共查询到20条相似文献,搜索用时 482 毫秒
1.
R. E. Okoola 《Meteorology and Atmospheric Physics》1989,41(1):35-44
The First Garp Global Experiment data collected during 1979 at sea level and 850 mb level have been used to examine the origin and characteristics of the westwards moving disturbances in the western Indian Ocean.From the analyses of the above data the following sequence of events in the westwards moving disturbances has emerged:
相似文献
(i) | Increase (decrease) in the pressure of the Mascarene High causes intensification (weakening) of the meridional pressure gradient in the region between 25°S and the equator. |
(ii) | This increase in the pressure gradient in the region leads to increase in the zonal wind and convergence in the region. It is noteworthy that the zonal wind responds to the pressure near the Mascarene High at the quasi-biweekly period. |
(iii) | The increase in convergence at the surface and at 850 mb level, in the region equator to 5°S and between 60°E and 75°E, gives rise to the genesis of a disturbance in this region. |
(iv) | The disturbances are then carried westwards in the low level easterly winds to affect the Seychelles Islands and the eastern African coastal regions. |
2.
The convective heat transfer coefficient (CHTC) of an urban canopy is a crucial parameter for estimating the turbulent heat
flux in an urban area. We compared recent experimental research on the CHTC and the mass transfer coefficient (MTC) of urban
surfaces in the field and in wind tunnels. Our findings are summarised as follows.
Although there is some agreement in the measured values, our overall understanding of the CHTC remains too low for accurate
modelling of urban climate. 相似文献
(1) | In full-scale measurements on horizontal building roofs, the CHTC is sensitive to the height of the reference wind speed for heights below 1.5 m but is relatively independent of roof size. |
(2) | In full-scale measurements of vertical building walls, the dependence of the CHTC on wind speed is significantly influenced by the choice of the measurement position and wall size. The CHTC of the edge of the building wall is much higher than that near the centre. |
(3) | In spite of differences of the measurement methods, wind-tunnel experiments of the MTC give similar relations between the ratio of street width to canopy height in the urban canopy. Moreover, this relationship is consistent with known properties of the flow regime of an urban canopy. |
(4) | Full-scale measurements on roofs result in a non-dimensional CHTC several tens of times greater than that in scale-model experiments with the same Reynolds number. |
3.
The Institute of Atmospheric Physics Land Surface Model (IAP94) has been incorporated into the IAP two-level atmospheric general circulation model (IAP GCM). Global and regional climatology averaged over the last 25 years of 100 year integrations from the IAP GCM with and without IAP94 (“bucket” scheme) is compared. The simulated results are also compared with the reanalysis data. Major findings are:(1) The IAP GCM simulation without IAP94 has extensive regions of warmer than observed surface air tempera?tures, while the simulation with IAP94 very much improves the surface air temperature.(2) The IAP GCM simulation with IAP94 gives improvement of the simulated precipitation pattern and intensity, especially the precipitation of East Asian summer monsoon and its intraseasonal migration of the rainbelts.(3) In five selected typical regions, for most of the surface variables such as surface air temperature, precipitation, precipitation minus evaporation, net radiation, latent heat flux and sensible heat flux, the IAP GCM with IAP94 pro?vides better simulations. 相似文献
4.
The spatial auto-correlation of minimum temperature was analyzed for a topoclimatological station network in the Huleh Valley of Israel on radiation cooling nights, using the method of optimum interpolation. Only a few stations all of which are situated in a flat area along the longitudinal central axis, exhibited a distinct dependence of the auto-correlation with distance. These stations were less representative of the entire valley compared with sites close to the slopes.The more varied topography near the edges of the valley leaves its stamp on the auto-correlation field in two specific ways:
相似文献
(a) | Due to the more sloping surface, the increased randomness on the microscale diminishes and more generally obscures the dependence of the auto-correlation with distance from a given reference station. |
(b) | The increased mixing associated with the slope-induced airflow increases the areal auto-correlation surrounding a given station. |
5.
