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1.
High resolution simulations of January and July climate over the western Alpine region with a nested Regional Modeling system 总被引：1，自引：0，他引：1
M. R. Marinucci F. Giorgi M. Beniston M. Wild P. Tschuck A. Ohmura A. Bernasconi 《Theoretical and Applied Climatology》1995,51(3):119-138
Summary High resolution January and July present day climatologies over the central-western Alpine region are simulated with a Regional Climate Model (RegCM) nested within a General Circulation Model (GCM). The RegCM was developed at the National Center for Atmospheric Research (NCAR) and is run at 20 km grid point spacing. The model is driven by output from a present day climate simulation performed with the GCM ECHAM3 of the Max Planck Institute for Meteorology (MPI) at T106 resolution (~ 120 km). Five January and July simulations are conducted with the nested RegCM and the results for surface air temperature and precipitation are compared with a gridded observed dataset and a dataset from 99 observing stations throughout the Swiss territory. The driving ECHAM3 simulation reproduces well the position of the northeastern Atlantic jet, but underestimates the jet intensity over the Mediterranean. Precipitation over the Alpine region in the ECHAM3 simulation is close to observed in January but lower than observed in July. Compared to the driving GCM, the nested RegCM produces more precipitation in both seasons, mostly as a result of the stronger model orographic forcing. Average RegCM temperature over the Swiss region is 2–3 degrees higher than observed, while average precipitation is within 30% of observed values. The spatial distribution of precipitation is in general agreement with available gridded observations and the model reproduces the observed elevation dependency of precipitation in the summer. In the winter the simulated elevation of maximum precipitation amounts is lower than observed. Precipitation frequencies are overestimated, while precipitation intensities show a reasonable agreement with observations, especially in the winter. Sensitivity experiments with different cumulus parameterizations, soil moisture initialization and model topography are discussed. Overall, the model performance at the high resolution used here did not deteriorate compared to previous lower resolution experiments.The National Center for Atmospheric Research is sponsored by the National Science Foundation.With 11 Figures 相似文献
2.
Takeshi Ohmura Takeo Moriya Chengshi Piao Takaya Iwasaki Toshikastu Yoshi Shin'ichi Sakai Tetsuya Takeda Kaoru Miyashita Humihito Yamazaki Kiyoshi Ito Akira Yamazaki Yoji Shimada Katsuya Tashiro Hiroki Miyamachi 《Island Arc》2001,10(3-4):215-227
Abstract The 1995 Kobe (Hyogo-ken Nanbu) earthquake (MJMA 7.2, Mw 6.9) occurred on Jan. 17, 1995, at a depth of 17 km, beneath the areas of southern part of Hyogo prefecture and Awaji Island. To investigate P-wave velocity distribution and seismological characteristics in the aftershock area of this great earthquake, a wide-angle and refraction seismic exploration was carried out by the Research Group for Explosion Seismology (RGES) . The profile including 6 shot points and 205 observations was 135 km in length, extending from Keihoku, Northern Kyoto prefecture, through Kobe, to Seidan on Awaji Island. The charge of each shot was 350–700 kg. The P-wave velocity structure model showed a complicated sedimentary layer which is shallower than 2.5 km, a 2.5 km-thick basement layer whose velocity is 5.5 km/s, overlying the crystalline upper crust, and the boundary between the upper and lower crust.
Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and some aftershock clusters were situated deeper than the boundary between the upper and lower crust. We found that the P-velocity in the upper crust beneath the northern part of Awaji Island is 5.64 km/s which is 3% lower than that of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed. 相似文献
Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and some aftershock clusters were situated deeper than the boundary between the upper and lower crust. We found that the P-velocity in the upper crust beneath the northern part of Awaji Island is 5.64 km/s which is 3% lower than that of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed. 相似文献
3.
Atsumu Ohmura 《GeoJournal》1984,8(3):221-228
Seasonal change in the energy balance on the arctic tundra is presented. The thermal stability of a dry snow cover is investigated in detail. In addition to high reflection by the snow cover, a significant absorption of solar radiation on the very surface of the snow cover was found responsible for the thermal stability. The efficient absorption of solar radiation by the surface rather than the interior of the snow cover and the almost immediate removal of the absorbed energy through radiative emission and turbulent heat fluxes keep the temperature of the snow cover low.The energy balances for the melt and postmelt period for various arctic surfaces are compared. The most important difference of the energy balance between the tundra and tther low attitude arctic surface, such as the sea and ablation areas of glaciers, is not the net radiation but the latent heat of fusion. Extremely small heat cosuumption through the melt on the tundra is the basis for higher temperature, characteristics to the tundra climate in the Arctic. 相似文献
4.
