Tropospheric and stratospheric aspects of the North Atlantic Oscillation: An eddy perspective

Recent studies have described the leading patterns of variability of the Northern Hemisphere extratropical circulation as an annular structure. The associated sea-level winter feature resembles the North Atlantic Oscillation pattern; however, it has been noticed that its centers of action, covering most of the Arctic, have a more zonally symmetric structure. This mode has been referred as the Arctic Oscillation (AO). By considering the vertical structure of the AO, some authors have suggested that a stratosphere-troposphere interaction mechanism may be the source of the interannual variability associated with the AO and, therefore, it could have some relevances also for the NAO. Thus, the NAO and the AO may be considered as different facets of the same phenomenon. In the present paper we analyze the interannual variability of 52 Northern hemisphere winters in the NCEP reanalysis. The study rests on a principal component analysis and singular value decomposition of the sea level pressure, the geopotential heights at 500 hPa and 50 hPa and the zonal wind at 200 hPa. Moreover, following Rossby earlier works, we compute the principal components also for the eddy fields. The analysis performed suggests that the eddy patterns of variability allow a better identification of the modes connected to the NAO in the middle troposphere and in the lower stratosphere. Two distinct stratospheric wave patterns are found to be related to NAO and PNA modes. The covariance analysis suggests a dynamical link with the Atlantic jet exit for the former mode, and a connection with the Atlantic jet entrance for the latter mode. In view of the NAO-AO debate, the results here presented seem to confirm that the NAO and PNA mechanisms contribute separately to the atmospheric eddies variability in the troposphere and in the lower stratosphere

Olive agroecosystems in the Mediterranean Basin: multitrophic analysis of climate effects with process-based representation of soil water balance

Olive is of major eco-social importance for the Mediterranean Basin, a climate change and biodiversity hotspot of global relevance where remarkable climate change is expected over the next few decades with unknown ecosystem impacts. However, climate impact assessments on terrestrial ecosystems have long been constrained by a narrow methodological basis (ecological niche models, ENMs) that is correlative and hence largely omits key impact drivers such as trophic interactions and the effect of water availability, the latter being especially relevant to desertification-prone Mediterranean ecosystems. ENMs use correlative measures of water availability unsuitable for making projections about the future. To bridge this gap, mechanistic approaches such as physiologically-based weather- driven demographic models (PBDMs) may be used as they embed by design both the biology of trophic interactions and a mechanistic representation of soil water balance. Here we report progress towards assessing climate effects on olive culture across the Mediterranean region using mechanistic PBDMs that project regionally the multitrophic population dynamics of olive and olive fly as affected by daily weather and soil water balance

Med-CORDEX initiative for Mediterranean climate studies

The Mediterranean is expected to be one of the most prominent and vulnerable climate change "hotspots" of the twenty-first century, and the physical mechanisms underlying this finding are still not clear. Furthermore, complex interactions and feedbacks involving ocean-atmosphere-land-biogeochemical processes play a prominent role in modulating the climate and environment of the Mediterranean region on a range of spatial and temporal scales. Therefore, it is critical to provide robust climate change information for use in vulnerability-impact-adaptation assessment studies considering the Mediterranean as a fully coupled environmental system. The Mediterranean Coordinated Regional Downscaling Experiment (Med-CORDEX) initiative aims at coordinating the Mediterranean climate modeling community toward the development of fully coupled regional climate simulations, improving all relevant components of the system from atmosphere and ocean dynamics to land surface, hydrology, and biogeochemical processes. The primary goals of Med-CORDEX are to improve understanding of past climate variability and trends and to provide more accurate and reliable future projections, assessing in a quantitative and robust way the added value of using high-resolution and coupled regional climate models. The coordination activities and the scientific outcomes of Med-CORDEX can produce an important framework to foster the development of regional Earth system models in several key regions worldwide. ©2016 American Meteorological Society