The microphysical model with the bulk water parameterization is applied to simulated both contact and deposition nucleation as well as the imersion freezing for unseeded cases and the cases immediately after seeding performed for the cold continental Cb clouds with small cloud droplets. The injection of agent AgI is performed in temperature region between –8°C and –12°C. The four groups of sensitivity experiments are executed.
With 14 Figures 相似文献
a. | The Brownian coagulation of rain drops is the most important contact nucleation mechanism for seeded cases with great amount of rain drops. When cloud droplets mainly contribute to the liquid water content for seeded cases, the Brownian coagulation of cloud droplets is the primary nucleation mechanism while the inertial impact is the less effective contact nucleation mechanism; |
b. | the mutual interdependence of contact and deposition nucleation mechanisms shows that the contact nucleation is more effective for graupel production than the deposition one for the temperature region considered in this model; |
c. | the imersion freezing is the most important mechanism for all cases with significant amount of rain drops. It is more effective than the contact nucleation mechanism in unseeded cases with insufficient number of rain drops; |
d. | the nucleation mechanisms are more sensitive to temperature changes than to pressure changes. |
6.
This paper discusses the retrieval scheme associated with the gas correlated radiometer- MOPITT which will be on board of EOS-AM1 to measure the global vertical profiles of car-bon monoxide. The vertical resolution and retrieval errors caused by errors in the temperature profiles and in the surface temperature have been assessed. The main results are: a. Assuming the noise equivalent radiance (NER) of 1.8 × 105 W m-2 sr-1, the surface tem?perature can be deduced from the wide band signals with uncertainly less than 1 K, and the atmospheric term of the modulated signal can be deduced with errors almost equal to the NER which does not significantly increase errors in the retrieved CO profiles. b. With typical uncertainty in temperature profiles, errors in the retrieved profiles at lati-? tudes lower than 70o are generally less than 20% with the first guess of 100 ppbv. (If a better first guess was used, the errors may decrease). c. By incorporating the total column CO amount derived from the reflected solar radiation in 2.3 μm spectral region into the retrieval, the accuracy of the retrieved CO profile below 6 km may be greatly improved. d. In the retrieval experiment with 10 CO profiles representing the typical CO profiles, the r.m.s. relative / absolute errors of the retrieved CO profiles are about 10% / 15-20 ppbv. 相似文献
7.
Jim Salinger 《Climatic change》2010,100(1):49-57
Birth is a beginning, 相似文献
8.
Rate coefficients have been measured for the reactions of hydroxyl radicals with five aliphatic ethers over the temperature range 242–328 K. Competitive studies were carried out in an atmospheric flow reactor in which the hydroxyl radicals were generated by the photolysis of methyl nitrite in the presence of air containing nitric oxide. The reaction of OH with 2,3-dimethyl-butane was used as the reference reaction and the following Arrhenius parameters have been obtained for the reactions: OH+RORproducts:
9.
The linear dynamics of the unstably stratified geophysical flows is investigated with a two-layer formulation. A ‘convective’ deformation radius classifies the dynamics into three regimes:
10.
Multi-century climate simulations obtained with the GISS atmospheric general circulation model coupled to the hybrid-isopycnic
ocean model HYCOM are described. Greenhouse gas concentrations are held fixed in these experiments to investigate the coupled
model’s ability to reproduce the major features of today’s climate with minimal drift. Emphasis is placed on the realism of
the oceanic general circulation and its effect on air–sea exchange processes. Several model runs using different closures
for turbulent vertical exchange as well as improvements to reduce vertical numerical diffusion are compared with climate observations.
As in previous studies, the Southern Ocean emerges as the Achilles Heel of the ocean model; deficiencies in its physical representation
had far-reaching consequences in early experiments with the coupled model and have provided the strongest impetus for model
improvement. The overarching goal of this work is to add diversity to the pool of ocean models available for climate prediction
and thereby reduce biases that may stand in the way of assessing climate prediction uncertainty.
