterising the background errors for the boundary-layer capping inversion

The one-dimensional variational assimilation of vertical temperature information in the presence of a boundary-layer capping inversion is studied. For an optimal analysis of the vertical temperature profile, an accurate representation of the back - ground error covariances is essential. The background error covariances are highly flow-dependent due to the variability in the presence, structure and height of the boundary-layer capping inversion. Flow-dependent estimates of the background error covariances are shown by studying the spread in an ensemble of forecasts. A forecast of the temperature profile (used as a background state) may have a significant error in the position of the capping inversion with respect to observa- tions. It is shown that the assimilation of observations may weaken the inversion structure in the analysis if only magnitude errors are accounted for as is the case for traditional data assimilation methods used for operational weather prediction. The positional error is treated explicitly here in a new data assimilation scheme to reduce positional error, in addition to the traditional framework to reduce magni- tude error. The distribution of the positional error of the background inversion is estimated for use with the new scheme.

Comparison of passive microwave sounding data with numerical weather prediction profiles

The Advanced Microwave Sounding Unit (AMSU), launched on May 13, 1998, is a twenty-channel passive microwave radiometer designed to provide information on atmospheric temperature and humidity structure in clear and cloudy conditions, complementing existing infra-red radiometers which provide information only in clear areas. AMSU has some channels similar to those flown on existing missions and others which are new. Observed radiances from the Special Sensor Microwave Imager (SSM/I) and the Microwave Sounding Unit (MSU) are compared with radiances calculated from numerical weather prediction (NWP) model profiles, and the differences discussed. A processing method for ATOVS radiances is described, and differences from previous techniques are highlighted. An initial evaluation of AMSU data is given. Finally the impact of passive microwave observations on the skill of numerical weather forecasts is discussed.