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1.
The impact of contrail-induced cirrus clouds on regional climate is estimated for mean atmospheric conditions of southern Germany in the months of July and October. This is done by use of a regionalized one-dimensional radiative convective model (RCM). The influence of an increased ice cloud cover is studied by comparing RCM results representing climatological values with a modified case. In order to study the sensitivity of this effect on the radiative characteristics of the ice cloud, two types of additional ice clouds were modelled: cirrus and contrails, the latter cloud type containing a higher number of smaller and less of the larger cloud particles. Ice cloud parameters are calculated on the basis of a particle size distribution which covers the range from 2 to 2000 m, taking into consideration recent measurements which show a remarkable amount of particles smaller than 20 m. It turns out that a 10% increase in ice cloud cover leads to a surface temperature increase in the order of 1K, ranging from 1.1 to 1.2K in July and from 0.8 to 0.9K in October depending on the radiative characteristics of the air-traffic-induced ice clouds. Modelling the current contrail cloud cover which is near 0.5% over Europe yields a surface temperature increase in the order of 0.05 K.  相似文献   

2.
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3.
Air traffic is a source of trace gases in the upper troposphere and lower stratosphere. Contrails readily form from water vapor exhausts under favorable meteorological conditions. Since contrails are ice crystal clouds like natural cirrus clouds, they bear a greenhouse potential which has to be investigated. The IFU has built a scanning lidar system employing a pulsed Nd:YAG laser as the emitter and a 52-cm diameter telescope as the receiver. Signals are processed in several channels to investigate depolarization and wavelength dependencies of the light backscattered from ice crystals. These investigations are aimed at the formation and life cycles of contrails, their optical properties, and their climatological consequences in areas of dense air traffic. The experimental lidar setup is described and a sample measurement is shown.  相似文献   

4.
The warming over the Tibetan Plateau(TP) is very significant during last 30 years,but the thermal forcing has been weakened.The thermal weakening is attributed mainly to the enhancement of the TOA(top of atmosphere) outgoing radiation.This enhancement is opposite to the greenhouse-gas-induced weakening of the global mean TOA outgoing radiation and is also unable to be explained by the observed decrease of total cloud cover.This study presents the importance of cloud height change and the warming over the TP in modulating the TOA radiation budget and thus the thermal forcing during spring and summer.On the basis of surface observations and satellite radiation data,we found that both the TOA outgoing shortwave radiation and longwave radiation were enhanced during this period.The former enhancement is due mainly to the increase of low-level cloud cover,which has a strong reflection to shortwave radiation,especially in summer.The latter enhancement is caused mainly by the planetary warming,and it is further enhanced by the decrease of total cloud cover in spring,as clouds extinguish outgoing longwave radiation emitted from the land surface.Therefore,the radiative cooling enhancement and thus the thermal weakening over the TP is a response of the earth-atmosphere system to the unique change of cloud cover configuration and the rapid warming of the land surface.However,these trends in cloud cover and TOA outgoing radiation are not well represented in four reanalyses.  相似文献   

5.
Contrail frequency over Europe from NOAA-satellite images   总被引：1，自引：0，他引：1  
Contrail cloudiness over Europe and the eastern part of the North Atlantic Ocean was analyzed for the two periods September 1979 - December 1981 and September 1989 - August 1992 by visual inspection of quicklook photographic prints of NOAA/AVHRR infrared images. The averaged contrail cover exhibits maximum values along the transatlantic flight corridor around 50 °N (of almost 2%) and over western Europe resulting in 0.5% contrail cloudiness on average. A strong yearly cycle appears with a maximum (<2%) in spring and summer over the Atlantic and a smaller maximum (<1%) in winter over southwestern Europe. Comparing the two time periods, which are separated by one decade, shows there is a significant decrease in contrail cloudiness over western Europe and a significant increase over the North Atlantic between March and July. Contrail cloud cover during daytime is about twice as high as during nighttime. Contrails are found preferentially in larger fields of 1000 km diameter which usually last for more than a day. Causes, possible errors and consequences are discussed.  相似文献   

