Oceanic control of decadal North Atlantic sea level pressure variability in winter

The predictability of winter‐time North Atlantic sea level pressure (SLP) variability has been investigated by means of an ensemble of integrations with an atmospheric general circulation model (AGCM) forced by observed sea surface temperatures (SSTs) for the period 1951–1994. The results imply that the SLP variations on timescales of several years to decades may be predictable, provided the SST anomalies themselves used to drive the AGCM can be predicted. The model, however, suffers from systematic errors, and the simulated centers of action are shifted relative to those observed

Impacts of variations in Caspian Sea surface area on catchment-scale and large-scale climate

The Caspian Sea (CS) is the largest inland lake in the world. Large variations in sea level and surface area occurred in the past and are projected for the future. The potential impacts on regional and large-scale hydroclimate are not well understood. Here, we examine the impact of CS area on climate within its catchment and across the northern hemisphere, for the first time with a fully coupled climate model. The Community Earth System Model (CESM1.2.2) is used to simulate the climate of four scenarios: (1) larger than present CS area, (2) current area, (3) smaller than present area, and (4) no-CS scenario. The results reveal large changes in the regional atmospheric water budget. Evaporation (E) over the sea increases with increasing area, while precipitation (P) increases over the south-west CS with increasing area. P-E over the CS catchment decreases as CS surface area increases, indicating a dominant negative lake-evaporation feedback. A larger CS reduces summer surface air temperatures and increases winter temperatures. The impacts extend eastwards, where summer precipitation is enhanced over central Asia and the north-western Pacific experiences warming with reduced winter sea ice. Our results also indicate weakening of the 500-hPa troughs over the northern Pacific with larger CS area. We find a thermal response triggers a southward shift of the upper troposphere jet stream during summer. Our findings establish that changing CS area results in climate impacts of such scope that CS area variations should be incorporated into climate model simulations, including palaeo and future scenarios. Plain Language Summary The Caspian Sea is the largest land-locked water body in the world. It is filled by rivers draining a vast region from northern Russia to Iran. The size of the Caspian Sea has varied considerably over recent centuries and millennia due to various factors, including changes in climate. Conversely, as the area of the sea changes it also has impacts on the climate, but there are significant questions about how and where those impacts would be felt. In this study we used a state-of-the-art climate model in which we specified different sizes of Caspian Sea in order to examine how the climate changes as its area increases. We observed that the local seasonal cycle of temperatures gets smaller, and evaporation increases, while there are more spatially complex changes in local rainfall. Furthermore, the impacts on atmospheric circulation occur as far as the north Pacific, with resulting increases in temperature and decreases in sea-ice coverage in winter as the Caspian area increases. The climate impacts are so significant and geographically extensive that climate models used to simulate climate change (both in future and past scenarios) should incorporate changes to the Caspian Sea area if they are to robustly model regional climate

Identification of regulatory variants associated with genetic susceptibility to meningococcal disease.

Non-coding genetic variants play an important role in driving susceptibility to complex diseases but their characterization remains challenging. Here, we employed a novel approach to interrogate the genetic risk of such polymorphisms in a more systematic way by targeting specific regulatory regions relevant for the phenotype studied. We applied this method to meningococcal disease susceptibility, using the DNA binding pattern of RELA - a NF-kB subunit, master regulator of the response to infection - under bacterial stimuli in nasopharyngeal epithelial cells. We designed a custom panel to cover these RELA binding sites and used it for targeted sequencing in cases and controls. Variant calling and association analysis were performed followed by validation of candidate polymorphisms by genotyping in three independent cohorts. We identified two new polymorphisms, rs4823231 and rs11913168, showing signs of association with meningococcal disease susceptibility. In addition, using our genomic data as well as publicly available resources, we found evidences for these SNPs to have potential regulatory effects on ATXN10 and LIF genes respectively. The variants and related candidate genes are relevant for infectious diseases and may have important contribution for meningococcal disease pathology. Finally, we described a novel genetic association approach that could be applied to other phenotypes

