共查询到20条相似文献，搜索用时 15 毫秒
1.
We present an analysis of the factors which control the seasonal variations of the clear-sky greenhouse effect, based on satellite observations and radiative transfer simulations. The satellite observations include the radiation budget at the top of the atmosphere from the Earth Radiation Budget Experiment and the total column moisture content derived from the Special Sensor Microwave/Imager. The simulations were performed with the SAMSON system described in an earlier paper, using atmospheric temperatures and humidities from operational analyses produced by the European Centre for Medium Range Weather Forecasts. At low latitudes, the magnitude of the clear-sky greenhouse effect is dominated by the strong thermodynamic link between the total column moisture content of the atmosphere and sea surface temperatures, with minimal seasonal variations. In contrast, at middle to high latitudes there are strong seasonal variations, the clear-sky greenhouse effect being largest in winter and smallest in summer. These variations cannot be explained by the seasonal cycle in the total column moisture content, as this is largest in summer and smallest in winter. The variations are controlled instead by the seasonal changes in atmospheric temperatures. The colder atmosphere in winter enhances the temperature differential between the atmosphere and the sea surface, leading to a larger greenhouse effect despite the lower moisture contents. The magnitude of the clear-sky greenhouse effect is thus controlled by atmospheric humidity at low latitudes, but by atmospheric temperature at middle and high latitudes. These controls are illustrated by results from sensitivity experiments with SAMSON and are interpreted in terms of a simple model. 相似文献
2.
Summary The greenhouse effect has been investigated predominantly with satellite measurements, but more than 90% of the greenhouse radiative flux affecting Earths surface temperature and humidity originates from a 1000 meter layer above the surface. Here we show that substantial improvements on surface longwave radiation measurements and very good agreement with radiative transfer model calculations allow the clear-sky greenhouse effect be determined with measured surface longwave radiation and calculated longwave outgoing radiation at the top of the atmosphere. The cloud radiative forcing is determined by measured net longwave fluxes and added to the clear-sky greenhouse effect to determine the all-sky greenhouse effect. Longwave radiation measurements at different altitudes were used to determine the clear-sky and all-sky annual and seasonal greenhouse effect and altitude gradients over the Alps. Linear altitude gradients are measured for clear-sky situations, whereas the all-sky greenhouse effect is strongly influenced by varying, cloud amounts at different altitudes. Large diurnal and seasonal variations show the importance of surface heating and cooling effects and demonstrate the strong coupling of the greenhouse effect to surface temperature and humidity. 相似文献
3.
This study presents a comparison of the water vapor and clear-sky greenhouse effect dependence on sea surface temperature for climate variations of different types. Firstly, coincident satellite observations and meteorological analyses are used to examine seasonal and interannual variations and to evaluate the performance of a general circulation model. Then, this model is used to compare the results inferred from the analysis of observed climate variability with those derived from global climate warming experiments. One part of the coupling between the surface temperature, the water vapor and the clear-sky greenhouse effect is explained by the dependence of the saturation water vapor pressure on the atmospheric temperature. However, the analysis of observed and simulated fields shows that the coupling is very different according to the type of region under consideration and the type of climate forcing that is applied to the Earth-atmosphere system. This difference, due to the variability of the vertical structure of the atmosphere, is analyzed in detail by considering the temperature lapse rate and the vertical profile of relative humidity. Our results suggest that extrapolating the feedbacks inferred from seasonal and short-term interannual climate variability to longer-term climate changes requires great caution. It is argued that our confidence in climate models' predictions would be increased significantly if the basic physical processes that govern the variability of the vertical structure of the atmosphere, and its relation to the large-scale circulation, were better understood and simulated. For this purpose, combined observational and numerical studies focusing on physical processes are needed. 相似文献
4.
