Cloud radiative kernels were built by BCC_RAD(Beijing Climate Center radiative transfer model)radiative transfer code.Then,short-term cloud feedback and its mechanisms in East Asia(0.5°S−60.5°N,69.5°−15...Cloud radiative kernels were built by BCC_RAD(Beijing Climate Center radiative transfer model)radiative transfer code.Then,short-term cloud feedback and its mechanisms in East Asia(0.5°S−60.5°N,69.5°−150.5°E)were analyzed quantitatively using the kernels combined with MODIS satellite data from July 2002 to June 2018.According to the surface and monsoon types,four subregions in East Asia-the Tibetan Plateau,northwest,temperate monsoon(TM),and subtropical monsoon(SM)—were selected.The average longwave,shortwave,and net cloud feedbacks in East Asia are−0.68±1.20,1.34±1.08,and 0.66±0.40 W m^−2 K^−1(±2σ),respectively,among which the net feedback is dominated by the positive shortwave feedback.Positive feedback in SM is the strongest of all subregions,mainly due to the contributions of nimbostratus and stratus.In East Asia,short-term feedback in spring is primarily caused by marine stratus in SM,in summer is primarily driven by deep convective cloud in TM,in autumn is mainly caused by land nimbostratus in SM,and in winter is mainly driven by land stratus in SM.Cloud feedback in East Asia is chiefly driven by decreases in mid-level and low cloud fraction owing to the changes in relative humidity,and a decrease in low cloud optical thickness due to the changes in cloud water content.展开更多
The cloud feedback on the SST variability in the western equatorial Pacific in GOALS/LASG model is studied in this paper. Two versions of the model, one with the diagnostic cloud and another with the prescribed cloud,...The cloud feedback on the SST variability in the western equatorial Pacific in GOALS/LASG model is studied in this paper. Two versions of the model, one with the diagnostic cloud and another with the prescribed cloud, are used. Both versions are integrated for 45 years. It is found that in the prescribed cloud run, the SST variability in the western equatorial Pacific is mainly of interdecadal time scale and the interannual variability is very weak. In the diagnostic cloud run, however, the interdecadal SST variability is depressed much and the interannual SST variability becomes much significant.The mechanism for the feedback is then explored. The variability of sea surface temperature (SST) in the western equatorial Pacific is found to be controlled mainly by the zonal wind anomaly, through the process of upwelling/downwelling in both versions. Then it is found that in the diagnostic cloud case, the negative feedback of the solar short wave (SW) flux acts significantly to balance the effect of upwelling/downwelling in addition to the latent flux. In addition, the variability of the SW flux is shown to be closely related to the variability of the middle and high cloud covers. Therefore, the negative feedback of the SW surface flux may have significant contribution to the cloud feedback on the SST variability.展开更多
A cloud-ocean planetary boundary layer (OPBL) feedback mechanism is presented and tested in this paper. Water vapor, evaporated from the ocean surface or transported by the large-scale air flow, often forms convective...A cloud-ocean planetary boundary layer (OPBL) feedback mechanism is presented and tested in this paper. Water vapor, evaporated from the ocean surface or transported by the large-scale air flow, often forms convective clouds under a conditionally unstable lapse rate. The variable cloud cover and rainfall may have positive and negative feedback with the ocean mixed layer temperature and salinity structure. The coupling of the simplified Kuo's (1965) cumulus cloud model to the Kraus-Turner's (1967) ocean mixed layer model shows the existence of this feedback mechanism. The theory also predicts the generation of low frequency oscillation in the atmosphere and oceans.展开更多
Cloud radiative kernels(CRK)built with radiative transfer models have been widely used to analyze the cloud radiative effect on top of atmosphere(TOA)fluxes,and it is expected that the CRKs would also be useful in the...Cloud radiative kernels(CRK)built with radiative transfer models have been widely used to analyze the cloud radiative effect on top of atmosphere(TOA)fluxes,and it is expected that the CRKs would also be useful in the analyses of surface radiative fluxes,which determines the regional surface temperature change and variability.In this study,CRKs at the surface and TOA were built using the Rapid Radiative Transfer Model(RRTM).Longwave cloud radiative effect(CRE)at the surface is primarily driven by cloud base properties,while TOA CRE is primarily decided by cloud top properties.For this reason,the standard version of surface CRK is a function of latitude,longitude,month,cloud optical thickness(τ)and cloud base pressure(CBP),and the TOA CRK is a function of latitude,longitude,month,τand cloud top pressure(CTP).Considering that the cloud property histograms provided by climate models are functions of CTP instead of CBP at present,the surface CRKs on CBP-τhistograms were converted to CTP-τfields using the statistical relationship between CTP,CBP andτobtained from collocated CloudSat and MODIS observations.For both climate model outputs and satellites observations,the climatology of surface CRE and cloud-induced surface radiative anomalies calculated with the surface CRKs and cloud property histograms are well correlated with those calculated from surface radiative fluxes.The cloud-induced surface radiative anomalies reproduced by surface CRKs and MODIS cloud property histograms are not affected by spurious trends that appear in Clouds and the Earth's Radiant Energy System(CERES)surface irradiances products.展开更多
