A Quasi-Linear Relationship between Planetary Outgoing Longwave Radiation and Surface Temperature in a Radiative-Convective-Transportive Climate Model of a Gray Atmosphere

In this study,we put forward a radiative-convective-transportive energy balance model of a gray atmosphere to examine individual roles of the greenhouse effect of water vapor,vertical convection,and atmospheric poleward energy transport as well as their combined effects for a quasi-linear relationship between the outgoing longwave radiation(OLR)and surface temperature(T_(S)).The greenhouse effect of water vapor enhances the meridional gradient of surface temperature,thereby directly contributing to a quasi-linear OLR-T_(S) relationship.The atmospheric poleward energy transport decreases the meridional gradient of surface temperature.As a result of the poleward energy transport,tropical(high-latitude)atmosphere-surface columns emit less(more)OLR than the solar energy input at their respective locations,causing a substantial reduction of the meridional gradient of the OLR.The combined effect of reducing the meridional gradients of both OLR and surface temperature by the poleward energy transport also contributes to the quasi-linear OLR-T_(S) relationship.Vertical convective energy transport reduces the meridional gradient of surface temperature without affecting the meridional gradient of OLR,thereby suppressing part of the reduction to the increasing rate of OLR with surface temperature by the greenhouse effect of water vapor and poleward energy transport.Because of the nature of the energy balance in the climate system,such a quasi-linear relationship is also a good approximation for the relationship between the annual-mean net downward solar energy flux at the top of the atmosphere and surface temperature.

Correlation Analysis of Persistent Heavy Rainfall Events in the Vicinity of the Yangtze River Valley and Global Outgoing Longwave Radiation in the Preceding Month

Based on the National Oceanic and Atmospheric Administration （NOAA） daily satellite dataset of global outgoing longwave radiation （OLR） for the period of 1974-2004 and the NCEP-NCAR reanalysis for 1971- 2004, the linkage between persistent heavy rainfall （PHR） events in the vicinity of the Yangtze River valley and global OLR leading up to those events （with 1- to 3O-day lag） was investigated. The results reveal that there is a significant connection between the initiation of PHR events over the study area and anomalous convective activity over the tropical Indian Ocean, maritime continent, and tropical western Pacific Ocean. During the 30-day period prior to the onset of PHR events, the major significantly anomalous convective centers have an apparent dipole structure, always with enhanced convection in the west and suppressed convection in the east. This dipole structure continuously shifts eastward with time during the 30-day lead period. The influence of the anomalous convective activity over the tropical oceans on the initiation of PHR events over the study area is achieved via an interaction between tropical and extratropical latitudes. More specifically, anomalous convective activity weakens the Walker circulation cell over the tropical Indian Ocean first. This is followed by a weakening of the Indian summer monsoon background state and the excitation and dispersion of Rossby wave activity over Eurasia. Finally, a major modulation of the large scale background circulation occurs. As a result, the condition of a phase-lock among major large scale circulation features favoring PHR events is established over the study area.

Retrieval of Outgoing Longwave Radiation from COMS Narrowband Infrared Imagery

Hourly outgoing longwave radiation （OLR） from the geostationary satellite Communication Oceanography Meteorological Satellite （COMS） has been retrieved since June 2010.The COMS OLR retrieval algorithms are based on regression analyses of radiative transfer simulations for spectral functions of COMS infrared channels.This study documents the accuracies of OLRs for future climate applications by making an intercomparison of four OLRs from one single-channel algorithm （OLR12.0 using the 12.0 μm channel） and three multiple-channel algorithms （OLR10.8＋12.0 using the 10.8 and 12.0 pm channels; OLR6.7＋10.8 using the 6.7 and 10.8 μm channels; and OLRAll using the 6.7,10.8,and 12.0 μm channels）.The COMS OLRs from these algorithms were validated with direct measurements of OLR from a broadband radiometer of the Clouds and Earth＇s Radiant Energy System （CERES） over the full COMS field of view [roughly （50°S-50°N,70°-170°E）] during April 2011.Validation results show that the root-mean-square errors of COMS OLRs are 5-7 W m-2,which indicates good agreement with CERES OLR over the vast domain.OLR6.7＋10.8 and OLRAll have much smaller errors （～ 6 W m-2） than OLR12.0 and OLR10.8＋12.0 （～ 8 W m-2）.Moreover,the small errors of OLR6.7＋10.8 and OLRAll are systematic and can be readily reduced through additional mean bias correction and/or radiance calibration.These results indicate a noteworthy role of the 6.7 μm water vapor absorption channel in improving the accuracy of the OLRs.The dependence of the accuracy of COMS OLRs on various surface,atmospheric,and observational conditions is also discussed.

