To take into account the strong nonlinearities of vertical fluxes due to small-scale heterogeneities of surface properties, more and more coupled general circulation models compute part of their ...atmospheric physical parameterizations, either the surface fluxes or the whole package, on the finer grid of their ocean or land model. A modification of a traditional interpolation scheme is presented to calculate the values of atmospheric variables over surface model grid points. In addition to the desirable properties of flux conservation and preservation of a constant field, the new scheme allows discontinuities in the interpolated fields at the surface model's boundaries and orographic jumps, while remaining continuous elsewhere. It can also be tuned separately for each variable. The modified scheme is then evaluated using the circulation model of the Laboratoire de Meteorologie Dynamique coupled to the Laboratoire d'Oceanographie Dynamique et de Climatologie tropical Pacific Ocean model using the delocalized physics method. The results show a large improvement of heat and humidity fluxes near the focus region of the South American coast in the southeastern equatorial Pacific, and a subsequent westward propagation of significant cold SST anomalies.
The Antarctic ice sheet (AIS) is sensitive to short-term extreme meteorological events that can leave long-term impacts on the continent's surface mass balance (SMB). We investigate the impacts of ...atmospheric rivers (ARs) on the AIS precipitation budget using an AR detection algorithm and a regional climate model (Modèle Atmosphérique Régional) from 1980 to 2018. While ARs and their associated extreme vapor transport are relatively rare events over Antarctic coastal regions (∼3 days per year), they have a significant impact on the precipitation climatology. ARs are responsible for at least 10% of total accumulated snowfall across East Antarctica (localized areas reaching 20%) and a majority of extreme precipitation events. Trends in AR annual frequency since 1980 are observed across parts of AIS, most notably an increasing trend in Dronning Maud Land; however, interannual variability in AR frequency is much larger. This AR behavior appears to drive a significant portion of annual snowfall trends across East Antarctica, while controlling the interannual variability of precipitation across most of the AIS. AR landfalls are most likely when the circumpolar jet is highly amplified during blocking conditions in the Southern Ocean. There is a fingerprint of the Southern Annular Mode (SAM) on AR variability in West Antarctica with SAM+ (SAM−) favoring increased AR frequency in the Antarctic Peninsula (Amundsen-Ross Sea coastline). Given the relatively large influence ARs have on precipitation across the continent, it is advantageous for future studies of moisture transport to Antarctica to consider an AR framework especially when considering future SMB changes.
Mid-latitude westerlies are a major component of the atmospheric circulation and understanding their behaviour under climate change is important for understanding changes in precipitation, storms and ...atmosphere-ocean momentum, heat and CO2 exchanges. The Southern Hemisphere westerlies, have been particularly studied in terms of the latter aspects, since the Southern Ocean is a key region for the global oceanic circulation as well as for CO2 uptake. In this study, we analyse, mainly in terms of maximum jet-stream position, the behaviour of the southern westerlies for the Last Glacial Maximum (LGM, 21 000 yr ago, which is the last past cold extreme) and for a future climate, obtained after stabilisation of the RCP4.5 scenario (hereafter RCP). The a priori guess would be that the behaviour of the westerly jet-stream would be similar when examining its changes from LGM to pre-industrial (PI) conditions and from PI to RCP, i.e. in both cases a poleward shift in response to global warming. We show that this is in fact not the case, due to the impact of altitude changes of the Antarctic ice-sheet and/or to sea-ice cover changes.
The search for rocky exoplanets plays an important role in our quest for extra-terrestrial life. Here, we discuss the extreme physical properties possible for the first characterized rocky ...super-Earth, CoRoT-7b (R_pl = 1.58 \pm 0.10 R_Earth, Mpl = 6.9 \pm 1.2 M_Earth). It is extremely close to its star (a = 0.0171 AU = 4.48 R_st), with its spin and orbital rotation likely synchronized. The comparison of its location in the (Mpl, Rpl) plane with the predictions of planetary models for different compositions points to an Earth-like composition, even if the error bars of the measured quantities and the partial degeneracy of the models prevent a definitive conclusion. The proximity to its star provides an additional constraint on the model. It implies a high extreme-UV flux and particle wind, and the corresponding efficient erosion of the planetary atmosphere especially for volatile species including water. Consequently, we make the working hypothesis that the planet is rocky with no volatiles in its atmosphere, and derive the physical properties that result. As a consequence, the atmosphere is made of rocky vapours with a very low pressure (P \leq 1.5 Pa), no cloud can be sustained, and no thermalisation of the planetary is expected. The dayside is very hot (2474 \leq 71 K at the sub-stellar point) while the nightside is very cold (50 to 75 K). The sub-stellar point is as hot as the tungsten filament of an incandescent bulb, resulting in the melting and distillation of silicate rocks and the formation of a lava ocean. These possible features of CoRoT-7b could be common to many small and hot planets, including the recently discovered Kepler-10b. They define a new class of objects that we propose to name "Lava-ocean planets".