6.
A one-dimensional spectral infrared radiative transfer model has been developed for atmospheres containing cirrus clouds and absorbing gases above, below and within the cloud. The transfer model takes into consideration the inhomogeneity of the cloudy atmosphere, the gaseous absorption in scattering cloud layers and the wavenumber dependence of radiative transfer. In addition, the cirrus cloud is further divided into a number of sub-layers to account for the non-isothermal and inhomogeneous cloud characteristics. Single-scattering properties for ice crystals are calculated assuming ice cylinders 200 and 60 m in lenght and width, respectively, randomly oriented in a horizontal plane. The spectral infrared transfer program is applied to VTPR channels of the NOAA 4 satellite to simulate upward radiances in cirrus cloud conditions.Comparisons between satellite observed and theoretically simulated upward radiances are carried out for selected cirrus cloud cases. Incorporating atmospheric profiles obtained from radiosonde and the observed cloud information into the spectral transfer program, we show a systematic agreement between observed and computed upward radiances. Systematic reduction patterns of the upward radiance caused by the increase of the cloud ice content are clearly demonstrated for VTPR channels employing tropical and midlatitude atmospheric profiles. Having the quantitative relationships between upward radiances and ice contents, procedures are described for the inference of the cloud ice content and cloud amount. The proposed method has been successfully applied to the three cirrus cloud cases.  相似文献   

7.
We have examined long-term changes in Earth’s energy flows at top of the atmosphere (TOA) and at Earth’s surface (land and ocean) by using 228-year simulation of a high-resolution global atmosphere model, MRI-AGCM3.2. It is found that the net downward short wave (SW) radiation (absorbed solar radiation, ASR) at TOA significantly increases during twenty-first century in agreement with a previous study. However, in the present study, the reason for the change is an increase in clear sky SW absorption by increased water vapor in the atmosphere, while it is a decrease in cloud amount in the previous study. It is also found that the long wave (LW) cloud radiative forcing for atmosphere is positive and increasing during twenty-first century in agreement with a previous study. The reason for the change in the present study is an increase in absorption by water vapor of the downward LW radiation emitted from clouds, while it is reductions of cloud amount in the middle troposphere in the previous study.  相似文献   

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9.
Using the National Center for Atmospheric Research (NCAR) general circulation model (CCM2), a suite of alternative cloud radiation parameterizations has been tested. Our methodology relies on perpetual July integrations driven by ±2 K sea surface temperature forcing. The tested parameterizations include relative humidity based clouds and versions of schemes involving a prognostic cloud water budget. We are especially interested in testing the effect of cloud optical thickness feedbacks on global climate sensitivity. All schemes exhibit negative cloud radiation feedbacks, i.e., cloud moderates the global warming. However, these negative net cloud radiation feedbacks consist of quite different shortwave and longwave components between a scheme with interactive cloud radiative properties and several schemes with specified cloud water paths. An increase in cloud water content in the warmer climate leads to optically thicker middle- and low-level clouds and in turn negative shortwave feedbacks for the interactive radiative scheme, while a decrease in cloud amount leads to a positive shortwave feedback for the other schemes. For the longwave feedbacks, a decrease in high effective cloudiness for the schemes without interactive radiative properties leads to a negative feedback, while no distinct changes in effective high cloudiness and the resulting feedback are exhibited for the scheme with interactive radiative properties. The resulting magnitude of negative net cloud radiation feed-back is largest for the scheme with interactive radiative properties. Even though the simulated values of cloud radiative forcing for the present climate using this method differ most from the observational data, the approach shows great promise for the future.  相似文献   

10.
We compare the equilibrium climate responses of a quasi-dynamical energy balance model to radiative forcing by equivalent changes in CO2, solar total irradiance (Stot) and solar UV (SUV). The response is largest in the SUV case, in which the imposed UV radiative forcing is preferentially absorbed in the layer above 250 mb, in contrast to the weak response from global-columnar radiative loading by increases in CO2 or Stot. The hypersensitive response of the climate system to solar UV forcing is caused by strongly coupled feedback involving vertical static stability, tropical thick cirrus ice clouds and stratospheric ozone. This mechanism offers a plausible explanation of the apparent hypersensitivity of climate to solar forcing, as suggested by analyses of recent climatic records. The model hypersensitivity strongly depends on climate parameters, especially cloud radiative properties, but is effective for arguably realistic values of these parameters. The proposed solar forcing mechanism should be further confirmed using other models (e.g., general circulation models) that may better capture radiative and dynamical couplings of the troposphere and stratosphere.  相似文献   