Generation of global 1-km daily top-of-atmosphere outgoing longwave radiation product from 2000 to 2021 using machine learning

Top-of-atmosphere(TOA)outgoing longwave radiation(OLR),a key component of the Earth’s energy budget,serves as a diagnostic of the Earth’s climate system response to incoming solar radiation.However,existing products are typically estimated using broadband sensors with coarse spatial resolutions.This paper presents a machine learning method to estimate TOA OLR by directly linking Moderate Resolution Imaging Spectroradiometer(MODIS)TOA radiances with TOA OLR determined by Clouds and the Earth’s Radiant Energy System(CERES)and other information,such as the viewing geometry,land surface temperature and cloud top temperature determined by Modern-Era Retrospective analysis for Research and Applications,Version 2(MERRA-2).Models are built separately under clear-and cloudy-sky conditions using a gradient boosting regression tree.Independent test results show that the root mean square errors(RMSEs)of the clear-sky and cloudy-sky models for estimating instantaneous values are 4.1 and 7.8 W/m^(2),respectively.Real-time conversion ratios derived from CERES daily and hourly OLR data are used to convert the instantaneous MODIS OLR to daily results.Inter-comparisons of the daily results show that the RMSE of the estimated MODIS OLR is 8.9 W/m^(2) in East Asia.The developed high resolution dataset will be beneficial in analyzing the regional energy budget.

ADVANCES IN APPLIED RESEARCH OF THE OUTGOING LONGWAVE RADIATION IN CHINA

The outgoing longwave radiation(OLR)observed by NOAA satellite series has widely applied in various research fields since the 1980s in China.In this paper,advances of the applied research of OLR are described in the following re- spects: (1)Studies of the global ITCZ; (2)Climatology of the subtropical high over northern Pacific; (3)Studies of the tropical cyclone over West Pacific; (4)Characteristics of the intraseasonal variation(ISV)of tropical convective activities; (5)Divergence wind and large scale circulation over the tropics; (6)Studies of the air-sea interaction; (7)Estimation of precipitation over the Tibetan Plateau and the Yangtze River(Changjiang River)basin during the rainy season; (8)Analyses of regional climates of China; (9)Studies of prediction of the severe and disastrous weather and climate; (10)Atlas of OLR. The distinctive features of these advances are reviewed and the focal points of the OLR applied research in future are also suggested.

CLIMATIC CHARACTERISTICS OF EARTH-ATMOSPHERE OUTGOING LONGWAVE RADIATION OVER CHINA

ERBE and ISCCP data are used to investigate the cloud forcing and latitude and atmospheric temperature effects on outgoing longwave radiation(OLR)in the earth-atmosphere system,and the similarity of OLR field to 500 hPa and surface effective radiation fields.Also,discussion is taken up of the OLR distribution on a nationwide basis,indicating that the winter(summer)OLR pattern is roughly a zonal type(asymmetrical saddle)with the annual pattern analogous to the January one.In the end the yearly OLR variation features are addressed on a regional basis.

INVESTIGATION OF LAGGED CORRELATION BETWEEN THE TEMPERATURE OF CHINA AND THE GLOBAL OUTGOING LONGWAVE RADIATION IN 1974-1985

1-12 month lagged correlations between winter temperatures at 22 stations in China and the global dis- tribution of the Outgoing Longwave Radiation(OLR)are investigated.The basic results are:(1)The monthly averaged temperatures of Dec.,Jan.and Feb.of China are correlated to the global distribution of OLR of Oct.,Nov.and Dec.,respectively.It is consistent with the response period(about 50 days)of 500 hPa geopotential height field in extratropical latitudes to the thermal forcing in tropical latitudes,and also consis- tent with the Walker cell of a 40-60 day oscillation.(2)There is a significant positive correlation between the winter temperature of the most part of China and the OLR in the Gulf of Mexico.It shows that when the thermal forcing of the Gulf of Mexico is stronger,the excited barotropic instability of westerlies in northern Atlantic could influence the East Asian circulation and cause the temperature of China to be below normal. (3)The temperature around the Tibetan(Xizang)Plateau is negatively correlated to the OLR in western equa- torial Pacific,showing that when the Walker cell is stronger,the local Hadley cell in Southeast Asia is stronger and it causes the temperature around the Tibetan Plateau to be higher than normal.

