A fully coupled regional climate system model (CNRM-RCSM4) has been used over the Mediterranean region to investigate the direct and semi-direct effects of aerosols, but also their role in the radiation-atmosphereocean interactions through multi-annual ensemble simulations (2003)(2004)(2005)(2006)(2007)(2008)(2009)) with and without aerosols and oceanatmosphere coupling. Aerosols have been taken into account in CNRM-RCSM4 through realistic interannual monthly AOD climatologies. An evaluation of the model has been achieved, against various observations for meteorological parameters, and has shown the ability of CNRM-RCSM4 to reproduce the main patterns of the Mediterranean climate despite some biases in sea surface temperature (SST), radiation and cloud cover. The results concerning the aerosol radiative effects show a negative surface forcing on average because of the absorption and scattering of the incident radiation. The SW surface direct effect is on average -20.9 Wm -2 over the Mediterranean Sea, -14.7 Wm -2 over Europe and -19.7 Wm -2 over northern Africa. The LW surface direct effect is weaker as only dust aerosols contribute (?4.8 Wm -2 over northern Africa). This direct effect is partly counterbalanced by a positive semi-direct radiative effect over the Mediterranean Sea (?5.7 Wm -2 on average) and Europe (?5.0 Wm -2 ) due to changes in cloud cover and atmospheric circulation. The total aerosol effect is consequently negative at the surface and responsible for a decrease in land (on average -0.4°C over Europe, and -0.5°C over northern Africa) and sea surface temperature (on average -0.5°C for the Mediterranean SST). In addition, the latent heat loss is shown to be weaker (-11.0 Wm -2 ) in the presence of aerosols, resulting in a decrease in specific humidity in the lower troposphere, and a reduction in cloud cover and precipitation. Simulations also indicate that dust aerosols warm the troposphere by absorbing solar radiation, and prevent radiation from reaching the surface, thus stabilizing the troposphere. The comparison with the model response in atmosphere-only simulations shows that these feedbacks are attenuated if SST cannot be modified by aerosols, highlighting the importance of using coupled regional models over the Mediterranean. Oceanic convection is also strengthened by aerosols, which tends to reinforce the Mediterranean thermohaline circulation. In parallel, two case studies are presented to illustrate positive feedbacks between dust aerosols and regional climate. First, the eastern Mediterranean was subject to high dust aerosol loads in June 2007 which reduce land and sea surface temperature, as well as air-sea humidity fluxes. Because of northern wind over the eastern Mediterranean, drier and cooler air has been consequently advected from the sea to the African continent, reinforcing the direct dust effect over land. On the contrary, during the western European heat wave in June 2006, dust aerosols have contributed to reinforcing an important ridge responsible for dry and 123Cl...

This study is an analysis of the seasonal all‐sky surface solar radiation variability in Europe during 1970–2000 using surface observations from the Global Energy Balance Archive (GEBA). On the basis of the annual means period 1970–1985, there is a statistically significant decline of −3.0% decade−1 (−3.8 Wm−2 decade−1) followed by a nonsignificant rise of 0.3% decade−1 (0.4 Wm−2 decade−1) during 1985–2000. The behavior of the solar radiation for spring is similar to the annual series and has the strongest increase of 1.6% decade−1 (2.5 Wm−2 decade−1) during 1985–2000. In summer a similar evolution to the annual and spring time series is shown but has a stronger decline of −3.2% decade−1 (−6.8 Wm−2 decade−1) during 1970–1985. A small positive nonsignificant trend is reported for the winter means time series while a statistically significant negative trend of −2.5% decade−1 (−2.1 Wm−2 decade−1) was found in autumn during 1970–2000. By comparing variations in all‐sky solar radiation with changes in cloud cover and NAO, we attribute the winter and autumn trends mainly to the NAO through the modification of mid‐to‐low cloud cover in southern Europe and the spring and summer trends to mid‐to‐low cloud cover in northern Europe. However, because the cloud cover and solar radiation relationship weakens in the low‐frequency variability, it suggests that other effects such as aerosols may also play a role. In addition, aerosols could be interfering with the relationship between solar radiation and NAO, contributing to a strengthening of their correlation in the low‐frequency variability during winter and autumn.

[1] The surface solar radiation (SSR) is an important factor influencing the local and global energy budget. However, information on the spatial and temporal variation of SSR is limited. A more commonly available measure, which may provide such information, is the diurnal temperature range (DTR). In this study we analyze the relationship between DTR and SSR in Europe between 1970 and 2005 on seasonal and decadal scale. When comparing the mean anomalies time series composed of 31 pairs of sites with long-term SSR and DTR measurements, we found a correlation coefficient of 0.87 in the annual mean and between 0.61 and 0.92 in the seasonal mean anomalies. When investigating the individual pairs of SSR and DTR individually, we found that local correlations are mostly lower than the European mean and that they decrease rapidly in seasons and latitudes with low incident angles and at high alpine altitude. The highest correlation on local and seasonal scales seems to be connected with the variability of the large-scale circulation in Europe. The output of 11 simulations of current generation regional climate models over Europe confirms the strong relationship between SSR and DTR. The seasonal dependence of the relationship is well reproduced, but the absolute values of DTR and SSR are mostly too low. The pattern of decrease (dimming) and increase (brightening) in SSR and DTR was not reproduced in the modeled time series. There is still strong evidence from both models and observations that DTR is a reliable representative of SSR.Citation: Makowski, K., E. B. Jaeger, M. Chiacchio, M. Wild, T. Ewen, and A. Ohmura (2009), On the relationship between diurnal temperature range and surface solar radiation in Europe,

Tropical cyclones (TCs) can have devastating socioeconomic impacts. Understanding the nature and causes of their variability is of paramount importance for society. However, historical records of TCs are too short to fully characterize such changes and paleosediment archives of Holocene TC activity are temporally and geographically sparse. Thus, it is of interest to apply physical modeling to understanding TC variability under different climate conditions. Here we investigate global TC activity during a warm climate state (mid-Holocene, 6,000 yBP) characterized by increased boreal summer insolation, a vegetated Sahara, and reduced dust emissions. We analyze a set of sensitivity experiments in which not only solar insolation changes are varied but also vegetation and dust concentrations. Our results show that the greening of the Sahara and reduced dust loadings lead to more favorable conditions for tropical cyclone development compared with the orbital forcing alone. In particular, the strengthening of the West African Monsoon induced by the Sahara greening triggers a change in atmospheric circulation that affects the entire tropics. Furthermore, whereas previous studies suggest lower TC activity despite stronger summer insolation and warmer sea surface temperature in the Northern Hemisphere, accounting for the Sahara greening and reduced dust concentrations leads instead to an increase of TC activity in both hemispheres, particularly over the Caribbean basin and East Coast of North America. Our study highlights the importance of regional changes in land cover and dust concentrations in affecting the potential intensity and genesis of past TCs and suggests that both factors may have appreciable influence on TC activity in a future warmer climate.hurricanes | mid-Holocene | dust emissions | vegetation changes | land cover changes