The Preliminary VOCALS Model Assessment (PreVOCA) aims to assess contemporary atmospheric modeling of the subtropical South East Pacific, with a particular focus on the clouds and the marine boundary ...layer (MBL). Models results from fourteen modeling centers were collected including operational forecast models, regional models, and global climate models for the month of October 2006. Forecast models and global climate models produced daily forecasts, while most regional models were run continuously during the study period, initialized and forced at the boundaries with global model analyses. Results are compared in the region from 40° S to the equator and from 110° W to 70° W, corresponding to the Pacific coast of South America. Mean-monthly model surface winds agree well with QuikSCAT observed winds and models agree fairly well on mean weak large-scale subsidence in the region next to the coast. However they have greatly differing mean geographic patterns of cloud fraction with only a few models agreeing well with MODIS observations. Most models also underestimate the MBL depth by several hundred meters in the eastern part of the study region. The diurnal cycle of liquid water path is underestimated by most models at the 85° W 20° S stratus buoy site compared with satellite, consistent with previous modeling studies. The low cloud fraction is also underestimated during all parts of the diurnal cycle compared to surface-based climatologies. Most models qualitatively capture the MBL deepening around 15 October 2006 at the stratus buoy, associated with colder air at 700 hPa.
Stable carbon isotope analyses have shown that South African australopiths did not have exclusively frugivorous diets, but also consumed significant quantities of C
4 foods such as grasses, sedges, ...or animals that ate these foods. Yet, these studies have had significant limitations. For example, hominin sample sizes were relatively small, leading some to question the veracity of the claim for australopith C
4 consumption. In addition, it has been difficult to determine which C
4 resources were actually utilized, which is at least partially due to a lack of stable isotope data on some purported australopith foods. Here we begin to address these lacunae by presenting carbon isotope data for 14 new hominin specimens, as well as for two potential C
4 foods (termites and sedges). The new data confirm that non-C
3 foods were heavily utilized by australopiths, making up about 40% and 35% of
Australopithecus and
Paranthropus diets respectively. Most termites in the savanna-woodland biome of the Kruger National Park, South Africa, have intermediate carbon isotope compositions indicating mixed C
3/C
4 diets. Only 28% of the sedges in Kruger were C
4, and few if any had well-developed rhizomes and tubers that make some sedges attractive foods. We conclude that although termites and sedges might have contributed to the C
4 signal in South African australopiths, other C
4 foods were also important. Lastly, we suggest that the consumption of C
4 foods is a fundamental hominin trait that, along with bipedalism, allowed australopiths to pioneer increasingly open and seasonal environments.
Dental microwear texture (DMT) analysis is commonly applied for dietary reconstruction of vertebrates. The temporal scale on which dietarily informative microscopic wear forms on enamel surfaces is ...crucial to infer dietary flexibility and seasonality. Microwear is assumed to form shortly before the individual's death, reflecting information pertaining to the last meals consumed (“last supper” effect). In primate feeding experiments, microwear features formed within hours, suggesting rates of turnover within one to two weeks. As DMT formation experiments testing the persistence of microwear three-dimensionally (textures) are still lacking, we test how quickly DMTs form and pre-existing ones are overwritten in a terminal feeding experiment with 72 rats. In two groups of 36, rats received either a standard pelleted diet or the same pelleted diet containing 4% loess, an aeolian, silt-sized sediment, for 24 consecutive days. Then 6 individuals from each group were sacrificed, while the rest (n = 30) were switched to the diet they had not received before. On day 1, 2, 4, 8, 16, and 24 after the diet switch, 5 of the remaining individuals were sacrificed, creating a cohort of n = 5 each for each time point. We applied DMT analysis on first and second upper molars. For upper second molars, rats show a subsequent change in DMT after the switch, with visible differences from day 2 on. On upper first molars, microwear textures were variable for individuals sacrificed directly after the initial 24-day feeding period, thus obscuring significant differences in diet-induced dental wear. We find turnover faster and more pronounced when switching from loess-containing to standard pellet as compared to the opposite switch. The trend for either decreasing or increasing parameter values after the diet switch approaches a plateau between 16 and 24 days for many DMT parameters, suggesting that, under these experimental conditions, the “last supper” effect needs at least two weeks to overwrite previous DMT patterns.
•Turnover time of DMT is tested on two experimental diets.•Subsequent change in DMT parameters is observed after switch on new diet.•Between 16 and 24 days after switch, previous diet signal is overprinted.•No immediate “last supper” effect visible, turnover needs at least two weeks.
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