Delayed impact of El Niño on Tropical Indian Ocean (TIO) Sea Surface Temperature (SST) variations and associated physical mechanisms are well documented by several studies. However, TIO SST evolution during the decay phase of La Niña and related processes are not adequately addressed before. Strong cooling associated with La Niña decay over the TIO could influence climate over the Indian Oceanic rim including Indian summer monsoon circulation and remotely northwest Pacific circulation. Thus understanding the TIO basin-wide cooling and related physical mechanisms during decaying La Niña years is important. Composite analyses revealed that negative SST anomalies allied to La Niña gradually dissipate from its mature phase (winter) till subsequent summer in central and eastern Pacific. In contrast, magnitude of negative SST anomalies in TIO, induced by La Niña, starts increasing from winter and attains their peak values in early summer. It is found that variations in heat flux play an important role in SST cooling over the central and eastern equatorial Indian Ocean, Bay of Bengal and part of Arabian Sea from late winter to early summer during the decay phase of La Niña. Ocean dynamical processes are mainly responsible for the evolution of southern TIO SST cooling. Strong signals of westward propagating upwelling Rossby waves between 10°S to 20°S are noted throughout (the decaying phase of La Niña) spring and summer. Anomalous cyclonic wind stress curl to the south of the equator is responsible for triggering upwelling Rossby waves over the southeastern TIO. Further, upwelling Rossby waves are also apparent in the Arabian Sea from spring to summer and partly contributing to the SST cooling. Heat budget analysis reveals that negative SST/MLT (mixed layer temperature) anomalies over the Arabian Sea are mostly controlled by heat flux from winter to spring and vertical advection plays an important role during early summer. Vertical and horizontal advection terms primarily contribute to the SST cooling anomalies over southern TIO and the Bay of Bengal cooling is primarily dominated by heat flux. Further we have discussed influence of TIO cooling on local rainfall variations. 相似文献
5.
Water Resources of the South Asian Region in a Warmer Atmosphere 总被引：1，自引：0，他引：1
The global mean surface temperature may rise by about 0.3oC per decade during the next Few decades as a result of anthropogenic greenhouse gas emissions in the earth’s atmosphere. The data generated in the greenhouse warming simulations (Business-as-Usual scenario of IPCC) with the climate models developed at Max Planck Institute for Meteorology, Hamburg have been used to assess future plausible hydrological scenario for the South Asian region. The model results indicate enhanced surface warming (2.7oC for summer and 3.6oC for winter) over the land regions of South Asia during the next hundred years. While there is no significant change in the precipitation over most of the land regions during winter, substantial increase in precipitation is likely to occur during summer. As a result, an increase in soil moisture is likely over central India, Bangladesh and South China during summer but a statistically sig-nificant decline in soil moisture is expected over central China in winter. A moderate decrease in surface runoff may occur over large areas of central China during winter while the flood prone areas of NE-India. Bangladesh and South China are likely to have an increase in surface runoff during summer by the end of next century. 相似文献
6.
In this work, we have investigated the evolution of the summer air–sea interaction in the North Atlantic Ocean and the physical
processes involved using reanalysis data and model simulation. It is found that an atmosphere disturbance over the North Atlantic
Ocean in the preceding winter favors the build-up of a North Atlantic horseshoe-like sea surface temperature anomaly (SSTA)
pattern in the summer through modifying the northeast trade winds and changing ocean upwelling and downwelling. The changed
ocean condition (SSTA, upwelling, and downwelling) further intensifies the atmosphere disturbance as a positive feedback.
The thermal advection of the atmosphere disturbance weakens the SSTA pattern in the following autumn and winter. The anomalous
circulation associated with the air–sea interaction in the observations is characterized by a barotropic structure in the
middle and high latitudes of the North Atlantic Ocean. The baroclinic component is enhanced in the model simulation, particularly
in the seasons from summer to winter. The life cycle of the air–sea interaction is about 1 year in both the observations and
simulations. 相似文献
7.
A diagnostic study of heat transfer within the lower atmosphere and between the atmosphere and the surface of the Arctic Ocean
snow/ice pack during clear-sky conditions is conducted using data from the Surface Heat Budget of the Arctic Ocean (SHEBA)
field experiment. Surface heat budgets computed for four cloudy and four clear periods show that, while the net turbulent
heat fluxes at the surface are small during the cloudy periods, during the clear-sky periods they are a considerable source
of surface heating, balancing significant portions of the conductive heat fluxes from within the snow/ice pack. Analysis of
the dynamics and thermodynamics of the lower atmosphere during the clear-sky periods reveals that a considerable portion of
the heat lost to the surface by turbulent heat fluxes is balanced by locally strong heating near the atmospheric boundary-layer
(ABL) top due to the interaction of subsiding motions with the strong overlying temperature inversions surmounting the ABL.