Evaluation of Reprocessed Fengyun-3B Global Outgoing Longwave Radiation Data:Comparison with CERES OLR

Outgoing longwave radiation(OLR)at the top of the atmosphere(TOA)is a key parameter for understanding and interpreting the relationship between clouds,radiation,and climate interactions.It has been one of the operational products of the Fengyun(FY)meteorological satellites.OLR accuracy has gradually improved with advancements in satellite payload performance and the OLR retrieval algorithm.Supported by the National Key R&D Program Retrospective Calibration of Historical Chinese Earth Observation Satellite data(Richceos)project,a long-term OLR climate data record(CDR)was reprocessed based on the recalibrated Level 1 data of FY series satellites using the latest OLR retrieval algorithm.In this study,Fengyun-3B(FY-3B)’s reprocessed global OLR data from 2010 to 2018 were evaluated by using the Clouds and the Earth’s Radiant Energy System(CERES)global daily OLR data.The results showed that there was a high consistency between the FY-3B instantaneous OLR and CERES Single Scanner Footprint(SSF)OLR.Globally,between the two CDR datasets,the correlation coefficient reached 0.98,and the rootmean-square error(RMSE)was approximately 8-9 W m^(−2).The bias mainly came from the edge regions of the satellite orbit,which may be related to the satellite zenith angle and cloud cover distribution.It was shown that the longterm FY-3B OLR had temporal stability compared to CERES OLR long-term data.In terms of spatial distribution,the mean deviations showed zonal and seasonal characteristics,although seasonal fluctuations were observed in the differences between the two datasets.Effects of FY-3B OLR application to the South China Sea monsoon region and ENSO were demonstrated and analyzed,and the results showed that the seasonal deviation of FY-3B’s OLR comes mainly from the retrieval algorithm.However,it has little effect on the analysis of climate events.

Observational Evidence for Poleward Expansion of the Hadley Circulation

How the Hadley circulation changes in response to global climate change and how its change impacts upon regional and global climates has generated a lot of interest in the literature in the past few years. In this paper, consistent and statistically significant poleward expansion of the Hadley circulation in the past few decades is demonstrated, using independent observational datasets as proxy measures of the Hadley circulation. Both observational outgoing longwave radiation and precipitation datasets show an annual average total poleward expansion of the Hadley cells of about 3.6° latitude. Sea level pressure from observational and reanalysis datasets show smaller magnitudes of poleward expansion, of about 1.2° latitude. Ensemble general circulation model simulations forced by observed time-varying sea surface temperatures were found to generate a total poleward expansion of about 1.23°latitude. Possible mechanisms behind the changes in the horizontal extent of the Hadley circulation are discussed.

Improved interpolation method based on singular spectrum analysis iteration and its application to missing data recovery

A novel interval quartering algorithm （IQA） is proposed to overcome insufficiency of the conventional singular spectrum analysis （SSA） iterative interpolation for selecting parameters including the number of the principal components and the embedding dimension. Based on the improved SSA iterative interpolation, interpolated test and comparative analysis are carried out to the outgoing longwave radiation daily data. The results show that IQA can find globally optimal parameters to the error curve with local oscillation, and has advantage of fast computing speed. The improved interpolation method is effective in the interpolation of missing data.

