The ECMWF re-analysis project is a meteorological reanalysis project.The first reanalysis product, ERA-15, generated re-analyses for approximately 15 years, from December 1978 to February 1994. The second product, ERA-40 begins in 1957 and covers 45 years to 2002. As a precursor to a revised extended reanalysis product to replace ERA-40, ECMWF has recently released ERA-Interim, which covers the period from 1979 to present.In addition to re-analysing all the old data using a consistent system, the reanalyses also make use of much archived data that was not available to the original analyses. This allows for the correction of many historical hand-drawn maps where the estimation of features was common in areas of data sparsity. The ability is also present to create new maps of atmosphere levels that were not commonly used until more recent times. Wikipedia.
Journal of Geophysical Research: Oceans | Year: 2012
Ocean waves play an important role in processes that govern the fluxes across the air-sea interface and in the upper-ocean mixing. Equations for current and heat are presented that include effects of ocean waves on the evolution of the properties of the upper ocean circulation and heat budget. The turbulent transport is modeled by means of the level-21/2 Mellor-Yamada scheme, which includes an equation for the production and destruction of Turbulent Kinetic Energy (TKE). The TKE equation in this work includes production due to wave breaking, production due to wave-induced turbulence and/or Langmuir turbulence, effects of buoyancy and turbulent dissipation. As a first test, the model is applied to the simulation of the daily cycle in SST at one location in the Arabian sea for the period of October 1994 until October 1995. For this location, the layer where the turbulent mixing occurs, sometimes called the Turbocline, is only a few meters thick and fairly thin layers are needed to give a proper representation of the diurnal cycle. The dominant processes that control the diurnal cycle turn out to be buoyancy production and turbulent production by wave breaking, while in the deeper layers of the ocean the Stokes-Coriolis force plays an important role. © 2012. American Geophysical Union. All Rights Reserved.
Journal of Geophysical Research: Atmospheres | Year: 2011
The sensitivity of European Centre for Medium-Range Weather Forecasts (ECMWF) numerical weather prediction analyses to the empirical refractivity coefficients used to assimilate bending angles derived from GPS radio occultation measurements has been investigated. We have compared the Smith and Weintraub (1953) coefficients with the "best average" values proposed by Reger (2002). The Reger values produce simulated bending angles in the upper troposphere and stratosphere that are larger by ∼0.115%. This produces a cooling in the troposphere by around ∼-0.1 K, which improves the fit to radiosonde geopotential height measurements in the Northern Hemisphere but degrades the fit in the tropics and Southern Hemisphere. The cooling is caused primarily by Reger's increase in the "k1" refractivity coefficient, which accounts for the dry air contribution to the total refractivity. It is confirmed that this cooling can be reduced by introducing nonideal gas effects in the hydrostatic integration of the forward model. However, the Reger k1 coefficient should also be adjusted to k 1 = 77.643 K hPa-1 if it is used in a forward model that includes nonideal gas effects when evaluating the refractivity from the model state. Furthermore, if the nonideal gas effects are introduced in a consistent way, we find that the Reger coefficients plus nonideal gas effects produce very similar results to the Smith and Weintraub values, where nonideal gas effects are neglected. © 2011 by the American Geophysical Union.