Present status and variations in the Arctic energy balance 总被引：1，自引：1，他引：0
Atsumu Ohmura 《Polar Science》2012,6(1):5-13
The total solar irradiance (TSI, or solar constant) acquired a new value: 1361 W m?2 instead of 1365 W m?2. However a long-term variation of TSI was not detected. The solar irradiance at the earth's surface is considerably smaller (170 W m?2) than previously believed (e.g. 198 W m?2 of IPCC AR4). The previous overestimation is due to the underestimation of the absorption of solar radiation in the atmosphere. The absorption of solar radiation in the atmosphere at about 90 W m?2, or 25–28% of the primary solar radiation from space. The global mean atmospheric downward terrestrial radiation is much larger (345 W m?2) than previously assumed (325 W m?2 of IPCC AR4). The Arctic has regions of negative annual net radiation, a very rare phenomenon on the globe. These regions are the Central Arctic Ocean with its multi-year ice coverage and the accumulation area of the Greenland ice sheet. The energy balance of these regions is presented. Long-wave incoming radiation has been increasing in the Arctic at a rate of 4–5 W m?2/Decade. The Greenland ice sheet exhibits a large vertical difference in net radiation from the ablation area to the dry snow zone in summer. It ranges from 80 W m?2 in the ablation area to 20 W m?2 at the equilibrium line and to 10 W m?2 in the dry snow zone. This gradient determines the melt gradient on the ice sheet, and is mainly caused by the altitude variation in atmospheric long-wave radiation, seconded by the albedo variation. The effect of albedo in summer for various surfaces is discussed. Simulation capabilities of radiation for many GCMs are investigated. 相似文献
5.
Snow cover fraction (SCF) has a significant influence on the surface albedo and thus on the radiation balance and surface
climate. Long-term three dimensional simulations with general circulation models (GCMs) show that the SCF greatly affects
the climate in the Northern Hemisphere. By means of both ground observations and remotely sensed data, several deficiencies
in the SCF simulated by the current ECHAM4 GCM were identified: over mountainous areas a substantial overestimation in the
SCF was found whereas flat areas showed a distinctly underestimated SCF. This work proposes a new parametrization of the SCF
for use in GCMs. Evaluations illustrate that it is beneficial to distinguish between the following three terrains: (1) flat,
non-forested areas, (2) mountainous regions and (3) forests. The modified SCF parametrization for flat, non-forested areas
was derived by using global datasets of ground-based snow depth and remote sensing observations of snow cover data. A 3-dimensional
ECHAM4 simulation showed that this modification raises the SCF by up to approximately 20%, mainly in areas with a relatively
thin snow cover. The comparison between remotely sensed and simulated mean monthly surface albedo revealed a significant overestimation
of the surface albedo in snow-covered mountainous areas. An extension of the current SCF parametrization in ECHAM4 to take
into account mountain effects, based on the French climate model Arpège, yielded a close agreement with satellite-derived
surface albedo. The adoption of the submodel for snow albedo, as used in the Canadian Land Surface Scheme (CLASS), combined
with a newly developed simple snow interception model, demonstrated the ability to capture the main physical processes of
snow-covered canopies, including the albedo. The validation of the new parametrization with Boreal Ecosystem-Atmosphere Study
(BOREAS) field data showed that the modification is appropriate to capture the main features of the albedo over snow-covered
forests during and after heavy snowfall events. Furthermore, the proposed modification has a beneficial impact on the delayed
snow melt in spring, a well-known problem in many current GCMs: The simulated surface albedo over the boreal forests decreases
by approximately 0.1 during winter and spring, which is in better agreement with ground-based observations. This induces a
significant rise in the surface temperature over extended parts of Eurasia and North America in late spring, which subsequently
yields a faster snowmelt and an accelerated retreat of the snow line.
Received: 28 April 2000 / Accepted: 18 December 2000 相似文献
6.
