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1.
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. |
2.
Based on daily rainfall data over a period of 80 years (1901–1980) taken at 75 stations, this paper reports interannual and long term fluctuations of the following parameters of the periods contributing each of 2, 5, 10, 20–90 and 95% rainfall to annual total over each of North Kerala and South Kerala rainfall subregions of India:
For most of the rainfall periods, the time series of starting and ending dates and length are homogeneous and random, and tend to observe the normal probability distribution. The different PCI series of North Kerala and the annual rainfall series of South Kerala show significantly decreasing trend which are indicative of considerable change in the hydroclimatic environment of Kerala. Possible changes in the southwest monsoon circulation along the west coast of India and excessive deforestation in Kerala which might have caused these rainfall changes are discussed. 相似文献
(i) | the starting date, |
(ii) | the ending date, |
(iii) | the length of the rainfall period or duration, |
(iv) | the total rainfall (which is a fixed percentage of the annual total) of the rainfall period, and |
(v) | the rainfall time-distribution characteristic which has been quantified by computing Oliver's precipitation concentration index (PCI) using daily rainfall data of the concerned rainfall period. |
3.
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. |
4.
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
5.
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. |
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.
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:
9.
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:
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.
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.
12.
Chidong Zhang Min Dong Silvio Gualdi Harry H. Hendon Eric D. Maloney Andrew Marshall Kenneth R. Sperber Wanqiu Wang 《Climate Dynamics》2006,27(6):573-592
The status of the numerical reproduction of the Madden–Julian Oscillation (MJO) by current global models was assessed through
diagnoses of four pairs of coupled and uncoupled simulations. Slow eastward propagation of the MJO, especially in low-level
zonal wind, is realistic in all these simulations. However, the simulated MJO suffers from several common problems. The MJO
signal in precipitation is generally too weak and often eroded by an unrealistic split of an equatorial maximum of precipitation
into a double ITCZ structure over the western Pacific. The MJO signal in low-level zonal wind, on the other hand, is sometimes
too strong over the eastern Pacific but too weak over the Indian Ocean. The observed phase relationship between precipitation
and low-level zonal wind associated with the MJO in the western Pacific and their coherence in general are not reproduced
by the models. The seasonal migration in latitude of MJO activity is missing in most simulations. Air–sea coupling generally
strengthens the simulated eastward propagating signal, but its effects on the phase relationship and coherence between precipitation
and low-level zonal wind, and on their geographic distributions, seasonal cycles, and interannual variability are inconsistent
among the simulations. Such inconsistency cautions generalization of results from MJO simulations using a single model. In
comparison to observations, biases in the simulated MJO appear to be related to biases in the background state of mean precipitation,
low-level zonal wind, and boundary-layer moisture convergence. This study concludes that, while the realistic simulations
of the eastward propagation of the MJO are encouraging, reproducing other fundamental features of the MJO by current global
models remains an unmet challenge.
13.
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.
14.
Decadal interactions between the western tropical Pacific and the North Atlantic Oscillation 总被引:5,自引:5,他引:0
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.
15.
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.
16.
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.
17.
In this study seasonal predictability of Tier-one and Tier-two predictions are evaluated and compared. Through the comparison
of these two predictions, it is demonstrated that the air–sea coupled process is an important factor not only for climatological
simulation but also for seasonal predictability. In particular, the air–sea coupling plays a crucial role over the warm pool
region, as the atmosphere tends to lead the ocean in anomalous variability. In this region, the Tier-one prediction has better
climatology compared to the Tier-two prediction despite the presence of a climatological SST bias. Furthermore, the Tier-one
has a relatively higher seasonal predictive skill than that of the Tier-two although its SST prediction skill is relatively
poor. It is suggested that the air–sea coupled process plays a role to reduce both the climatological and anomalous biases
in the uncoupled AGCM by means of the negative feedback of the SST-heat flux-precipitation loop. Using the CliPAS and DEMETER
seasonal prediction data, the robustness of these results are demonstrated in the multi-model frame works.
This paper is a contribution to the AMIP-CMIP Diagnostic Sub-project on General Circulation Model Simulation of the East Asian
Climate, coordinated by W.-C. Wang.
18.
19.
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.
20.
Julia V. Manganello 《Climate Dynamics》2008,30(6):621-641
The influence of sea surface temperature anomalies (SSTA) on multi-year persistence of the North Atlantic Oscillation (NAO)
during the second half of the twentieth century is investigated using the Center for Ocean-Land-Atmosphere Studies (COLA)
Atmospheric GCM (AGCM) with an emphasis on isolating the geographic location of the SSTA that produce this influence. The
present study focuses on calculating the atmospheric response to the SSTA averaged over 1988–1995 (1961–1968) corresponding
to the observed period of strong persistence of the positive (negative) phase of the decadal NAO. The model response to the
global 1988–1995 average SSTA shows a statistically significant large-scale pattern characteristic of the positive phase of
the NAO. Forcing with the global 1961–1968 average SSTA generates a NAO of the opposite polarity compared to observations.
However, all large-scale features both in the model and observations during this period are weaker in magnitude and less significant
compared to 1988–1995. Additional idealized experiments show that over the northern center of the NAO the non-linear component
of the forced response appears to be quite important and acts to enhance the positive NAO signal. On the other hand, over
the southern center where the model response is the strongest, it is also essentially linear. The 1988–1995 average SSTA restricted
to the western tropical Pacific region produce a positive NAO remarkably similar in structure but stronger in magnitude than
the model response to the global and tropical Indo-Pacific 1988–1995 forcing. A 200-hPa geopotential height response in these
experiments shows a positive anomaly over the southern center of the NAO embedded in the Rossby wave trains propagating from
the western tropical Pacific. Indian Ocean SSTA lead to much weaker positive NAO primarily through the effect on its northern
center. SST forcing confined to the North Atlantic north of equator does not produce a response statistically different from
the control simulation, suggesting that it is not strong enough to significantly affect the phase of the decadal NAO. Inclusion
of the South Atlantic north of 45° south does not change this result.
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