共查询到20条相似文献，搜索用时 152 毫秒
1.
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.
相似文献
| P. LionelloEmail: |
2.
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.
相似文献
| Fred KucharskiEmail: |
3.
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.
相似文献
| Julia V. ManganelloEmail: |
4.
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.
相似文献
| Shan Sun (Corresponding author)Email: |
| Rainer BleckEmail: |
5.
This study examines the variability of the monthly average significant wave height (SWH) field in the Mediterranean Sea, in
the period 1958–2001. The analysed data are provided by simulations carried out using the WAM model (WAMDI group, 1988) forced
by the wind fields of the ERA-40 (ECMWF Re-Analysis). Comparison with buoy observations, satellite data, and simulations forced
by higher resolution wind fields shows that, though results underestimate the actual SWH, they provide a reliable representation
of its real space and time variability. Principal component analysis (PCA) shows that the annual cycle is characterised by
two main empirical orthogonal functions (EOF) patterns. Most inter-monthly variability is associated with the first EOF, whose
positive/negative phase is due to the action of Mistral/Etesian wind regimes. The second EOF is related to the action of southerly
winds (Libeccio and Sirocco). The annual cycle presents two main seasons, winter and summer characterised, the first, by the
prevalence of eastwards and southeastwards propagating waves all over the basin, and the second, by high southwards propagating
waves in the Aegean Sea and Levantin Basin. Spring and fall are transitional seasons, characterised by northwards and northeastwards
propagating waves, associated to an intense meridional atmospheric circulation, and by attenuation and amplification, respectively,
of the action of Mistral. These wave field variability patterns are associated with consistent sea level pressure (SLP) and
surface wind field structures. The intensity of the SWH field shows large inter-annual and inter-decadal variability and a
statistically significant decreasing trend of mean winter values. The winter average SWH is anti-correlated with the winter
NAO (North Atlantic Oscillation) index, which shows a correspondingly increasing trend. During summer, a minor component of
the wave field inter-annual variability (associated to the second EOF) presents a statistically significant correlation with
the Indian Monsoon reflecting its influence on the meridional Mediterranean circulation. However, the SLP patterns associated
with the SWH inter-annual variability reveal structures different from NAO and Monsoon circulation. In fact, wave field variability
is conditioned by regional storminess in combination with the effect of fetch. The latter is likely to be the most important.
Therefore, the inter-annual variability of the mean SWH is associated to SLP patterns, which present their most intense features
above or close to Mediterranean region, where they are most effective for wave generation.
相似文献
| P. LionelloEmail: |
6.
Remotely forced variability in the tropical Atlantic Ocean 总被引：1，自引：1，他引：1
An ensemble of eight hindcasts has been conducted using an ocean-atmosphere general circulation model fully coupled only within the Atlantic basin, with prescribed observational sea surface temperature (SST) for 1950–1998 in the global ocean outside the Atlantic basin. The purpose of these experiments is to understand the influence of the external SST anomalies on the interannual variability in the tropical Atlantic Ocean. Statistical methods, including empirical orthogonal function analysis with maximized signal-to-noise ratio, have been used to extract the remotely forced Atlantic signals from the ensemble of simulations. It is found that the leading external source on the interannual time scales is the El Niño/Southern Oscillation (ENSO) in the Pacific Ocean. The ENSO signal in the tropical Atlantic shows a distinct progression from season to season. During the boreal winter of a maturing El Niño event, the model shows a major warm center in the southern subtropical Atlantic together with warm anomalies in the northern subtropical Atlantic. The southern subtropical SST anomalies is caused by a weakening of the southeast trade winds, which are partly associated with the influence of an atmospheric wave train generated in the western Pacific Ocean and propagating into the Atlantic basin in the Southern Hemisphere during boreal fall. In the boreal spring, the northern tropical Atlantic Ocean is warmed up by a weakening of the northeast trade winds, which is also associated with a wave train generated in the central tropical Pacific during the winter season of an El Niño event. Apart from the atmospheric planetary waves, these SST anomalies are also related to the sea level pressure (SLP) increase in the eastern tropical Atlantic due to the global adjustment to the maturing El Niño in the tropical Pacific. The tropical SLP anomalies are further enhanced in boreal spring, which induce anomalous easterlies on and to the south of the equator and lead to a dynamical oceanic response that causes cold SST anomalies in the eastern and equatorial Atlantic from boreal spring to summer. Most of these SST anomalies persist into the boreal fall season.
相似文献
| B. HuangEmail: |
7.