This heat is then entrained into the ABL and transported to the surface by turbulent mixing, maintained by a combination of
vertical wind shear and wave-turbulence interactions. The frequency of stable, clear-sky periods, particularly during the
winter, combined with these results, suggests that the downward transfer of heat through the lower atmosphere and into the
surface represents an important component of the heat budgets of the lower atmosphere and snow/ice pack over the annual cycle 相似文献
8.
Fangxing Tian Buwen Dong Jon Robson Rowan Sutton Laura Wilcox 《Climate Dynamics》2020,54(9):3959-3975
In the period 1960–2010, the land surface air temperature (SAT) warmed more rapidly over some regions relative to the global mean. Using a set of time-slice experiments, we highlight how different physical processes shape the regional pattern of SAT warming. The results indicate an essential role of anthropogenic forcing in regional SAT changes from the 1970s to 2000s, and show that both surface–atmosphere interactions and large-scale atmospheric circulation changes can shape regional responses to forcing. Single forcing experiments show that an increase in greenhouse gases can lead to regional changes in land surface warming in winter (DJF) due to snow-albedo feedbacks, and in summer (JJA) due to soil-moisture and cloud feedbacks. Changes in anthropogenic aerosol and precursor (AA) emissions induce large spatial variations in SAT, characterized by warming over western Europe, Eurasia, and Alaska. In western Europe, SAT warming is stronger in JJA than in DJF due to substantial increases in clear sky shortwave radiation over Europe, associated with decreases in local AA emissions since the 1980s. In Alaska, the amplified SAT warming in DJF is due to increased downward longwave radiation, which is related to increased water vapor and cloud cover. In this case, although the model was able to capture the regional pattern of SAT change, and the associated local processes, it did not simulate all processes and anomalies correctly. For the Alaskan warming, the model is seen to achieve the correct regional response in the context of a wider North Pacific anomaly that is not consistent with observations. This demonstrates the importance of model evaluation that goes beyond the target variable in detection and attribution studies. 相似文献
9.
In this paper, the changes in convective activity over heat-low region over northwest India during contrasting phases of effective strength index (ESI) tendency have been examined. During contrasting phases of ESI tendency, evolution of surface pressure and temperature field over India from winter to spring is exactly opposite, and hence, the heat-low over northwest India depicts temporal and spatial variations in magnitude and location. During positive ESI tendency, the evolution of surface cooling and high surface pressure from winter to spring suggests reduced convective activity over heat-low region, while during the negative phase of ESI tendency, anomalously warm surface temperatures and low surface pressure evolve from winter to spring suggesting enhanced convective activity over the heat low region. The temporal variability in the relationship between surface temperature/pressure over heat-low region and Indian summer monsoon rainfall (ISMR) is also examined in this paper. During positive ESI tendency, heat-low temperature anomaly in February is significantly associated with ISMR, whereas during negative ESI tendency, both temperature/pressure over heat-low region in May are significantly associated with ISMR. These parameters may help in long range forecasting of ISMR. 相似文献
10.
This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990 s. Observations indicate an abrupt increase in summer mean surface air temperature(SAT) over Northeast Asia since the mid-1990 s. Accompanying this abrupt surface warming, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature(Tmax), daily minimum temperature(Tmin), annual hottest day temperature(TXx), and annual warmest night temperature(TNx) were observed. There were also increases in the frequency of summer days(SU) and tropical nights(TR).Atmospheric general circulation model experiments forced by changes in sea surface temperature(SST)/ sea ice extent(SIE),anthropogenic greenhouse gas(GHG) concentrations, and anthropogenic aerosol(AA) forcing, relative to the period 1964–93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes,although the abrupt decrease in precipitation since the mid-1990 s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA(through aerosol–radiation and aerosol–cloud interactions), mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere–land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply that the abrupt summer surface warming and increases in hot temperature extremes over Northeast Asia since the mid-1990 s will probably sustain in the next few decades as GHG concentrations continue to increase and AA precursor emissions over both North America and Europe continue to decrease. 相似文献
11.
