R. Brugge

Assimilation of ozone profiles and total column measurements into a global general circulation model

[1] Ozone profiles from the Microwave Limb Sounder (MLS) instrument flown on board the Upper Atmosphere Research Satellite (UARS) and total ozone columns measured by the Global Ozone Monitoring Experiment (GOME) on board the Second European Remote Sensing Satellite (ERS-2) have been assimilated using a troposphere-stratosphere data assimilation system. The analysis system is based on the global analysis system used for operational analysis of the stratosphere at the Meteorological Office from 1991 to 2000. Three assimilation runs have been completed for a three-week period in April 1997 to test the advantage of using a combination of MLS and GOME observations, compared with the assimilation of each observation data set separately. The statistical information produced by the assimilation system shows that the combination of MLS and GOME observations via the assimilation process produces ozone fields that show improvement compared with analysis fields produced by the assimilation of either MLS or GOME separately. Comparison of the analyzed ozone fields with independent observations (ozonesondes, Halogen Occultation Experiment (HALOE) profiles and Total Ozone Mapping Spectrometer (TOMS) total ozone column measurements) corroborates these results and shows that the combined MLS and GOME ozone analyses provide a realistic representation of the atmospheric ozone distribution. The global root-mean-square residual (difference between the analyses and independent observations) against HALOE and TOMS observations is comparable to the quoted errors in the HALOE and TOMS instruments (5% in each case).

Non-Hydrostatic Ocean Modelling for Studies of Open-Ocean Deep Convection

Abstract It is argued that non-hydrostatic effects are important in the dynamics of open-ocean deep convection on horizontal scales ~ 1 km, typical of sinking plumes. The formulation and numerical implementation of a non-hydrostatic ocean model appropriate for the explicit representation of plume-scale dynamics is described. The model is used to study the spin-up, through convective overturning induced by surface cooling, and subsequent geostrophic adjustment of a baroclinic vortex with a horizontal scale of the order of the Rossby radius of deformation.

A mechanistic model of grass root growth and development dependent upon photosynthesis and nitrogen uptake

A mechanistic partitioning model of grass root growth and vertical extension is developed. The root is divided into a series of horizontal sections, and each section is assumed to absorb soil nitrogen independently of the others. The carbon substrate required by the root is acquired by downgradient diffusion from the shoot compartment, which is the site of photosynthesis. Water conditions are assumed to be non-limiting, and structural growth is dependent upon the concentration of carbon and nitrogen substrates. New root structure is placed in a pool of mobile material which may be absorbed by the fixed root or diffused to adjacent layers. Downward diffusion of this pool from the lowest root section results in root extension into uncolonized soil. Maintenance, senescence, nitrogen recycling from senescencing material, root ruboff and exudation are included in the model. The model is used to simulate the growth of grass shoots and roots in response to a seasonally varying environment and different soil nitrogen concentrations.

Equatorial Kelvin waves as revealed by EOS Microwave Limb Sounder observations and European Centre for Medium-Range Weather Forecasts analyses: Evidence for slow Kelvin waves of zonal wave number 3

[1] Temperature and ozone observations from the Microwave Limb Sounder (MLS) on the EOS Aura satellite are used to study equatorial wave activity in the autumn of 2005. In contrast to previous observations for the same season in other years, the temperature anomalies in the middle and lower tropical stratosphere are found to be characterized by a strong wave-like eastward progression with zonal wave number equal to 3. Extended empirical orthogonal function (EOF) analysis reveals that the wave 3 components detected in the temperature anomalies correspond to a slow Kelvin wave with a period of 8 days and a phase speed of 19 m/s. Fluctuations associated with this Kelvin wave mode are also apparent in ozone profiles. Moreover, as expected by linear theory, the ozone fluctuations observed in the lower stratosphere are in phase with the temperature perturbations, and peak around 20-30 hPa where the mean ozone mixing ratios have the steepest vertical gradient. A search for other Kelvin wave modes has also been made using both the MLS observations and the analyses from one experiment where MLS ozone profiles are assimilated into the European Centre for Medium-Range Weather Forecasts (ECMWF) data assimilation system via a 6-hourly 3D var scheme. Our results show that the characteristics of the wave activity detected in the ECMWF temperature and ozone analyses are in good agreement with MLS data.