11.
Future changes in cyclone climatology over Europe as inferred from a regional climate simulation 总被引:1,自引:0,他引:1
This study analyzes the cyclone climatology in regional climate model simulations of present day (1961–1990) and future (2071–2100,
A2 and B2 emission scenarios) european climate conditions. The model domain covers the area from Scandinavia to Northern Africa
and from the Eastern Atlantic to Russia at a horizontal grid spacing of 50 km. Compared to present day, in the A2 and B2 scenario
conditions the annual average storm track intensity increases over the North-East Atlantic and decreases over Russia and the
Eastern Mediterranean region. This overall change pattern is larger in the A2 than in the B2 simulations. However, the cyclone
climatology change signal shows a large intermonthly variability and important differences across European regions. The largest
changes are found over the North-East Atlantic, where the storm track intensity increases in winter and decreases in summer.
A significant reduction of storm track intensity is found during late summer and autumn over the Mediterranean region, and
from October to January over Russia. The number of cyclones decreases in future conditions throughout Europe, except over
the Central Europe and Mediterranean regions in summer (where it increases). The frequency of intense cyclones and the depth
of extreme cyclones increase over the North-East Atlantic, decrease over Russia and show an irregular response over the rest
of the domain.
12.
The relationship between interdecadal variations of tropical sea surface temperature (SST) in the last 120 years and circulation
anomalies related to the North Atlantic Oscillation (NAO) is investigated in this study. Using an atmospheric general circulation
model (AGCM), we confirm observational evidence that variations in the SST gradient in the western tropical Pacific are related
to the NAO anomalies on decadal timescale, and may be contributing to the shift towards the positive NAO phase observed in
the late 20th century. The role played by the Indian Ocean-NAO teleconnection, advocated in recent studies focused on the
last 50 years, is also assessed in the context of the 120-year long record. It is suggested that a positive feedback between
the Pacific SST and the hemispheric circulation pattern embedding the decadal NAO signal may act to enhance the internal variability
of the coupled ocean–atmosphere system, and justify the stronger teleconnection found in observational data than in SST-forced
AGCM experiments.
13.
Oscar Peralta Darrel Baumgardner Graciela B. Raga 《Journal of Atmospheric Chemistry》2007,57(2):153-169
Spectrothermography, defined as the evaluation of thermograms of carbon evolved from heated aerosol samples, is a technique
for evaluating differences in particle characteristics as they relate to emission sources and processes that modify particle
evolution. Here we describe the inherent uncertainties and demonstrate the utility of this technique with an evaluation of
samples that were collected with eight stage cascade impactors at three sites in Mexico City over a period of 5 months. The
study was implemented with statistical analysis based on tests for goodness of fit to separate thermograms with distinctive
shapes related to the relative amounts of organic and elemental carbon mass that evolves as a function of temperature. Thermograms
with unique shapes were found for particles with aerodynamic diameters of 1–10, 0.56–1, 0.32–0.56 and 0.18–0.32 μm with further
differentiation of curves related to the relative amounts of gasoline and diesel fuel that was combusted in the region of
the three sites. The common shapes fit 32–42% of samples in each particle size range and indicate that this type of analysis
can help distinguish differences in the primary sources of organic and elemental carbon.
14.