Previous analyses on the estimates of water vapor and cloud-related feedbacks in the tropics usually use observations over the Earth Radiation Budget Experiment (ERBE) period (1985-89). To examine the sample dependenc...Previous analyses on the estimates of water vapor and cloud-related feedbacks in the tropics usually use observations over the Earth Radiation Budget Experiment (ERBE) period (1985-89). To examine the sample dependence of previous estimates, the authors extend the analysis to two additional periods: 1990-94 and 1995-99. The results confirm our hypothesis, i.e., the values of the feedbacks depend on the period of data coverage. The differences in the feedbacks from cloud radiative forcings (CRFs) estimated from the three periods are particularly significant. Two possible causes for these differences are proposed. First, a regime behavior in the CRFs-Sea Surface Temperature Anomaly (SSTA) relationship over the cold tongue region is revealed: when SSTA is below -0.5 C, the CRF anomalies are insensitive to the SSTA; when the SSTA is between -0.5 C and 2.0 C, the CRF anomalies are positively correlated with the SSTA; however, when the SSTA exceeds 2.0 C, the CRF anomalies decrease with the SSTA. This regime behavior is due to the regime behavior of cirrostratus and deep convective clouds. Second, the CRFs-SSTA relationship is regulated by remote forcings. Warming of the far eastern equatorial Pacific would reduce the water vapor convergence over the central Pacific by weakening the trade wind over the southeastern Pacific, thereby reducing the feeding of moisture to the convective flow. The results suggest that CRFs-SSTA relationships during ENSO events are nonlinear and strongly depend on the magnitude and the spatial distribution of the SSTA.展开更多
Coral reefs produce atmospheric dimethylsulfide (DMSa) which oxidises to non-sea-salt (nss) sulfate aerosols, precursors of cloud condensation nuclei (CCN) and low level cloud (LLC), reducing solar radiation and regul...Coral reefs produce atmospheric dimethylsulfide (DMSa) which oxidises to non-sea-salt (nss) sulfate aerosols, precursors of cloud condensation nuclei (CCN) and low level cloud (LLC), reducing solar radiation and regulating sea surface temperatures (SSTs). Here we report measurements of solar radiation, SST, LLC, DMS flux, , and rainfall before, during and after a major coral bleaching event at Magnetic Island in the central Great Barrier Reef (GBR). Measurements are compared with those made at the nearby fringing reef of Or-pheus Island where coral bleaching did not occur. Extreme solar radiation levels occurred from November to late January and could have reflected cloud radiative effects that increased downwelling of solar radiation. High levels of LLC often coincided with high periodic fluxes of DMS from the unbleached coral reef at Orpheus Island (e.g. 14 - 20 μmol·m-2·d-1), in direct contrast to the very low fluxes of DMS that were emitted from the bleached, human-impacted Magnetic Island fringing reef (nd-0.8 μmol·m-2·d-1) when SSTs were >30°C. Continuous SSTs measurements at the Magnetic Island reef revealed various heating and cooling periods, interspersed with stable SSTs. Cooling periods (negative climate feedback) ranged from -1°C to -3°C (7 day mean -1.6°C), and often seemed to occur during low tides, periodic pulses of DMS flux and LLC, keeping SSTs °C. In contrast warming periods of +1°C to +3°C (positive climate feedback, 7 day mean +1.52°C), seemed to occur during increasing tides, decreasing DMS flux and low to medium levels of LLC which increased solar radiation and caused SSTs over 30°C and corals to bleach. Alternation between these two states or types of feedback is indicated in this research and may be a function of enhanced scattering of solar radiation from nss-sulfate aerosols that originate from oxidation of DMSa produced from the coral reefs in the GBR. The net radiative forcing from clouds can be as high as four times as large as the radiative forcing from a doubling of CO2 levels in the atmosphere, which needs to be taken into account when ascribing coral bleaching events in the GBR solely to GHG warming. Further studies are needed to more critically assess the importance of this GBR coral reef-cloud feedback to the climate of northern Australia and the western Pacific, where the greatest biomass of coral reefs occurs.展开更多
基金supported by the National Key R&D Program of China(Grant No.2017YFA0603502)the National Natural Science Foundation of China(Grant Nos.91644211 and 41575002).