12.
Qinglong You Arturo Sanchez-Lorenzo Martin Wild Doris Folini Klaus Fraedrich Guoyu Ren Shichang Kang 《Climate Dynamics》2013,40(7-8):2073-2086
In this study, the annual and seasonal variations of all-sky and clear-sky surface solar radiation (SSR) in the eastern and central Tibetan Plateau (TP) during the period 1960–2009 are investigated, based on surface observational data, reanalyses and ensemble simulations with the global climate model ECHAM5-HAM. The mean annual all-sky SSR series shows a decreasing trend with a rate of ?1.00 Wm?2 decade?1, which is mainly seen in autumn and secondly in summer and winter. A stronger decrease of ?2.80 Wm?2 decade?1 is found in the mean annual clear-sky SSR series, especially during winter and autumn. Overall, these results confirm a tendency towards a decrease of SSR in the TP during the last five decades. The comparisons with reanalysis show that both NCEP/NCAR and ERA-40 reanalyses do not capture the decadal variations of the all-sky and clear-sky SSR. This is probably due to a missing consideration of aerosols in the reanalysis assimilation model. The SSR simulated with the ECHAM5-HAM global climate model under both all-sky and clear-sky conditions reproduce the decrease seen in the surface observations, especially after 1980. The steadily increasing aerosol optical depth (AOD) at 550 nm over the TP in the ECHAM5-HAM results suggests transient aerosol emissions as a plausible cause. 相似文献
13.
Mellissa C. MacKellar Hamish A. McGowan Stuart R. Phinn Joshua S. Soderholm 《Boundary-Layer Meteorology》2013,146(2):319-340
Over warm, shallow coral reefs the surface radiation and energy fluxes differ from those of the open ocean and result in modification to the marine atmospheric boundary layer via the development of convective internal boundary layers. The complex interrelationships between the surface energy balance and boundary-layer characteristics influence local weather (wind, temperature, humidity) and hydrodynamics (water temperature and currents), as well as larger scale processes, including cloud field properties and precipitation. The nature of these inter-relationships has not been accurately described for coral reef environments. This study presents the first measurements of the surface energy balance, radiation budget and boundary layer thermodynamics made over a coral reef using an eddy-covariance system and radiosonde aerological profiling of the lower atmosphere. Results show that changes in surface properties and the associated energetics across the ocean-reef boundary resulted in modification to the marine atmospheric boundary layer during the Austral winter and summer. Internal convective boundary layers developed within the marine atmospheric boundary layer over the reef and were found to be deeper in the summer, yet more unstable during the winter when cold and drier flow from the mainland enhances heat and moisture fluxes to the atmosphere. A mixed layer was identified in the marine atmospheric boundary layer varying from 375 to 1,200 m above the surface, and was deeper during the summer, particularly under stable anticyclonic conditions. Significant cloud cover and at times rain resulted in the development of a stable stratified atmosphere over the reef. Our findings show that, for Heron Reef, a lagoonal platform reef, there was a horizontal discontinuity in surface energy fluxes across the ocean-reef boundary, which modified the marine atmospheric boundary layer. 相似文献
14.
异常东亚冬季风对夏季南海地区风场及热力场的影响 总被引：18，自引：1，他引：17
用合成及SVD方法,对冬季风异常在南海地区的风场和热力场中所产生的影响进行了研究,并探讨了这种相互联系的可能机制。结果表明,冬季风异常对流场的影响可以从冬季持续至春、夏季。在强冬季风年,南海夏季风爆发偏早、偏强且突发性显著;而在弱冬季风年则相反。长江流域的情况则与此相反,强冬季风时,该地区夏季对流偏弱,降水减少;弱冬季风时相反。南海地区风场的变化与该地区大气及下垫面热状态的改变有关。强、弱冬季风所对应的同期及后期的海温截然不同。在强冬季风年,热带海温场上呈现LaNi*S～/n@a型的异常分布,而在亚洲大陆近海及南海地区,则维持较强的负距平,海水温度明显偏低,强度以春季为最强。它所形成的南海及邻近地区海陆之间的温度梯度有利于夏季风的早爆发和加强;而在弱季风年,则完全相反。与异常冬季风相关联的大气的热状态同样具有季节的持续性。春、夏季季风区中大气热状态的改变,影响了夏季风特别是南海夏季风爆发的早晚及其强度的变化。由冬季风异常引起的热源变化可能也是环流隔季相关的重要纽带之一。 相似文献
15.