Validation of the hydrological cycle of ERA 40

The European Centre for Medium-Range Weather Forecasts (ECMWF) has prepared a new 40 year reanalysis dataset (ERA40). Based on the observational data that were used, the whole ERA40 time period 1958-2001 can be divided into three parts: the satellite period 1989-2001 when a large amount of satellite data were assimilated into the ERA40 system, the pre-satellite period 1958-1972 when no satellite data were available, and the transition period 1973-1988 when the amount of satellite data that were assimilated increases with time. These three periods correspond also to the three streams which were produced separately during the ERA40 production timeframe. The ERA40 dataset is expected to be a major dataset for climate research. Within the ERA40 project, the MPI (Max Planck Institute for Meteorology) had the task to perform a validation of the hydrological cycle. Here, mainly the 6 hour forecasts were considered. The validation shows that the ERA40 hydrological cycle has changed in several respects compared to the previous ERA15 re-analysis. The hydrological cycle over land is generally improved compared to ERA15. These improvements comprise the eliminated cold biases in winter, the reduced occurrence of negative P-E (precipitation minus evapotranspiration) values, the removed dry bias in winter over Europe, and an improved representation of the snowpack. But the ERA40 hydrological cycle also has several deficiencies. The largest problem is the fact that the global water budget is not only unbalanced, but also P-E over the ocean is positive (and not negative as it should be) in the long term mean for the satellite and transition periods. This is related to an overestimation of precipitation over the ocean, especially in the tropics. The evapotranspiration over land is overestimated for many catchments, and, thus, the corresponding P-E is often underestimated. Using a simplified land surface scheme it was possible to derive improved values of evapotranspiration and runoff from ERA40 precipitation and 2m temperature that are consistent with the ERA40 data. The quality of the hydrological cycle differs between the periods as the biases in the hydrological cycle are strongly influenced by the different observing systems available in the three periods. Therefore, conclusions drawn for hydrological trends should be taken with great care

Climate simulations and pollen data reveal the distribution and connectivity of temperate tree populations in eastern Asia during the Last Glacial Maximum

Publications on temperate deciduous tree refugia in Europe are abundant, but little is known about the patterns of temperate tree refugia in eastern Asia, an area where biodiversity survived Quaternary glaciations and which has the world's most diverse temperate flora. Our goal is to compare climate model simulations with pollen data in order to establish the location of glacial refugia during the Last Glacial Maximum (LGM). Limits in which temperate deciduous trees can survive are taken from the literature. The model outputs are first tested for the present by comparing climate models with published modern pollen data. As this method turned out to be satisfactory for the present, the same approach was used for the LGM. Climate model simulations (ECHAM5 T106), statistically further downscaled, are used to infer the temperate deciduous tree distribution during the LGM. These were compared with available fossil temperate tree pollen occurrences. The impact of the LGM on the eastern Asian climate was much weaker than on the European climate. The area of possible tree growth shifts only by about 2∘ to the south between the present and the LGM. This contributes to explaining the greater biodiversity of forests in eastern Asia compared to Europe. Climate simulations and the available, although fractional, fossil pollen data agree. Therefore, climate estimations can safely be used to fill areas without pollen data by mapping potential refugia distributions. The results show two important areas with population connectivity: the Yellow Sea emerged shelf and the southern Himalayas. These two areas were suitable for temperate deciduous tree growth, providing corridors for population migration and connectivity (i.e. less population fragmentation) in glacial periods. Many tree populations live in interglacial refugia, not glacial ones. The fact that the model simulation for the LGM fits so well with observed pollen distribution is another indication that the model used is good enough to also simulate the LGM period

On the connection between the 1984 Atlantic warm event and the 1982-1983 ENSO

The warm event which spread in the tropical Atlantic during Spring-Summer 1984 is assumed to be partially initiated by atmospheric disturbances, themselves related to the major 1982–1983 El-Niño which occurred 1 year earlier in the Pacific. This paper tests such an hypothesis. For that purpose, an atmospheric general circulation model (AGCM) is forced by different conditions of climatic and observed sea surface temperature and an Atlantic ocean general circulation model (OGCM) is subsequently forced by the outputs of the AGCM. It is firstly shown that both the AGCM and the OGCM correctly behave when globally observed SST are used: the strengthening of the trades over the tropical Atlantic during 1983 and their subsequent weakening at the beginning of 1984 are well captured by the AGCM, and so is the Spring 1984 deepening of the thermocline in the eastern equatorial Atlantic, simulated by the OGCM. As assumed, the SST anomalies located in the El-Niño Pacific area are partly responsible for wind signal anomaly in the tropical Atlantic. Though this remotely forced atmospheric signal has a small amplitude, it can generate, in the OGCM run, an anomalous sub-surface signal leading to a flattening of the thermocline in the equatorial Atlantic. This forced oceanic experiment cannot explain the amplitude and phase of the observed sub-surface oceanic anomaly: part of the Atlantic ocean response, due to local interaction between ocean and atmosphere, requires a coupled approach. Nevertheless this experiment showed that anomalous conditions in the Pacific during 82–83 created favorable conditions for anomaly development in the Atlantic