The disposition of radiative energy in the global climate system: GCM-calculated versus observational estimates 总被引：1，自引：1，他引：0
M. Wild A. Ohmura H. Gilgen E. Roeckner M. Giorgetta J.-J. Morcrette 《Climate Dynamics》1998,14(12):853-869
A comprehensive dataset of direct observations is used to assess the representation of surface and atmospheric radiation
budgets in general circulation models (GCMs). Based on combined measurements of surface and collocated top-of-the-atmosphere
fluxes at more than 700 sites, a lack of absorption of solar radiation within the atmosphere is identified in the ECHAM3 GCM,
indicating that the shortwave atmospheric absorption calculated in the current generation of GCMs, typically between 60 and
70 Wm-2, is too low by 10–20 Wm-2. The surface and atmospheric radiation budgets of a new version of the Max-Planck Institute GCM, the ECHAM4, differ considerably
from other GCMs in both short- and longwave ranges. The amount of solar radiation absorbed in the atmosphere (90 Wm-2) is substantially larger than typically found in current GCMs, resulting in a lower absorption at the surface (147 Wm-2). It is shown that this revised disposition of solar energy within the climate system generally reduces the biases compared
to the observational estimates of surface and atmospheric absorption. The enhanced shortwave absorption in the ECHAM4 atmosphere
is due to an increase in both simulated clear-sky and cloud absorption compared to ECHAM3. The increased absorption in the
cloud-free atmosphere is related to an enhanced absorption of water vapor, and is supported in stand-alone comparisons of
the radiation scheme with synchronous observations. The increased cloud absorption, on the other hand, is shown to be predominantly
spurious due to the coarse spectral resolution of the ECHAM4 radiation code, thus providing no physical explanation for the
“anomalous cloud absorption” phenomenon. Quantitatively, however, an additional increase of atmospheric absorption due to
clouds as in ECHAM4 is, at least at low latitudes, not in conflict with the observational estimates, though this does not
rule out the possibility that other effects, such as highly absorbing aerosols, could equally contribute to close the gap
between models and observations. At higher latitudes, however, the increased cloud absorption is not supported by the observational
dataset. Overall, this study points out that not only the clouds, but also the cloud-free atmosphere might be responsible
for the discrepancies between observational and simulated estimates of shortwave atmospheric absorption. The smaller absorption
of solar radiation at the surface in ECHAM4 is compensated by an increased downward longwave flux (344 Wm-2), which is larger than in other GCMs. The enhanced downward longwave flux is supported by surface measurements and by a stand-alone
validation of the radiation scheme for clear-sky conditions. The enhanced flux also ensures that a sufficient amount of energy
is available at the surface to maintain a realistic intensity of the global hydrological cycle. In contrast, a one-handed
revision of only the shortwave radiation budget to account for the increased shortwave absorption in GCM atmospheres may induce
a global hydrological cycle that is too weak.
Received: 26 February 1998 / Accepted: 18 May 1998 相似文献
7.
Annual precipitation,evaporation,and calculated accumulation from reanalysis model outputs have been investigated for the Greenland Ice Sheet (GrIS),based on the common period of 1989-2001.The ERA-40 and ERA-interim reanalysis data showed better agreement with observations than do NCEP-1 and NCEP-2 reanalyses.Further,ERA-interim showed the closest spatial distribution of accumulation to the observation.Concerning temporal variations,ERA-interim showed the best correlation with precipitation observations at five synoptic stations,and the best correlation with in situ measurements of accumulation at nine ice core sites.The mean annual precipitation averaged over the whole GrIS from ERA-interim (363 mm yr 1) and mean annual accumulation (319 mm yr 1) are very close to the observations.The validation of accumulation calculated from reanalysis data against ice-core measurements suggests that further improvements to reanalysis models are needed. 相似文献
8.
Atsumu Ohmura Dr. 《GeoJournal》1984,8(2):221-228
Seasonal change in the energy balance on the arctic tundra is presented. The thermal stability of a dry snow cover is investigated in detail. In addition to high reflection by the snow cover, a significant absorption of solar radiation on the very surface of the snow cover was found responsible for the thermal stability. The efficient absorption of solar radiation by the surface rather than the interior of the snow cover and the almost immediate removal of the absorbed energy through radiative emission and turbulent heat fluxes keep the temperature of the snow cover low. The energy balances for the melt and postmelt period for various arctic surfaces are compared. The most important difference of the energy balance between the tundra and tther low attitude arctic surface, such as the sea and ablation areas of glaciers, is not the net radiation but the latent heat of fusion. Extremely small heat cosuumption through the melt on the tundra is the basis for higher temperature, characteristics to the tundra climate in the Arctic. 相似文献
9.
The ability of a high resolution (T106) version of the ECHAM3 general circulation model to simulate regional scale surface radiative fluxes has been assessed using observations from a new compilation of worldwide instrumentally-measured surface fluxes (Global Energy Balance Archive, GEBA). The focus is on the European region where the highest density of observations is found, and their use for the validation of global and regional climate models is demonstrated. The available data allow a separate assessment of the simulated fluxes of surface shortwave, longwave, and net radiation for this region. In summer, the incoming shortwave radiation calculated by the ECHAM3/T106 model is overestimated by 45 W m–2 over most of Europe, which implies a largely unrealistic forcing on the model surface scheme and excessive surface temperatures. In winter, too little incoming shortwave radiation reaches the model surface. Similar tendencies are found over large areas of the mid-latitudes. These biases are consistent with deficiencies in the simulation of cloud amount, relative humidity and clear sky radiative transfer. The incoming longwave radiation is underestimated at the European GEBA stations predominantly in summer. This largely compensates for the excessive shortwave flux, leading to annual mean net radiation values over Europe close to observations due to error cancellation, a feature already noted in the simulated global mean values in an earlier study. Furthermore, the annual cycle of the simulated surface net radiation is strongly affected by the deficiencies in the simulated incoming shortwave radiation. The high horizontal resolution of the GCM allows an assessment of orographically induced flux gradients based on observations from the European Alps. Although the model-calculated and observed flux fields substantially differ in their absolute values, several aspects of their gradients are realistically captured. The deficiencies identified in the model fields are generally consistent at most stations, indicating a high degree of representativeness of the measurements for their larger scale setting. 相似文献
10.