文摘Cloud radiative kernels were built by BCC_RAD(Beijing Climate Center radiative transfer model)radiative transfer code.Then,short-term cloud feedback and its mechanisms in East Asia(0.5°S−60.5°N,69.5°−150.5°E)were analyzed quantitatively using the kernels combined with MODIS satellite data from July 2002 to June 2018.According to the surface and monsoon types,four subregions in East Asia-the Tibetan Plateau,northwest,temperate monsoon(TM),and subtropical monsoon(SM)—were selected.The average longwave,shortwave,and net cloud feedbacks in East Asia are−0.68±1.20,1.34±1.08,and 0.66±0.40 W m^−2 K^−1(±2σ),respectively,among which the net feedback is dominated by the positive shortwave feedback.Positive feedback in SM is the strongest of all subregions,mainly due to the contributions of nimbostratus and stratus.In East Asia,short-term feedback in spring is primarily caused by marine stratus in SM,in summer is primarily driven by deep convective cloud in TM,in autumn is mainly caused by land nimbostratus in SM,and in winter is mainly driven by land stratus in SM.Cloud feedback in East Asia is chiefly driven by decreases in mid-level and low cloud fraction owing to the changes in relative humidity,and a decrease in low cloud optical thickness due to the changes in cloud water content.
文摘The cloud feedback on the SST variability in the western equatorial Pacific in GOALS/LASG model is studied in this paper. Two versions of the model, one with the diagnostic cloud and another with the prescribed cloud, are used. Both versions are integrated for 45 years. It is found that in the prescribed cloud run, the SST variability in the western equatorial Pacific is mainly of interdecadal time scale and the interannual variability is very weak. In the diagnostic cloud run, however, the interdecadal SST variability is depressed much and the interannual SST variability becomes much significant.The mechanism for the feedback is then explored. The variability of sea surface temperature (SST) in the western equatorial Pacific is found to be controlled mainly by the zonal wind anomaly, through the process of upwelling/downwelling in both versions. Then it is found that in the diagnostic cloud case, the negative feedback of the solar short wave (SW) flux acts significantly to balance the effect of upwelling/downwelling in addition to the latent flux. In addition, the variability of the SW flux is shown to be closely related to the variability of the middle and high cloud covers. Therefore, the negative feedback of the SW surface flux may have significant contribution to the cloud feedback on the SST variability.
文摘A cloud-ocean planetary boundary layer (OPBL) feedback mechanism is presented and tested in this paper. Water vapor, evaporated from the ocean surface or transported by the large-scale air flow, often forms convective clouds under a conditionally unstable lapse rate. The variable cloud cover and rainfall may have positive and negative feedback with the ocean mixed layer temperature and salinity structure. The coupling of the simplified Kuo's (1965) cumulus cloud model to the Kraus-Turner's (1967) ocean mixed layer model shows the existence of this feedback mechanism. The theory also predicts the generation of low frequency oscillation in the atmosphere and oceans.
基金supported by the National Natural Science Foundation of China(Grant No.NSFC 41875095,42075127).
文摘Cloud radiative kernels(CRK)built with radiative transfer models have been widely used to analyze the cloud radiative effect on top of atmosphere(TOA)fluxes,and it is expected that the CRKs would also be useful in the analyses of surface radiative fluxes,which determines the regional surface temperature change and variability.In this study,CRKs at the surface and TOA were built using the Rapid Radiative Transfer Model(RRTM).Longwave cloud radiative effect(CRE)at the surface is primarily driven by cloud base properties,while TOA CRE is primarily decided by cloud top properties.For this reason,the standard version of surface CRK is a function of latitude,longitude,month,cloud optical thickness(τ)and cloud base pressure(CBP),and the TOA CRK is a function of latitude,longitude,month,τand cloud top pressure(CTP).Considering that the cloud property histograms provided by climate models are functions of CTP instead of CBP at present,the surface CRKs on CBP-τhistograms were converted to CTP-τfields using the statistical relationship between CTP,CBP andτobtained from collocated CloudSat and MODIS observations.For both climate model outputs and satellites observations,the climatology of surface CRE and cloud-induced surface radiative anomalies calculated with the surface CRKs and cloud property histograms are well correlated with those calculated from surface radiative fluxes.The cloud-induced surface radiative anomalies reproduced by surface CRKs and MODIS cloud property histograms are not affected by spurious trends that appear in Clouds and the Earth's Radiant Energy System(CERES)surface irradiances products.