11.
Ice crystal clouds have an influence on the radiative budget of the earth; however, the exact size and nature of this influence has yet to be determined. A laboratory cloud chamber experiment has been set up to provide data on the optical scattering behaviour of ice crystals at a visible wavelength in order to gain information which can be used in climate models concerning the radiative characteristics of cirrus clouds. A PMS grey-scale probe is used to monitor simultaneously the cloud microphysical properties in order to correlate these closely with the observed radiative properties. Preliminary results show that ice crystals scatter considerably more at 90° than do water droplets, and that the halo effects are visible in a laboratorygenerated cloud when the ice crystal concentration is sufficiently small to prevent masking from multiple scattering.  相似文献   

12.
Projections of future climate change by climate system models depend on the sensitivities of models to specified greenhouse gases.To reveal and understand the different climate sensitivities of two versions of LASG/IAP climate system model FGOALS-g2 and FGOALS-s2,we investigate the global mean surface air temperature responses to idealized CO2 forcing by using the output of abruptly quadrupling CO2 experiments.The Gregory-style regression method is used to estimate the"radiative forcing"of quadrupled CO2 and equilibrium sensitivity.The model response is separated into a fast-response stage associated with the CO2 forcing during the first 20 years,and a slow-response stage post the first 20 years.The results show that the radiative forcing of CO2 is overestimated due to the positive water-vapor feedback and underestimated due to the fast cloud processes.The rapid response of water vapor in FGOALS-s2 is responsible for the stronger radiative forcing of CO2.The climate sensitivity,defined as the equilibrium temperature change under doubled CO2 forcing,is about 3.7 K in FGOALS-g2 and4.5 K in FGOALS-s2.The larger sensitivity of FGOALS-s2 is due mainly to the weaker negative longwave clear-sky feedback and stronger positive shortwave clear-sky feedback at the fast-response stage,because of the more rapid response of water vapor increase and sea-ice decrease in FGOALS-s2 than in FGOALS-g2.At the slow-response stage,similar to the fast-response stage,net negative clear-sky feedback is weaker in FGOALS-s2.Nevertheless,the total negative feedback is larger in FGOALS-s2 due to a larger negative shortwave cloud feedback that involves a larger response of total cloud fraction and condensed water path increase.The uncertainties of estimated forcing and net feedback mainly come from the shortwave cloud processes.  相似文献   

13.
We examine the impact of the Atmospheric Brown Clouds on the direct radiative forcing of the Himalayan foothills and the Indo-Gangetic Plains (IGP) regions, home for over 500 million S. Asians. The NASA-Terra MODIS satellite data reveal an extensive layer of aerosols covering the entire IGP and Himalayan foothills region with seasonal mean AODs of about 0.4 to 0.5 in the visible wavelengths (0.55 micron), which fall among the largest seasonal mean dry season AODs for the tropics. We show new surface data which reveal the presence of strongly absorbing aerosols that lead to a large reduction in solar radiation fluxes at the surface during the October to May period. The three-year mean (2001 to 2003) October to May seasonal and diurnal average reduction in surface solar radiation for the IGP region is about 32 (±5) W m−2 (about 10% of TOA insolation or 20% of surface insolation). The forcing efficiency (forcing per unit optical depth) is as large as −27% (note that the forcing is negative) of top-of-atmosphere (TOA) solar insolation, and exceeds the forcing efficiency that has been observed for other polluted regions in America, Africa, East Asia, and Europe. General circulation model sensitivity studies suggest that both the local and remote influence of the aerosol induced radiative forcing is to strengthen the lower atmosphere inversion, stabilize the boundary layer, amplify the climatological tendency for a drier troposphere, and decrease evaporation. These aerosol-induced changes could potentially increase the life times of aerosols, make them more persistent, and decrease their single scattering albedos, thus potentially leading to a detrimental positive feedback between aerosol concentrations, aerosol forcing, and aerosol persistence. In addition, both the model studies and observations of pan evaporation suggest that the reduction in surface solar radiation may have led to a reduction in surface evaporation of moisture. These results suggest the vulnerability of this vital region to air pollution related direct and indirect (through climate changes) impacts on agricultural productivity of the region.  相似文献   