Evaluation of ozone total column measurements by the Ozone Monitoring Instrument using a data assimilation system

[1] On 15 July 2004, the Ozone Monitoring Instrument (OMI) on board the EOS Aura mission was launched. One of OMI’s priorities is to continue the record of high spatial resolution ozone total column measurements provided by the various Total Ozone Mapping Spectrometer (TOMS) instruments since 1978. To this end, it is essential to estimate the errors affecting OMI ozone total column measurements and to see whether the actual accuracy is consistent with estimated values before launch. In this paper, data assimilation techniques are used to create a large comparison data set composed of ozone analyses resulting from assimilation of standard meteorological observations and ozone retrievals (independent of OMI measurements) into a numerical weather prediction model. This data setprovidesexcellentglobalcoverageandtemporalresolution,notlimitedbythespatialand temporal distribution of other satellite or ground based information. The accuracy of the analyses is evaluated against ozone total column retrievals from Brewer measurements, while the assimilated ozone data set is compared to ozone predictions made using the ECMWF model, to check for the presence of bias. The OMI ozone column measurements considered here are obtained with the TOMS-V8 total ozone algorithm and denoted as OMTO3 columns. They are compared with simulated OMI ozone columns, i.e., the quantities that the TOMS-V8 algorithm would retrieve in the case when the atmospheric ozone profile at a specific location and time is equal to the one prescribed by the analysis. In this way, the comparison is statistically robust even when data acquired during a relatively short temporal interval or over a relatively small geographical area only is considered. A discussion of relevant error sources (including systematic components), vertical resolution, and contributions from prior information is provided. Special attention is given to determining the importance of representativeness errors. Our results show a solar zenith angle (SZA) dependence of the bias between measured and simulated OMI columns. This is believed to be due to moderate nonlinearity of the observation forward model and its effects on our definition of simulated OMI columns at high SZA. In view of these findings the final results of the intercomparison methodology used in this paper are obtained from OMI ozone columns retrieved using the basic implementation of the TOMS-V8 algorithm applied to measurements taken at SZA not exceeding 70. Intercomparison results between measured and simulated OMI ozone columns at SZA less than 70 show a relative bias of � 3.2 ± 3.1% and a root-mean-square error of 4.5 ± 1.5%. The resulting bias is consistent with available estimates of the bias ofOMTO3columnswithrespecttoSBUV/2between60Sand60N,aswellaswithrespect to global Dobson data and Brewer measurements between 30N and 60N.

The GlobMODEL Demonstrator: Assimilation of New Satellite Products in an Operational Meteorological Center

As part of its Data User Element programme, the European Space Agency funded the GlobMODEL project which aimed at investigating the scientific, technical, and organizational issues associated with the use and exploitation of remotely-sensed observations, particularly from new sounders. A pilot study was performed as a ldquodemonstratorrdquo of the GlobMODEL idea, based on the use of new data, with a strong European heritage, not yet assimilated operationally. Two parallel assimilation experiments were performed, using either total column ozone or ozone profiles retrieved at the Royal Netherlands Meteorological Institute (KNMI) from the Ozone Monitoring Instrument (OMI). In both cases, the impact of assimilating OMI data in addition to the total ozone columns from the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) on the European Centre for Medium Range Weather Forecasts (ECMWF) ozone analyses was assessed by means of independent measurements. We found that the impact of OMI total columns is mainly limited to the region between 20 and 80 hPa, and is particularly important at high latitudes in the Southern hemisphere where the stratospheric ozone transport and chemical depletion are generally difficult to model with accuracy. Furthermore, the assimilation experiments carried out in this work suggest that OMI DOAS (Differential Optical Absorption Spectroscopy) total ozone columns are on average larger than SCIAMACHY total columns by up to 3 DU, while OMI total columns derived from OMI ozone profiles are on average about 8 DU larger than SCIAMACHY total columns. At the same time, the demonstrator brought to light a number of issues related to the assimilation of atmospheric composition profiles, such as the shortcomings arising when the vertical resolution of the instrument is not properly accounted for in the assimilation. The GlobMODEL demonstrator accelerated scientific and operational utilization of new observations and its results prompted ECMWF to start the operational assimilation of OMI total column ozone data.

The UGAMP use and diagnosis of the ECMWF meteorological analyses

The UGAMP uses The ECMWF analyses to produce atmospheric diagnostics which are of use to atmospheric and ocean scientists. Here, we explain the motivation behind the work and describe the datasets with special reference to the spatial grids and data format. The choice of these is limited by current hardware and software requirements. We discuss computer requirements and forecast future requirements. Finally, we discuss problems with the approach.