基金supported by the National Key Technologies R&D Program of China (2007BAC29B03)the National Natural Science Foundation of China (40890054 and 40821092)
文摘Previous analyses on the estimates of water vapor and cloud-related feedbacks in the tropics usually use observations over the Earth Radiation Budget Experiment (ERBE) period (1985-89). To examine the sample dependence of previous estimates, the authors extend the analysis to two additional periods: 1990-94 and 1995-99. The results confirm our hypothesis, i.e., the values of the feedbacks depend on the period of data coverage. The differences in the feedbacks from cloud radiative forcings (CRFs) estimated from the three periods are particularly significant. Two possible causes for these differences are proposed. First, a regime behavior in the CRFs-Sea Surface Temperature Anomaly (SSTA) relationship over the cold tongue region is revealed: when SSTA is below -0.5 C, the CRF anomalies are insensitive to the SSTA; when the SSTA is between -0.5 C and 2.0 C, the CRF anomalies are positively correlated with the SSTA; however, when the SSTA exceeds 2.0 C, the CRF anomalies decrease with the SSTA. This regime behavior is due to the regime behavior of cirrostratus and deep convective clouds. Second, the CRFs-SSTA relationship is regulated by remote forcings. Warming of the far eastern equatorial Pacific would reduce the water vapor convergence over the central Pacific by weakening the trade wind over the southeastern Pacific, thereby reducing the feeding of moisture to the convective flow. The results suggest that CRFs-SSTA relationships during ENSO events are nonlinear and strongly depend on the magnitude and the spatial distribution of the SSTA.
文摘Coral reefs produce atmospheric dimethylsulfide (DMSa) which oxidises to non-sea-salt (nss) sulfate aerosols, precursors of cloud condensation nuclei (CCN) and low level cloud (LLC), reducing solar radiation and regulating sea surface temperatures (SSTs). Here we report measurements of solar radiation, SST, LLC, DMS flux, , and rainfall before, during and after a major coral bleaching event at Magnetic Island in the central Great Barrier Reef (GBR). Measurements are compared with those made at the nearby fringing reef of Or-pheus Island where coral bleaching did not occur. Extreme solar radiation levels occurred from November to late January and could have reflected cloud radiative effects that increased downwelling of solar radiation. High levels of LLC often coincided with high periodic fluxes of DMS from the unbleached coral reef at Orpheus Island (e.g. 14 - 20 μmol·m-2·d-1), in direct contrast to the very low fluxes of DMS that were emitted from the bleached, human-impacted Magnetic Island fringing reef (nd-0.8 μmol·m-2·d-1) when SSTs were >30°C. Continuous SSTs measurements at the Magnetic Island reef revealed various heating and cooling periods, interspersed with stable SSTs. Cooling periods (negative climate feedback) ranged from -1°C to -3°C (7 day mean -1.6°C), and often seemed to occur during low tides, periodic pulses of DMS flux and LLC, keeping SSTs °C. In contrast warming periods of +1°C to +3°C (positive climate feedback, 7 day mean +1.52°C), seemed to occur during increasing tides, decreasing DMS flux and low to medium levels of LLC which increased solar radiation and caused SSTs over 30°C and corals to bleach. Alternation between these two states or types of feedback is indicated in this research and may be a function of enhanced scattering of solar radiation from nss-sulfate aerosols that originate from oxidation of DMSa produced from the coral reefs in the GBR. The net radiative forcing from clouds can be as high as four times as large as the radiative forcing from a doubling of CO2 levels in the atmosphere, which needs to be taken into account when ascribing coral bleaching events in the GBR solely to GHG warming. Further studies are needed to more critically assess the importance of this GBR coral reef-cloud feedback to the climate of northern Australia and the western Pacific, where the greatest biomass of coral reefs occurs.