14.
Air temperature feedback results from the thermal-radiative coupling between the atmosphere and the surface and plays an important role in surface energy balance. This paper reveals the contribution of air temperature feedback to the global warming from 1980 to 2000. The air temperature feedback kernel, evaluated using the ERA-Interim reanalysis data, is used to discuss the physical mechanism for air temperature feedback, the dependency of the strength of air temperature feedback on the climatological spatial distributions of air temperature, water vapor and cloud content, and the contributions of air temperature feedback to rapid global warming. The coupling between temperature feedback and each of the external forcings and individual feedback processes will amplify the anomaly of direct energy flux convergence at the surface induced by the external forcings and individual processes. The air temperature feedback amplifies the initial surface warming due to the increase in CO2 concentration, ice and snow melting, increase in water vapor, and change in ocean heat storage. It also amplifies the surface warming due to the longwave radiaitve forcing associated with the increase in cloud cover, which acts to suppress the cooling of the shortwave effect of cloud forcing. Overall, temperature feedback plays an important role in the global warming from 1980 to 2000, as the net positive contribution to the perturbation of global mean energy flux at the surface from the air temperature feedback is larger than the net negative contribution from external forcing and all non-temperature feedbacks.  相似文献   

15.
With a radiative transfer model, assessments are made of the radiative forcing in northern mid-latitudes due to aircraft emissions up to 1990. Considered are the direct climate effects from the major combustion products carbon dioxide, nitrogen dioxide, water vapor and sulphur dioxide, as well as the indirect effect of ozone production from NOx emissions. Our study indicates a local radiative forcing at the tropopause which should be negative in summer (-0.5 to 0.0 W/m2) and either negative or positive in winter (-0.3 to 0.2 W/m2). To these values the indirect effect of contrails has to be added, which for the North Atlantic Flight Corridor covers the range -0.2 to 0.3 W/m2 in summer and 0.0 to 0.3 W/m2 in winter. Apart from optically dense non-aged contrails during summer, negative forcings are due to solar screening by sulphate aerosols. The major positive contributions come from contrails, stratospheric water vapor in winter and ozone in summer. The direct effect of NO2 is negligible and the contribution of CO2 is relatively small.  相似文献   

16.
Observations taken by aircraft and conventional platforms are used to investigate dynamical, physical, and radiative processes within a marine stratus cloud during the Canadian Atlantic Storms Program (CASP) II field project which took place over the east coast of Canada. Stratus which formed over the ocean on February 6, 1992 during the nighttime, is studied to analyze cloud top and base processes. The cloud was supercooled during the study period. Fluctuations and fluxes are calculated along constant flight altitude legs approximately 100 km long in space. The scales of structures larger than 5 km are removed from the analysis using a running average technique. Droplet spectra obtained by a forward scattering spectrometer probe (FSSP) were used in a 1-D radiative transfer model to calculate infrared (IR) fluxes and radiative heating rates. A heat conservation equation was used to estimate vertical air velocity (w a ) within the cloud. The results showed that, because of a warmer ocean surface, significant moisture and heat were transferred from the ocean surface to the boundary layer. The cloud base was at about 400 m height and the top was at about 1.4 km.w a at the cloud base was estimated about 5 cm s–1. Strong IR cooling rate at the cloud top was calculated to be 75°C day–1 for a 100 m thick layer. Negative skewness inw a , suggesting narrow downdrafts, was likely due to radiative cooling at the cloud top. The entrainment velocity was found to be about 1.5 cm s–1 at cloud top. Mean moisture and heat fluxes within the cloud were estimated to be comparable to those from the ocean surface. Vertical air velocity at the cloud top due to radiative cooling was found to be about –40 cm s–1.  相似文献   

