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51.
52.
Intrinsic variability (IV) in regional climate models (RCMs) is often assumed to be small because at climatological timescales, the model solutions tend to be dominated by the model??s lateral boundary conditions. Recent studies have indicated that this IV may actually be large in certain instances for some variables. Direct interpretation of anomalies from RCM sensitivity studies relies on the assumption that differences between model simulations are entirely due to a physical forcing. However, if IV is as large or larger than the physical signal, then this assumption is violated. Using a 20 member ensemble of RCM simulations, we verify that IV of precipitation within a RCM can be large enough to violate the sensitivity study assumption, and we show that generating ensembles of simulations can help reduce the level of IV. We also present two indicators that can rule out the influence of IV when it is ambiguous whether anomalies within a sensitivity study are due to the sensitivity perturbation or whether they are due to IV. 相似文献
53.
Tommy G. Jensen Timothy J. Campbell Richard A. Allard Richard Justin Small Travis A. Smith 《Ocean Dynamics》2011,61(5):657-674
The coupled ocean atmosphere mesoscale prediction system that includes the Navy Coastal Ocean Model has been configured for
the Kuroshio Extension region using multiple one-way nested high-resolution grids. The coupled model system was used to simulate
a strong cold-air outbreak event from 31 Jan to 7 Feb 2005 in good agreement with meteorological data from a surface buoy
data and QuikSCAT scatterometer winds. Latent heat fluxes and sensible heat fluxes were computed during the event with daily
averages in excess of 1,500 W/m2 and 500 W/m2, respectively, and combined instantaneous turbulent heat fluxes up to 2,300 W/m2. The largest heat fluxes were found in two large meanders of the Kuroshio and along its southern flank. Strong gradients
in turbulent heat fluxes coincided with strong sea surface temperature gradients and were maintained during the cold-air outbreak
simulation. The large turbulent heat fluxes lead to significant subtropical mode water formation during the event at a rate
about 10 Sv in the cyclonic recirculation region south of the Kuroshio. This increased the volume of core layer mode water
within the temperature range 16°C to 18°C by 10% and increased the surface area of that layer directly exposed to the atmosphere
by a factor close to 5 in the model domain. 相似文献
54.
Global warming is expected to affect both the frequency and severity of extreme weather events, though projections of the response of these events to climate warming remain highly uncertain. The range of changes reported in the climate modelling literature is very large, sometimes leading to contradictory results for a given extreme weather event. Much of this uncertainty stems from the incomplete understanding of the physics of extreme weather processes, the lack of representation of mesoscale processes in coarse-resolution climate models, and the effect of natural climate variability at multi-decadal time scales. However, some of the spread in results originates simply from the variety of scenarios for future climate change used to drive climate model simulations, which hampers the ability to make generalizations about predicted changes in extreme weather events. In this study, we present a meta-analysis of the literature on projected future extreme weather events in order to quantify expected changes in weather extremes as a function of a common metric of global mean temperature increases. We find that many extreme weather events are likely to be significantly affected by global warming. In particular, our analysis indicates that the overall frequency of global tropical cyclones could decrease with global warming but that the intensity of these storms, as well as the frequency of the most intense cyclones could increase, particularly in the northwestern Pacific basin. We also found increases in the intensity of South Asian monsoonal rainfall, the frequency of global heavy precipitation events, the number of North American severe thunderstorm days, North American drought conditions, and European heatwaves, with rising global mean temperatures. In addition, the periodicity of the El Niño–Southern Oscillation may decrease, which could, in itself, influence extreme weather frequency in many areas of the climate system. 相似文献
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Timothy A. Kral Travis S. Altheide Adrienne E. Lueders Andrew C. Schuerger 《Planetary and Space Science》2011,59(2-3):264-270
Conditions on the surface of Mars would appear to be too hostile for life as we know it. But the subsurface is another matter. If liquid water is present, even intermittently, life forms present would at least be protected from the lethal radiation bombarding the surface. However, life would have to contend with variations in pressure and possibly extended periods of desiccation. The research reported here involves both active metabolism (methanogenesis) at 400 and 50 mbar of pressure, pressures that would be found in the near subsurface of Mars, and survival following desiccation at both 1 bar (a pressure that would be found in the Martian subsurface) and 6 mbar (the lowest pressure at the surface and very near subsurface). The three methanogens tested for active metabolism, Methanothermobacter wolfeii, Methanosarcina barkeri and Methanobacterium formicicum, all demonstrated methane production at both 400 and 50 mbar on JSC Mars-1, a Mars soil simulant. Methane production at 50 mbar was much reduced compared to that at 400 mbar, most likely due to the greater stress at the lower pressure. In desiccation survival experiments, M. barkeri had survived 330 days of desiccation at 1 bar, while M. wolfeii and M. formicicum survived 180 and 120 days, respectively. Methanococcus maripaludis did not survive desiccation at all at 1 bar. At 6 mbar, M. wolfeii, M. barkeri and M. formicicum survived 120 days of desiccation while M. maripaludis survived 60 days. These results along with results from previous research would seem to indicate that there is no reason that methanogens could not inhabit the subsurface of Mars. 相似文献
57.