Impact of Indian monsoon on the coupled atmosphere/ocean system in the tropical pacific 总被引：12，自引：0，他引：12
T. Yasunari 《Meteorology and Atmospheric Physics》1990,44(1-4):29-41
Summary This study addresses the relationship between the Indian summer monsoon (ISM) and the coupled atmosphere/ocean system in the tropical Pacific on the interannual time scales. High positive correlations are found between ISM rainfall and both mixed layer sea water temperature (SWT) and sea surface temperature (SST) anomalies of the tropical western Pacific in the following winter. Negative correlations between ISM rainfall and SST in the central/eastern Pacific also appear to be most significant in the following winter. These parameters are correlated with each other mainly on a biennial time scale. Lag-correlations between the zonal wind and SST along the the equatorial Pacific show that the westerly (easterly) surface wind stress anomalies over the central/western Pacific are greatly responsible for the formation of negative (positive) SST/SWT anomalies in the western Pacific and positive (negative) SST/SWT anomalies in the central/eastern Pacific. Furthermore, it is evidenced that these lagcorrelations are physically based on the anomalies in the large-scale convection over the Asian monsoon region and the associated east-west circulation over the tropical Pacific, which first appear during the Indian summer monsoon season and evolve during the following autumn and winter. These results strongly suggest that the Asian summer monsoon may have an active, rather than a passive, role on the interannual variability, including the ENSO events, of the coupled atmosphere/ocean system over the tropical Pacific.With 9 Figures 相似文献
16.
One-Dimensional Variational Retrieval of Temperature and Humidity Profiles from the FY4A GIIRS 总被引：1，自引：0，他引：1
A physical retrieval approach based on the one-dimensional variational(1 D-Var) algorithm is applied in this paper to simultaneously retrieve atmospheric temperature and humidity profiles under both clear-sky and partly cloudy conditions from FY-4 A GIIRS(geostationary interferometric infrared sounder) observations. Radiosonde observations from upper-air stations in China and level-2 operational products from the Chinese National Satellite Meteorological Center(NSMC)during the periods from December 2019 to January 2020(winter) and from July 2020 to August 2020(summer) are used to validate the accuracies of the retrieved temperature and humidity profiles. Comparing the 1 D-Var-retrieved profiles to radiosonde data, the accuracy of the temperature retrievals at each vertical level of the troposphere is characterized by a root mean square error(RMSE) within 2 K, except for at the bottom level of the atmosphere under clear conditions. The RMSE increases slightly for the higher atmospheric layers, owing to the lack of temperature sounding channels there.Under partly cloudy conditions, the temperature at each vertical level can be obtained, while the level-2 operational products obtain values only at altitudes above the cloud top. In addition, the accuracy of the retrieved temperature profiles is greatly improved compared with the accuracies of the operational products. For the humidity retrievals, the mean RMSEs in the troposphere in winter and summer are both within 2 g kg–1. Moreover, the retrievals performed better compared with the ERA5 reanalysis data between 800 h Pa and 300 h Pa both in summer and winter in terms of RMSE. 相似文献
17.
基于青藏高原地区高质量、均一化的气象站点观测资料,研究1981—2010年青藏高原地区气温变化趋势特征。结果表明:1981—2010年青藏高原地区整体呈升温趋势,平均升温率为0.40℃/10a,冬春季升温率大于夏秋季节,以三江源区、西藏中西部和青海北部升温趋势最为显著。青藏高原地区年和冬、春、秋三季的升温率随海拔高度的升高而增大,海拔每升高1000 m,站点年平均气温倾向率增加0.1℃/10a,冬季更为显著。青藏高原地区夏季气温倾向率的空间分布具有显著的经向差异,纬度每增加10°,气温倾向率增加0.33℃/10a。 相似文献
18.