Joly M.,Meteo - France |
Atmospheric Environment | Year: 2012
The observation sites that make up air quality monitoring networks can have very different characteristics (topography, climatology, distance to emission sources, etc), which are partially described in the meta-information provided with data sets. At the scale of Europe, the description of the sites depends on the institute(s) in charge of the air quality monitoring in each country, and is based on specific criteria that can be sometimes rather subjective. The purpose of this study is to build an objective, homogeneous, and pollutant-specific classification of European air quality monitoring sites, primarily for the purpose of model verification and chemical data assimilation. Most studies that tackled this issue so far were based on limited data sets, and often took into account additional external data such as population density, emission estimates, or land cover maps. The present study demonstrates the feasibility of a classification only based on the past time series of measured pollutants. The underlying idea is that the true fingerprint of a given monitoring site lies within its past observation values. On each site to be categorized, eight indicators are defined to characterize each pollutant time series (O 3, NO 2, NO, SO 2, or PM 10) of the European AirBase and the French BDQA (Base de Données de Qualité de l'Air) reference sets of validated data over the period 2002-2009. A Linear Discriminant Analysis is used to best discriminate the rural and urban sites. After projection on the Fisher axis, ten classes are finally determined on the basis of fixed thresholds, for each molecule. The method is validated by cross-validation and by direct comparison with the existing meta-data. The link between the classes obtained and the meta-data is strongest with NO, NO 2, and PM 10. Across Europe, the classification exhibits interesting large-scale features: some contrasts between different regions depend on the pollutant considered. Comparing the classes obtained for different pollutants at the same site reveals an interesting consistency between the separate classifications. The robustness of the method is finally assessed by comparing the classifications obtained for two distinct subsets of years. The robustness - and thus the skill of the objective classification - is satisfying for all of the species, and is highest with NO and NO 2. © 2011 Elsevier Ltd.
Quarterly Journal of the Royal Meteorological Society | Year: 2014
The impact of Radio Occultation observations from Global Positioning System satellites (GPSRO) on global Numerical Weather Prediction (NWP) has been analysed with a recent version of the European Centre for Medium-range Weather Forecasting (ECMWF) Integrated Forecasting System. As in previous studies, the use of GPSRO was found to improve the NWP forecast skill and to drastically decrease model-induced temperature biases in the analysis. The maximum forecast impact is in the lower and middle stratosphere, where the GPSRO observations have the smallest errors, but it is also visible in the troposphere. The tropospheric impact of GPSRO comes in part from direct tropospheric measurements and in part from stratosphere-troposphere interactions: this second mechanism is found to be particularly important during the Northern Hemisphere winter. The forecast impact of GPSRO observations is compared with that of conventional and hyperspectral satellite nadir sounders. It is found that although GPSRO data have a smaller impact than those of either class of nadir sounders, they are still able to account for a considerable fraction (30-70%) of the global forecast error reduction afforded by the use of the full observing system over a system that uses only conventional observations. When forecast verification is performed against radiosonde observations, GPSRO is found to be the most valuable satellite observing system in the lower stratosphere. This is remarkable in view of the relative sparseness of the GPSRO spatial and temporal coverage and an indication of the potential improvements that a denser GPSRO observing network would be able to provide. The forecast impact of GPSRO observations is also evaluated in the context of a data denial assimilation experiment with respect to the full observing system. Results are found to be consistent with those from the reduced baseline observational network and also indicate a statistically significant positive impact on tropospheric synoptic skill scores. © 2013 Royal Meteorological Society.
Gleisner H.,Danish Meteorological Institute |
Atmospheric Measurement Techniques | Year: 2013
The possibility of simplifying the retrieval scheme required to produce GNSS radio occultation refractivity climatologies is investigated. In a new, simplified retrieval approach, the main statistical analysis is performed in bending angle space and an estimate of the average bending angle profile is then propagated through an Abel transform. The average is composed of means and medians of ionospheric corrected bending angles up to 80 km. Above that, the observed profile is exponentially extrapolated to infinity using a fixed a priori scale height. The new approach circumvents the need to introduce a "statistical optimisation" processing step in which individual bending angle profiles are merged with a priori data, often taken from a climatology. This processing step can be complex, difficult to interpret, and is generally recognised as a potential source of structural uncertainty. The new scheme is compared with the more conventional approach of averaging individual refractivity profiles, produced with the implementation of statistical optimisation used in the EUMETSAT Radio Occultation Meteorology Satellite Application Facility (ROM SAF) operational processing. It is shown that the two GNSS radio occultation climatologies agree to within 0.1% from 5 km up to 35-40 km, for the three months January, February, and March 2011. During this time period, the new approach also produces slightly better agreement with ECMWF analyses between 40-50 km, which is encouraging. The possible limitations of the new approach caused by mean residual ionospheric errors and low observation numbers are discussed briefly, and areas for future work are suggested. © Author(s) 2013.