Travis?J.?TennerEmail author Marc?M.?Hirschmann Anthony?C.?Withers Paola?Ardia 《Contributions to Mineralogy and Petrology》2012,163(2):297-316
The onset of hydrous partial melting in the mantle above the transition zone is dictated by the H2O storage capacity of peridotite, which is defined as the maximum concentration that the solid assemblage can store at P and T without stabilizing a hydrous fluid or melt. H2O storage capacities of minerals in simple systems do not adequately constrain the peridotite water storage capacity because
simpler systems do not account for enhanced hydrous melt stability and reduced H2O activity facilitated by the additional components of multiply saturated peridotite. In this study, we determine peridotite-saturated
olivine and pyroxene water storage capacities at 10–13 GPa and 1,350–1,450°C by employing layered experiments, in which the
bottom ~2/3 of the capsule consists of hydrated KLB-1 oxide analog peridotite and the top ~1/3 of the capsule is a nearly
monomineralic layer of hydrated Mg# 89.6 olivine. This method facilitates the growth of ~200-μm olivine crystals, as well
as accessory low-Ca pyroxenes up to ~50 μm in diameter. The presence of small amounts of hydrous melt ensures that crystalline
phases have maximal H2O contents possible, while in equilibrium with the full peridotite assemblage (melt + ol + pyx + gt). At 12 GPa, olivine and
pyroxene water storage capacities decrease from ~1,000 to 650 ppm, and ~1,400 to 1,100 ppm, respectively, as temperature increases
from 1,350 to 1,450°C. Combining our results with those from a companion study at 5–8 GPa (Ardia et al., in prep.) at 1,450°C,
the olivine water storage capacity increases linearly with increasing pressure and is defined by the relation
C\textH2 \textO\textolivine ( \textppm ) = 57.6( ±16 ) ×P( \textGPa ) - 169( ±18 ). C_{{{\text{H}}_{2} {\text{O}}}}^{\text{olivine}} \left( {\text{ppm}} \right) = 57.6\left( { \pm 16} \right) \times P\left( {\text{GPa}} \right) - 169\left( { \pm 18} \right). Adjustment of this trend for small increases in temperature along the mantle geotherm, combined with experimental determinations
of
D\textH2 \textO\textpyx/olivine D_{{{\text{H}}_{2} {\text{O}}}}^{\text{pyx/olivine}} from this study and estimates of
D\textH2 \textO\textgt/\textolivine D_{{{\text{H}}_{2} {\text{O}}}}^{{{\text{gt}}/{\text{olivine}}}} , allows for estimation of peridotite H2O storage capacity, which is 440 ± 200 ppm at 400 km. This suggests that MORB source upper mantle, which contains 50–200 ppm
bulk H2O, is not wet enough to incite a global melt layer above the 410-km discontinuity. However, OIB source mantle and residues
of subducted slabs, which contain 300–1,000 ppm bulk H2O, can exceed the peridotite H2O storage capacity and incite localized hydrous partial melting in the deep upper mantle. Experimentally determined values
of
D\textH2 \textO\textpyx/\textolivine D_{{{\text{H}}_{2} {\text{O}}}}^{{{\text{pyx}}/{\text{olivine}}}} at 10–13 GPa have a narrow range of 1.35 ± 0.13, meaning that olivine is probably the most important host of H2O in the deep upper mantle. The increase in hydration of olivine with depth in the upper mantle may have significant influence
on viscosity and other transport properties. 相似文献
58.
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60.
Reproductive aspects of life history are known to be important in recovery following disturbance in many plant species although
this has not been well studied in mangroves. Hurricane Charley devastated large areas of mangroves in Charlotte Harbor, Florida,
in August 2004. We surveyed 6 forests in Charlotte Harbor (2002, 2003, and 2005) and 16 in Tampa Bay, Florida (2001, 2002,
2003, and 2005) for total numbers of reproducing trees and trees heterozygotic for albinism that produce both normal and albino
propagules. Tree size (estimated height and diameter at breast height) was also recorded for sentinel heterozygotic trees.
Total number of reproducing trees km−1 was used as an index of reproductive output of the population, and deviation from the 3∶1 (normal:albino propagules) ratio
on heterozygotic trees expected with 100% selfing was used to estimate outcrossing. Numbers ofRhizophora mangle reproducing trees km−1 of shoreline in Charlotte Harbor were reduced by an order of magnitude following Hurricane Charley, while numbers of reproducing
trees in Tampa Bay were similar to those of previous years. Reduced reproduction in Charlotte Harbor was accompanied by fewer
new recruits in plots on Sanibel and Captiva Islands. Numbers of new recruits after the storm also tended to be fewer in plots
where canopy loss was greater. More new recruits occurred in sites that had higher densities of pre-stormRhizophora seedlings and greater relative dominance byRhizophora. Outcrossing of sentinel trees was 2.5 times greater, in Charlotte Harbor (mean site−1=33.6±6.7%; with 17% of forest sites completely selfing) than in Tampa Bay (mean site−1=13.4±4.7%; with 40% of sites completely selfing), although the implications for seedling recruitment of this difference are
not known. 相似文献