森林下垫面陆面物理过程及局地气候效应的数值模拟试验 总被引：5，自引：0，他引：5
文中基于大气边界层和植被冠层微气象学基本原理 ,建立了一个森林植被效应的陆面物理过程和二维大气边界层数值模式。并应用该模式进行了植被和土壤含水量等生物和生理过程在陆面过程和局地气候效应方面的数值模拟试验。所得数值模拟试验结果与实际情况相吻合。结果表明 ,应用该模式可获得植被温度、植被冠层内空气温度、地表温度日变化特征 ;森林下垫面大气边界层风速、位温、比湿、湍流交换系数的时空分布和日变化特征。该模式还可应用于不同下垫面 ,模拟陆面物理过程与大气边界层相互作用机制及其局地气候效应的研究 ,这将为气候模式与生物圈的耦合研究奠定一个良好的基础。 相似文献
19.
The sea surface temperature （SST） anomaly of the eastern Indian Ocean （EIO） exhibits cold anomalies in the boreal summer or fall during E1 Nino development years and warm anomalies in winter or spring following the E1 Nino events. There also tend to be warm anomalies in the boreal summer or fall during La Nina development years and cold anomalies in winter or spring following the La Nina events. The seasonal phase-locking of SST change in the EIO associated with E1 Nino/Southern Oscillation is linked to the variability of convection over the maritime continent, which induces an atmospheric Rossby wave over the EIO. Local air-sea interaction exerts different effects on SST anomalies, depending on the relationship between the Rossby wave and the mean flow related to the seasonal migration of the buffer zone, which shifts across the equator between summer and winter. The summer cold events start with cooling in the Timor Sea, together with increasing easterly flow along the equator. Negative SST anomalies develop near Sumatra, through the interaction between the atmospheric Rossby wave and the underneath sea surface. These SST anomalies are also contributed to by the increased upwelling of the mixed layer and the equatorward temperature advection in the boreal fall. As the buffer zone shifts across the equator towards boreal winter, the anomalous easterly flow tends to weaken the mean flow near the equator, and the EIO SST increases due to the reduction of latent heat flux from the sea surface. As a result, wintertime SST anomalies appear with a uniform and nearly basin-wide pattern beneath the easterly anomalies. These SST anomalies are also caused by the increase in solar radiation associated with the anticyclonic atmospheric Rossby wave over the EIO. Similarly, the physical processes of the summer warm events, which are followed by wintertime cold SST anomalies, can be explained by the changes in atmospheric and oceanic fields with opposite signs to those anomalies described above. 相似文献
20.
A nine-member ensemble of simulations with a state-of-the-art atmospheric model forced only by the observed record of sea
surface temperature (SST) over 1930–2000 is shown to capture the dominant patterns of variability of boreal summer African
rainfall. One pattern represents variability along the Gulf of Guinea, between the equator and 10°N. It connects rainfall
over Africa to the Atlantic marine Intertropical Convergence Zone, is controlled by local, i.e., eastern equatorial Atlantic,
SSTs, and is interannual in time scale. The other represents variability in the semi-arid Sahel, between 10°N and 20°N. It
is a continental pattern, capturing the essence of the African summer monsoon, while at the same time displaying high sensitivity
to SSTs in the global tropics. A land–atmosphere feedback associated with this pattern translates precipitation anomalies
into coherent surface temperature and evaporation anomalies, as highlighted by a simulation where soil moisture is held fixed
to climatology. As a consequence of such feedback, it is shown that the recent positive trend in surface temperature is consistent
with the ocean-forced negative trend in precipitation, without the need to invoke the direct effect of the observed increase
in anthropogenic greenhouse gases. We advance plausible mechanisms by which the balance between land–ocean temperature contrast
and moisture availability that defines the monsoon could have been altered in recent decades, resulting in persistent drought.
This discussion also serves to illustrate ways in which the monsoon may be perturbed, or may already have been perturbed,
by anthropogenic climate change. 相似文献