Extratropical cyclone variability in the Northern Hemisphere winter from the NCEP/NCAR reanalysis data 总被引：9，自引：0，他引：9
The winter climatology of Northern Hemisphere cyclone activity was derived from 6-hourly NCEP/NCAR reanalysis data for the
period from 1958 to 1999, using software which provides improved accuracy in cyclone identification in comparison to numerical
tracking schemes. Cyclone characteristics over the Kuroshio and Gulfstream are very different to those over continental North
America and the Arctic. Analysis of Northern Hemisphere cyclones shows secular and decadal-scale changes in cyclone frequency,
intensity, lifetime and deepening rates. The western Pacific and Atlantic are characterized by an increase in cyclone intensity
and deepening during the 42-year period, although the eastern Pacific and continental North America demonstrate opposite tendencies
in most cyclone characteristics. There is an increase of the number of cyclones in the Arctic and in the western Pacific and
a downward tendency over the Gulf Stream and subpolar Pacific. Decadal scale variability in cyclone activity over the Atlantic
and Pacific exhibits south-north dipole-like patterns. Atlantic and Pacific cyclone activity associated with the NAO and PNA
is analyzed. Atlantic cyclone frequency demonstrates a high correlation with NAO and reflects the NAO shift in the mid 1970s,
associated with considerable changes in European storm tracks. The PNA is largely linked to the eastern Pacific cyclone frequencies,
and controls cyclone activity over the Gulf region and the North American coast during the last two decades. Assessment of
the accuracy of the results and comparison with those derived using numerical algorithms, shows that biases inherent in numerical
procedures are not negligible.
Received: 7 July 2000 / Accepted: 30 November 2000 相似文献
8.
9.
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.
相似文献
| Joseph J. BarsugliEmail: Phone: +1-303-4976042Fax: +1-303-4976449 |
10.
N. A. Vyazilova 《Russian Meteorology and Hydrology》2012,37(7):431-437
Carried out is the comparative analysis of the cyclone activity for different combinations of positive and negative values of the North Atlantic Oscillation (NAO) and East Atlantic Oscillation (EA) indices. The integral characteristics of the cyclone activity (density and intensity of cyclones) are computed on the basis of the method of automatic indication of cyclone centers from the sea-level pressure data. It is demonstrated that the NAO index is really the major indicator of cyclone activity anomaly formation in the North Atlantic, however, the variations of cyclone activity in the European region, of the number of cyclones and their integral intensity are better characterized by the EA index. 相似文献
11.
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.
相似文献
| In-Sik KangEmail: |
12.
Analysis of the projected regional sea-ice changes in the Southern Ocean during the twenty-first century 总被引：2，自引：1，他引：1
Using the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) for the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change (IPCC AR4), the projected regional distribution of sea ice for the
twenty-first century has been investigated. Averaged over all those model simulations, the current climate is reasonably well
reproduced. However, this averaging procedure hides the errors from individual models. Over the twentieth century, the multimodel
average simulates a larger sea-ice concentration decrease around the Antarctic Peninsula compared to other regions, which
is in qualitative agreement with observations. This is likely related to the positive trend in the Southern Annular Mode (SAM)
index over the twentieth century, in both observations and in the multimodel average. Despite the simulated positive future
trend in SAM, such a regional feature around the Antarctic Peninsula is absent in the projected sea-ice change for the end
of the twenty-first century. The maximum decrease is indeed located over the central Weddell Sea and the Amundsen–Bellingshausen
Seas. In most models, changes in the oceanic currents could play a role in the regional distribution of the sea ice, especially
in the Ross Sea, where stronger southward currents could be responsible for a smaller sea-ice decrease during the twenty-first
century. Finally, changes in the mixed layer depth can be found in some models, inducing locally strong changes in the sea-ice
concentration.
相似文献
| W. LefebvreEmail: |
13.
Sensitivity of sea ice to wind-stress and radiative forcing since 1500: a model study of the Little Ice Age and beyond 总被引：3，自引：2，他引：1
Three different reconstructed wind-stress fields which take into account variations of the North Atlantic Oscillation, one
general circulation model wind-stress field, and three radiative forcings (volcanic activity, insolation changes and greenhouse
gas changes) are used with the UVic Earth System Climate Model to simulate the surface air temperature, the sea-ice cover,
and the Atlantic meridional overturning circulation (AMOC) since 1500, a period which includes the Little Ice Age (LIA). The
simulated Northern Hemisphere surface air temperature, used for model validation, agrees well with several temperature reconstructions.