Guojun Gu 《Climate Dynamics》2009,32(4):457-471
Intraseasonal (30–80 days) variability in the equatorial Atlantic-West African sector during March–June is investigated using
various recently-archived satellite measurements and the NCEP/DOE AMIP-II reanalysis daily data. The global connections of
regional intraseasonal signals are first examined for the period of 1979–2006 through lag-regression analyses of convection
(OLR) and other dynamic components against a regional intraseasonal convective (OLR) index. The eastward-propagating features
of convection can readily be seen, accompanied by coherent circulation anomalies, similar to those for the global tropical
intraseasonal mode, i.e., the Madden–Julian oscillation (MJO). The regressed TRMM rainfall (3B42) anomalies during the TRMM
period (1998–2006) manifest similar propagating features as for the regressed OLR anomalies during 1979–2006. These coherent
features hence tend to suggest that the regional intraseasonal convective signals might be mostly a regional response to,
or closely associated with the MJO, and probably contribute to the MJO’s global propagation. Atmospheric and surface intraseasonal
variability during March–June of 1998–2006 are further examined using the high-quality TRMM Microwave Imager (TMI) sea surface
temperature (SST), columnar water vapor, and cloud liquid water, and the QuikSCAT oceanic winds (2000–2006). Enhanced (suppressed)
convection or positive (negative) rainfall anomalies approximately cover the entire basin (0°–10°N, 30°W–10°E) during the
passage of intraseasonal convective signals, accompanied by anomalous surface westerly (easterly) flow. Furthermore, a unique
propagating feature seems to exist within the tropical Atlantic basin. Rainfall anomalies always appear first in the northwestern
basin right off the coast of South America, and gradually extend eastward to cover the entire basin. A dipolar structure of
rainfall anomalies with cross-equatorial surface wind anomalies can thus be observed during this evolution, similar to the
anomaly patterns on the interannual time scale discovered in past studies. Coherent intraseasonal variations and patterns
can also be found in other physical components.
15.
The current generations of climate models are in substantial disagreement as to the projected patterns of sea surface temperatures (SSTs) in the Tropics over the next several decades. We show that the spatial patterns of tropical ocean temperature trends have a strong influence on global mean temperature and precipitation and on global mean radiative forcing. We identify the SST patterns with the greatest influence on the global mean climate and find very different, and often opposing, sensitivities to SST changes in the tropical Indian and West Pacific Oceans. Our work stresses the need to reduce climate model biases in these sensitive regions, as they not only affect the regional climates of the nearby densely populated continents, but also have a disproportionately large effect on the global climate.
16.
17.
Transient simulation of the last glacial inception. Part I: glacial inception as a bifurcation in the climate system 总被引:2,自引:2,他引:0
Reinhard Calov Andrey Ganopolski Martin Claussen Vladimir Petoukhov Ralf Greve 《Climate Dynamics》2005,24(6):545-561
We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which
encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional
polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at the Eemiam interglacial, at 126 ky
BP (126,000 years before present). The model runs for 26 kyr with time-dependent orbital and CO2 forcings. The model simulates a rapid expansion of the area covered by inland ice in the Northern Hemisphere, predominantly
over Northern America, starting at about 117 kyr BP. During the next 7 kyr, the ice volume grows gradually in the model at
a rate which corresponds to a change in sea level of 10 m per millennium. We have shown that the simulated glacial inception
represents a bifurcation transition in the climate system from an interglacial to a glacial state caused by the strong snow-albedo
feedback. This transition occurs when summer insolation at high latitudes of the Northern Hemisphere drops below a threshold
value, which is only slightly lower than modern summer insolation. By performing long-term equilibrium runs, we find that
for the present-day orbital parameters at least two different equilibrium states of the climate system exist—the glacial and
the interglacial; however, for the low summer insolation corresponding to 115 kyr BP, we find only one, glacial, equilibrium
state, while for the high summer insolation corresponding to 126 kyr BP only an interglacial state exists in the model.
18.
Katharine Hayhoe Cameron P. Wake Thomas G. Huntington Lifeng Luo Mark D. Schwartz Justin Sheffield Eric Wood Bruce Anderson James Bradbury Art DeGaetano Tara J. Troy David Wolfe 《Climate Dynamics》2007,28(4):381-407
To assess the influence of global climate change at the regional scale, we examine past and future changes in key climate,
hydrological, and biophysical indicators across the US Northeast (NE). We first consider the extent to which simulations of
twentieth century climate from nine atmosphere-ocean general circulation models (AOGCMs) are able to reproduce observed changes
in these indicators. We then evaluate projected future trends in primary climate characteristics and indicators of change,
including seasonal temperatures, rainfall and drought, snow cover, soil moisture, streamflow, and changes in biometeorological
indicators that depend on threshold or accumulated temperatures such as growing season, frost days, and Spring Indices (SI).
