On the Impact of the Assimilation of SARAL/AltiKa Wave Data in the Operational Wave Model MFWAM

As a part of our calibration/validation activities five months of SARAL/AltiKa wave data have been analyzed in this study. A robust quality control procedure using threshold values on signal and retrieved wave heights was implemented before the assimilation. Assimilation runs in the wave model Météo-France (MFWAM) were performed for a long period. The validation of the model outputs was performed with independent wave observations from altimeter and buoy data. The results indicate good performance in terms of bias and scatter index for the significant wave height and the peak wave period. Statistical analyses were performed for different ocean basins (high and intermediate latitudes and tropics). The use of SARAL/AltiKa and Jason-2 wave data combined was also investigated. This leads to further improvements for the analysis and forecast periods. In other respects, the impact of the assimilation of SARAL/AltiKa wave data is discussed for waves under strong wind conditions such as typhoons Fitow and Danas which occurred in early October 2013.     

Reconstruction of the Sunspot Number Source Database and the 1947 Zurich Discontinuity

Solar Physics - The final version (V.19) of the total solar irradiance data from the SOlar Radiation and Climate Experiment (SORCE) Total Irradiance Monitor has been released. This version includes...     

Depletion of Column Ozone in the Arctic During the Winters of 1993-94 and 1994-95

The total ozone reduction in the Arctic during the winters of 1993/94 and 1994/95 has been evaluated using the ground-based total ozone measurements of five SAOZ spectrometers distributed in the Arctic and from number density profiles of a balloon-borne version of the instrument. The ozone change resulting from transport has been removed using a 3D Chemistry Transport Model (CTM) run without chemistry. A cumulative total ozone depletion at the end of winter in March of 18% ± 4% in 1994 and of 32% ± 4% in 1995 was observed within the polar vortex, and of 15% ± 4% in both years outside the vortex. This evaluation is not sensitive to the vertical transport in the model. The periods, locations and altitudes at which ozone loss occurred were tightly connected to temperatures lower than NAT condensation temperature. The maximum loss was observed at 50 hPa in 1994 and lower, 60-80 hPa, in 1995. Half of the depletion in 1994 and three quarters in 1995 occurred during the early winter, showing that a late final warming is not a prerequisite for large ozone destruction in the northern hemisphere. The timing, the geographical location and the altitude of the ozone losses are well captured by the 3D CTM photochemical model using current chemistry, but its amplitude at low sun during the early winter, is underestimated. The model simulations also capture the early season reductions observed outside the vortex. This suggests that the losses occurred in situ in the early winter, when low temperatures are frequent, and not later in March, when ozone is most reduced inside the vortex, which would be the case if leakage from the vortex was the cause of the depletion.     

High swell warnings in the Caribbean Islands during March 2008

Long and high swells are dangerous for many islands located in the Tropics because they can generate large breakers and long run up associated with large set up when reaching the coast. Most of the time those islands do not experience large waves especially in usually protected areas, for instance, by coral reefs or wind protected. Long waves have the ability to reach such areas, thanks to wave set up, shoaling and bottom refraction. This article describes an example of such high swell events and its impact on the islands. The buoy network used by the French National Weather Service and all available satellite observations related to waves are presented together with numerical sea-state models used to issue early warnings.     

Low CO2 concentrations in the Gulf of Guinea during the upwelling season in 2006

The fugacity of CO₂ (fCO₂) was measured underway from 27 May to 5 July 2006 in the Gulf of Guinea when the upwelling conditions were taking place. The equatorial and the coastal upwellings are responsible for the large CO₂ outgassing observed in the tropical Atlantic. The highest fCO₂ (655 μatm) was measured in the eastern coastal upwelling. However, area of low fCO₂ are also observed. Those occurred north of 2°N, in the Guinea Current, and near 6°S close to the coast due to the Congo River discharge. The decrease of salinity is a major factor explaining low fCO₂. In the South Equatorial Counter Current region, south of 6°S near 10°W, low fCO₂ are not related to a salinity effect as this region is subject to excess evaporation. A comparison with the meridional transects of the RMS St Helena made in 1995–1996 near 15°W suggests that these low fCO₂ or even slight undersaturations can be observed from about 4°S to 10°S. It seems that they occur mainly in boreal summer. They could be caused by transport of water that has been in contact with the atmosphere long enough to come close to equilibrium. The low fCO₂ area are not reproduced by the CO₂ climatology probably because of the coarse resolution and the lack of data in this region. Despite the low fCO₂ area observed in 2006, the ΔfCO₂ in 2006 is higher than the 1995 climatology for the region 10°S–2°N, 10°W–10°E suggesting that fCO₂ is increasing over time but from the few cruises available, it is difficult to definitely conclude.     

The O2 nightglow in the martian atmosphere by SPICAM onboard of Mars-Express

We present observations of the O₂(a¹Δ_g) nightglow at 1.27 μm on Mars using the SPICAM IR spectrometer onboard of the Mars Express orbiter. In contrast to the O₂(a¹Δ_g) dayglow that results from the ozone photodissociation, the O₂(a¹Δ_g) nightglow is a product of the recombination of O atoms formed by CO₂ photolysis on the dayside at altitudes higher than 80 km and transported downward above the winter pole by the Hadley circulation. The first detections of the O₂(a¹Δ_g) nightglow in 2010 indicate that it is about two order of magnitude less intense than the dayglow (Bertaux, J.-L., Gondet, B., Bibring, J.-P., Montmessin, F., Lefèvre, F. [2010]. Bull. Am. Astron. Soc. 42, 1040; Clancy et al. [2010]. Bull. Am. Astron. Soc. 42, 1041). SPICAM IR sounds the martian atmosphere in the near-IR range (1–1.7 μm) with the spectral resolution of 3.5 cm^?1 in nadir, limb and solar occultation modes. In 2010 the vertical profiles of the O₂(a¹Δ_g) nightside emission have been obtained near the South Pole at latitudes of 82–83°S for two sequences of observations: L_s = 111–120° and L_s = 152–165°. The altitude of the emission maximum varied from 45 km on L_s = 111–120° to 38–49 km on L_s = 152–165°. Averaged vertically integrated intensity of the emission at these latitudes has shown an increase from 0.22 to 0.35 MR. Those values of total vertical emission rate are consistent with the OMEGA observations on Mars-Express in 2010. The estimated density of oxygen atoms at altitudes from 50 to 65 km varies from 1.5 × 10¹¹ to 2.5 × 10¹¹ cm^?3. Comparison with the LMD general circulation model with photochemistry (Lefèvre, F., Lebonnois, S., Montmessin, F., Forget, F. [2004]. J. Geophys. Res. 109, E07004; Lefèvre et al. [2008]. Nature 454, 971–975) shows that the model reproduces fairly well the O₂(a¹Δ_g) emission layer observed by SPICAM when the large field of view (>20 km on the limb) of the instrument is taken into account.