The simulated sea-ice cover in each hemisphere responds quite differently to the forcings. In the Northern Hemisphere, the
simulated sea-ice area and volume during the LIA are larger than the present-day area and volume. The wind-driven changes
in sea-ice area are about twice as large as those due to thermodynamic (i.e., radiative) forcing. For the sea-ice volume,
changes due to wind forcing and thermodynamics are of similar magnitude. Before 1850, the simulations suggest that volcanic
activity was mainly responsible for the thermodynamically produced area and volume changes, while after 1900 the slow greenhouse
gas increase was the main driver of the sea-ice changes. Changes in insolation have a small effect on the sea ice throughout
the integration period. The export of the thicker sea ice during the LIA has no significant effect on the maximum strength
of the AMOC. A more important process in altering the maximum strength of the AMOC and the sea-ice thickness is the wind-driven
northward ocean heat transport. In the Southern Hemisphere, there are no visible long-term trends in the simulated sea-ice
area or volume since 1500. The wind-driven changes are roughly four times larger than those due to radiative forcing. Prior
to 1800, all the radiative forcings could have contributed to the thermodynamically driven changes in area and volume. In
the 1800s the volcanic forcing was dominant, and during the first part of the 1900s both the insolation changes and the greenhouse
gas forcing are responsible for thermodynamically produced changes. Finally, in the latter part of the 1900s the greenhouse
gas forcing is the dominant factor in determining the sea-ice changes in the Southern Hemisphere.
相似文献
| Jan SedláčekEmail: |
14.
Climatology and interannual variations of wintertime extratropical cyclone frequency in CCSM3 twentieth century simulation
are compared with the NCEP/NCAR reanalysis during 1950–1999. CCSM3 can simulate the storm tracks reasonably well, although
the model produces slightly less cyclones at the beginning of the Pacific and Atlantic storm tracks and weaker poleward deflection
over the Pacific. As in the reanalysis, frequency of cyclones stronger than 980 hPa shows significant correlation with the
Pacific/North America (PNA) teleconnection pattern over the Pacific region and with the North Atlantic Oscillation (NAO) in
the Atlantic sector. Composite maps are constructed for opposite phases of El Nino-Southern Oscillation (ENSO) and the NAO
and all anomalous patterns coincide with observed. One CCSM3 twenty-first century A1B scenario realization indicates there
is significant increase in the extratropical cyclone frequency on the US west coast and decrease in Alaska. Meanwhile, cyclone
frequency increases from the Great Lakes region to Quebec and decreases over the US east coast, suggesting a possible northward
shift of the Atlantic storm tracks under the warmer climate. The cyclone frequency anomalies are closely linked to changes
in seasonal mean states of the upper-troposphere zonal wind and baroclinicity in the lower troposphere. Due to lack of 6-hourly
outputs, we cannot apply the cyclone-tracking algorithm to the other eight CCSM3 realizations. Based on the linkage between
the mean state change and the cyclone frequency anomalies, it is likely a common feature among the other ensemble members
that cyclone activity is reduced on the East Coast and in Alaska as a result of global warming. 相似文献
15.
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.
相似文献
| Katharine HayhoeEmail: |
16.
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.
相似文献
| Darrel BaumgardnerEmail: |
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.
相似文献
| Reinhard CalovEmail: |
18.
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.
相似文献
| Magnuz EngardtEmail: |
19.
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.
相似文献
| Chidong ZhangEmail: |
20.
The greening of the McGill Paleoclimate Model. Part I: Improved land surface scheme with vegetation dynamics 总被引：1，自引：1，他引：0
The formulation of a new land surface scheme (LSS) with vegetation dynamics for coupling to the McGill Paleoclimate Model (MPM) is presented. This LSS has the following notable improvements over the old version: (1) parameterization of deciduous and evergreen trees by using the models climatology and the output of the dynamic global vegetation model, VECODE (Brovkin et al. in Ecological Modelling 101:251–261 (1997), Global Biogeochemical Cycles 16(4):1139, (2002)); (2) parameterization of tree leaf budburst and leaf drop by using the models climatology; (3) parameterization of the seasonal cycle of the grass leaf area index; (4) parameterization of the seasonal cycle of tree leaf area index by using the time-dependent growth of the leaves; (5) calculation of land surface albedo by using vegetation-related parameters, snow depth and the models climatology. The results show considerable improvement of the models simulation of the present-day climate as compared with that simulated in the original physically-based MPM. In particular, the strong seasonality of terrestrial vegetation and the associated land surface albedo variations are in good agreement with several satellite observations of these quantities. The application of this new version of the MPM (the green MPM) to Holocene millennial-scale climate changes is described in a companion paper, Part II.
相似文献
| Yi WangEmail: Phone: +1-514-3987448Fax: +1-514-3986115 |