17.
Radiative properties of cirrus clouds are one of the major unsolved problems in climate studies and global radiation budget. These clouds are generally composed of various ice-crystal shapes, so we tried to evaluate effects of the ice-crystal shape on radiative fluxes. We calculated radiative fluxes of cirrus clouds with a constant geometrical depth, composed of ice crystals with different shapes (hexagonal columns, bullets, bullet-rosettes), sizes and various concentrations. We considered ice particles randomly oriented in space (3D case) and their scattering phase functions were calculated by a ray-tracing method. We calculated radiative fluxes for cirrus layers for different microphysical characteristics by using a discrete-ordinate radiative code. Results showed that the foremost effect of the ice-crystal shape on radiative properties of cirrus clouds was that on the optical thickness, while the variation of the scattering phase function with the ice shape remained less than 3% for our computations. The ice-water content may be a better choice to parameterize the optical properties of cirrus, but the shape effect must be included.  相似文献   

18.
本文利用大气环流模式及大气化学模式所得气溶胶资料,估算了相对1850s时期硫酸盐和黑碳气溶胶引起的全球及东亚区域人为辐射强迫,重点分析其在东亚区域的季节和长期变化特征.结果表明,就当前全球年平均全天空而言,人为硫酸盐气溶胶对大气顶的直接和云反照率强迫分别为-0.37和-0.98 W·m-2,黑碳气溶胶对大气顶和整层大气的辐射强迫值为0.16和0.47 W·m-2;中国东部区域是目前上述气溶胶辐射强迫最强的区域,硫酸盐的直接和间接辐射强迫分别超过-2.0和-4.0 W·m-2,黑碳对大气顶和整层大气的直接辐射强迫分别可达2.0和5.0W·m-2;估算的东亚区域上述气溶胶辐射强迫仍在不断增强,峰值预计出现在2010s时段,而且中国东部较强的辐射强迫还可能维持至2030s左右;在未来中、高排放情景下,东亚区域以上两种气溶胶预计对全球气溶胶辐射强迫有更大的贡献.分析还表明,夏季东亚区域较强的水汽会增强吸湿性硫酸盐气溶胶的光学厚度和晴空直接辐射强迫;云的作用一方面会强化东亚区域全天空条件下大气顶黑碳的辐射强迫,另一方面会影响硫酸盐气溶胶间接云反照率强迫的季节变化;上述气候特征的差异使得东亚区域的气溶胶辐射强迫表现出与欧美区域有所不同的特征.本文所用的气溶胶资料与模式气象场的偏差会给气溶胶辐射强迫计算带来一些不确定性,进一步改进气候模式中气溶胶过程、水汽和云等气象场的模拟将有助于获得更为合理的区域气溶胶辐射强迫估算结果.  相似文献   

19.
Biases in shortwave cloud radiative forcing (SWCF), which cause overestimates in tropical regions and underestimates in subtropical marine stratocumulus regions, are common in many climate models. Here, two boundary layer processes are investigated in the atmospheric model GAMIL2, entrainment at the top of the boundary layer and longwave radiative cooling at the top of stratocumulus clouds, in order to reduce biases and reveal the mechanisms underlying these processes. Our results show that including the entrainment process in the model can reduce negative SWCF biases in most tropical regions but increases positive SWCF biases in subtropical marine stratocumulus regions. This occurs because entrainment reduces the low-level cloud fraction and its cloud liquid water content by suppressing the vertical turbulent diffusion in the boundary layer and decreasing the relative humidity when warm and dry free atmosphere is entrained in the boundary layer. Longwave radiative cooling at the top of stratocumulus clouds can enhance turbulent diffusion within the stratocumulus-topped boundary layer. When combined with the entrainment process, longwave radiative cooling reduces the positive SWCF biases in subtropical marine stratocumulus regions that are observed using the entrainment process alone. The incorporation of these two boundary layer processes improves the simulated SWCF in tropical and subtropical regions in GAMIL2.  相似文献   

20.
A theoretical model based on some physical assumptions has been integrated to study the scattering of solar radiation by aerosol particulates of any size present in the atmosphere. Using this model, which incorporates multiple scattering, scattered fluxes of radiation with varying optical depths and also the optical depth versus wavelengths are computed. The present results are found to be in close agreement with the observations of the Pre-Indian Ocean Experiment (INDOEX) 1996. This provides evidence of the direct effect of aerosol particulates on the radiative forcing of the atmosphere.  相似文献   

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