Changes in indicators for which temperature-related signals have already been observed (seasonal warming patterns, advances
in high-spring streamflow, decreases in snow depth, extended growing seasons, earlier bloom dates) are generally reproduced
by past model simulations and are projected to continue in the future. Other indicators for which trends have not yet been
observed also show projected future changes consistent with a warmer climate (shrinking snow cover, more frequent droughts,
and extended low-flow periods in summer). The magnitude of temperature-driven trends in the future are generally projected
to be higher under the Special Report on Emission Scenarios (SRES) mid-high (A2) and higher (A1FI) emissions scenarios than
under the lower (B1) scenario. These results provide confidence regarding the direction of many regional climate trends, and
highlight the fundamental role of future emissions in determining the potential magnitude of changes we can expect over the
coming century.
19.
Modelling of near-surface ozone over South Asia 总被引:2,自引:1,他引:1
Magnuz Engardt 《Journal of Atmospheric Chemistry》2008,59(1):61-80
Hourly, three-dimensional, fields of tropospheric ozone have been produced for 12 consecutive months on a domain covering
South Asia, using the regional Eulerian off-line chemistry transport model MATCH. The results were compared with background
observations to investigate diurnal and seasonal variations of near-surface ozone in the region. MATCH reproduced the seasonality
of near-surface ozone at most locations in the area. However, the current, and previous, studies indicate that the model consequently
overestimate night-time concentrations, while it occasionally underestimates the day-time, near-surface, ozone concentrations.
The lowest monthly-mean concentrations of near-surface ozone are typically experienced in June–September, coincident with
the rainy season in most areas. The seasonality is not identical across the domain; some locations have a completely different
trend. Large areas in Northern India and Nepal show a secondary minimum during the cold winter season (December–January).
High concentrations of near-surface ozone are found over the oceans, close to the Indian subcontinent, due to the less efficient
dry deposition to water surfaces; over parts of Tibet due to influence of free tropospheric air and little deposition to snow
covered surfaces; and along the Gangetic valley due to the large emissions of precursors in this region. Monthly-mean ozone
concentrations in the densely populated northern India range from 30–45 ppb(v). The model results were also used to produce maps of AOT40. The results point towards similar levels of AOT40 in India as
in Europe: large areas of India show 3-month AOT40 values above 3 ppm(v) hours.
20.
Role of soil freezing in future boreal climate change 总被引:3,自引:0,他引:3
We introduced a simple scheme of soil freezing in the LMDz3.3 atmospheric general circulation model (AGCM) to examine the potential effects of this parameterization on simulated future boreal climate change. In this multi-layer soil scheme, soil heat capacity and conductivity are dependent on soil water content, and a parameterization of the thermal and hydrological effects of water phase changes is included. The impact of these new features is evaluated against observations. By comparing present-day and 2×CO2 AGCM simulations both with and without the parameterization of soil freezing the role of soil freezing in climate change is analysed. Soil freezing does not have significant global impacts, but regional effects on simulated climate and climate change are important. In present-day conditions, hydrological effects due to freezing lead to dryer summers. In 2×CO2 climate, thermal effects due to freeze/thaw cycles are more pronounced and contribute to enhance the expected future overall winter warming. Impact of soil freezing on climate sensitivity is not uniform: the annual mean warming is amplified in North America (+15%) and Central Siberia (+36%) whereas it is reduced in Eastern Siberia (–23%). Nevertheless, all boreal lands undergo a strong attenuation of the warming during summertime. In agreement with some previous studies, these results indicate once more that soil freezing effects are significant on regional boreal climate. But this study also demonstrates its importance on regional boreal climate change and thus the necessity to include soil freezing in regional climate change predictions.
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