The ERA5 global reanalysis

A new version of the general circulation model CNRM-CM has been developed jointly by CNRM-GAME (Centre National de Recherches Meteorologiques—Groupe d’etudes de l’Atmosphere Meteorologique) and Cerfacs (Centre Europeen de Recherche et de Formation Avancee) in order to contribute to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The purpose of the study is to describe its main features and to provide a preliminary assessment of its mean climatology. CNRM-CM5.1 includes the atmospheric model ARPEGE-Climat (v5.2), the ocean model NEMO (v3.2), the land surface scheme ISBA and the sea ice model GELATO (v5) coupled through the OASIS (v3) system. The main improvements since CMIP3 are the following. Horizontal resolution has been increased both in the atmosphere (from 2.8° to 1.4°) and in the ocean (from 2° to 1°). The dynamical core of the atmospheric component has been revised. A new radiation scheme has been introduced and the treatments of tropospheric and stratospheric aerosols have been improved. Particular care has been devoted to ensure mass/water conservation in the atmospheric component. The land surface scheme ISBA has been externalised from the atmospheric model through the SURFEX platform and includes new developments such as a parameterization of sub-grid hydrology, a new freezing scheme and a new bulk parameterisation for ocean surface fluxes. The ocean model is based on the state-of-the-art version of NEMO, which has greatly progressed since the OPA8.0 version used in the CMIP3 version of CNRM-CM. Finally, the coupling between the different components through OASIS has also received a particular attention to avoid energy loss and spurious drifts. These developments generally lead to a more realistic representation of the mean recent climate and to a reduction of drifts in a preindustrial integration. The large-scale dynamics is generally improved both in the atmosphere and in the ocean, and the bias in mean surface temperature is clearly reduced. However, some flaws remain such as significant precipitation and radiative biases in many regions, or a pronounced drift in three dimensional salinity.

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The CNRM-CM5.1 global climate model: description and basic evaluation

[1] We present version 4 of the Met Office Hadley Centre “EN” series of data sets of global quality controlled ocean temperature and salinity profiles and monthly objective analyses, which covers the period 1900 to present. We briefly describe the EN4 data sources, processing, quality control procedures, and the method of generating the analyses. In particular, we highlight improvements relative to previous versions, which include a new duplicate profile removal procedure and the inclusion of three new quality control checks. We discuss in detail a novel method for providing uncertainty estimates for the objective analyses and improving the background error variance estimates used by the analysis system. These were calculated using an iterative method that is relatively robust to initial misspecification of background error variances. We also show how the method can be used to identify issues with the analyses such as those caused by misspecification of error variances and demonstrate the impact of changes in the observing system on the uncertainty in the analyses.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2013JC009067

EN4: Quality controlled ocean temperature and salinity profiles and monthly objective analyses with uncertainty estimates

The Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) system

A new operational ocean reanalysis system (ORAS4) has been implemented at ECMWF. It spans the period 1958 to the present. This article describes its main components and evaluates its quality. The adequacy of ORAS4 for the initialization of seasonal forecasts is discussed, along with the robustness of some prominent climate signals.

ORAS4 has been evaluated using different metrics, including comparison with observed ocean currents, RAPID-derived transports, sea-level gauges, and GRACE-derived bottom pressure. Compared to a control ocean model simulation, ORAS4 improves the fit to observations, the interannual variability, and seasonal forecast skill. Some problems have been identified, such as the underestimation of meridional overturning at 26°N, the magnitude of which is shown to be sensitive to the treatment of the coastal observations.

ORAS4 shows a clear and robust shallowing trend of the Pacific Equatorial thermocline. It also shows a clear and robust nonlinear trend in the 0–700 m ocean heat content, consistent with other observational estimates. Some aspects of these climate signals are sensitive to the choice of sea-surface temperature product and the specification of the observation-error variances. The global sea-level trend is consistent with the altimeter estimate, but the partition into volume and mass variations is more debatable, as inferred by discrepancies in the trend between ORAS4- and GRACE-derived bottom pressure.

/pdf/evaluation-of-the-ecmwf-ocean-reanalysis-system-oras4-1g4fx79wf2.pdf

Evaluation of the ECMWF ocean reanalysis system ORAS4

Quality control of ocean temperature and salinity profiles — Historical and real-time data

Global assimilation of air temperature, humidity, wind and pressure from surface stations

Ship and buoy reports of wind, air pressure, temperature, humidity, and sea temperature for 2007 and 2008 have been compared with values from the operational Met Office global numerical weather prediction (NWP) system. Ship reports have been categorized by vessel type, recruiting country, and manual or automatic reporting. Most estimated ship winds (except Dutch ones) are too strong and are better treated as measured winds. After height adjustment, the average ship wind speeds are reasonably consistent with buoy wind speeds, but the global model winds are 6%–12% weaker. Extra care is needed when comparing/assimilating values close to the coast. Ship air temperatures are too warm during the afternoon due to solar heating of the ship. Adjustment of the pressure to sea level is a problem for some larger ships. Passenger ship reports are relatively poor quality for several variables and their winds are rather strong. Automated ship reports and those from research and coast guard vessels tend to be of...

Factors Affecting Ship and Buoy Data Quality: A Data Assimilation Perspective

Some real-time radiosonde reports are now available with higher vertical resolution and higher precision than the alphanumeric TEMP code. There are also extra metadata; for example, the software version may indicate whether humidity corrections have been applied at the station. Numerical weather prediction (NWP) centers and other users need to start using the new Binary Universal Form for Representation of Meteorological Data (BUFR) reports because the alphanumeric codes are being withdrawn. TEMP code has various restrictions and complexities introduced when telecommunication speed and costs were overriding concerns; one consequence is minor temperature rounding errors. In some ways BUFR reports are simpler: the whole ascent should be contained in a single report. BUFR reports can also include the time and location of each level; an ascent takes about 2 h and the balloon can drift 100 km or more laterally. This modernization is the largest and most complex change to the worldwide reporting of radi...

Bruce Ingleby

Papers

Quality control of ocean temperature and salinity profiles — Historical and real-time data

Global assimilation of air temperature, humidity, wind and pressure from surface stations

Factors Affecting Ship and Buoy Data Quality: A Data Assimilation Perspective

Progress toward High-Resolution, Real-Time Radiosonde Reports

The 2005/06 winter in Europe and the United Kingdom:Part 1 –How the Met Office forecast was produced and communicated