SEASONAL DEPENDENCE OF LOCAL AIR-SEA INTERACTION OVER THE TROPICAL WESTERN PACIFIC WARM POOL

Based on the air-sea interface heat fluxes and related meteorological variables datasets recently released by Objectively Analyzed Air-Sea Fluxes(OA Flux) Project of Woods Hole Oceanographic Institution,as well as the outgoing longwave radiation and surface wind datasets from National Oceanic and Atmospheric Administration,the seasonal dependence of local air-sea interaction over the tropical western Pacific warm pool(referred to the region(1o-6oN,144o-154oE)) is revealed and the probable impacts of remote forcing on the air-sea interaction are examined.The results indicated the dominance of oceanic forcing with the significant impact of ENSO in March and that of atmospheric feedback without notable influence of remote forcing in June.While the interannual variability of sea surface temperature anomaly(SSTA) is larger than that of SSTA tendency when oceanic forcing is dominant,the opposite is true when atmospheric feedback is dominant.The magnitude of the oceanic forcing of the atmosphere tends to decrease in March with the occurrence of ENSO,though ENSO has little influence on the atmospheric feedback to the ocean in June.The local air-sea interaction is substantially the same before and after the removal of the effect of Indian Oceanic Dipole.The reduction of shortwave radiation fluxes into the western Pacific warm pool,due to the enhanced overlaying convection in March associated with ENSO,leads to the decline of SST tendency that will weaken the oceanic forcing of the atmosphere.

AN INVESTIGATION INTO TROPICAL CYCLONE MOVING DIRECTION PREDICTION BASED ON OLR DATA

An objective technique of tropical cyclone （TC） moving direction prediction over the Northwestern Pacific Ocean during 2001 - 2002 is studied using GMS-50uting-Longwave Radiation （OLR）data. Three formulae used to predict TC moving direction in 6, 12 and 24 h, respectively, have been obtained based on a multiple linear regression framework and some regression factors including several kinds of OLR characteristic values and the minimum sea level pressure of tropical cyclone center. The multiple correlation coefficients of the statistical analysis using the information of TCs in the Yearbook on Tropical Cyclones to validate the satellite-based prediction are 0.954, 0.945 and 0.914 respectively. The results are satisfying through checking one of the TCs in 2001.The techniques could be applied in future operation and would contribute to TC movement prediction, especially to a sudden change in TC moving direction and improving the forecasting and warning capability.

Atmospheric insight to climatic signals of δ^18O in a Laohugou ice core in the northeastern Tibetan Plateau during 1960–2006

Ice documentation and response to prominent warming, especially after the 1990s, is further investigated because it is concerned whether ice records have absence. A δ^18O series of a Laohugou （LHG） shallow ice core （20.12 m） in the northeastern Tibetan Plateau was reconstructed covering the period of 1960–2006. The ice core δ^18O record had sig-nificant positive correlations with the warm season （May–September） air temperatures at adjacent meteorological stations and the 500 hPa temperatures in boreal China, indicating that the δ^18O record could be considered a credible proxy of regional temperature. A clear, cold temperature event in 1967 and rapid warming after the 1990s were captured in the LHG δ^18O series, revealing that it could record extreme air-temperature events on both regional and global scales. The LHG δ^18O variations had evident positive correlations with both the summer surface outgoing longwave radiation （OLR） in the Mongolia region and the summer meridional wind at 500 hPa in the LHG region during 1960–2006, suggesting that the increased OLR in the Mongolia region might have intensified the Mongolia Low and expanded the pressure gradient to the LHG region （the Shulehe High）, which would have pushed the westerlies further north and suppressed southward incursions of cold air into the LHG region, and thus augmented the temperature rise. The regional atmospheric circulation difference （1985–2006 minus 1960–1984） suggested that the anticyclone in the Mongolia region might have developed the easterly wind, which transported warmer air from the east toward the LHG region and weakened the cold penetration of the westerlies, resulting in the temperature rise since the middle 1980s.

Precipitation Extremes Analysis over the Brazilian Northeast via Logistic Regression

This work diagnosed the precipitation extremes over the Brazilian Northeast (NEB) based on logistic regression for obtaining associations between precipitation extremes and the meteorological variables by Odd Ratio (OR). Data of ten meteorological variables to the NEB (North (NNEB), East (ENEB), South (SNEB) and Semiarid (SANEB)) were used daily. The OR results evidenced that the outgoing longwave radiation was the key variable on the precipitation extremes detection in three sub-regions: ENEB with 2.91 times (95% confidence interval (CI): 2.11, 4.02), NNEB with 3.63 times (95% CI: 1.93, 6.83), and SANEB with 5.40 times (95% CI: 3.04, 9.61);while on SNEB, it was relative humidity with 3.88 times (95% CI: 2.89, 5.20) more chance to favor the precipitation extremes. The maximum temperature, zonal wind component, evaporation, specific humidity and RH also had influence on these extremes. Goodness-of-fit and ROC analysis demonstrated that all models had a good fit and good predictive capability.

CLIMATIC CHARACTERISTICS OF NET RADIATION IN THE EARTH-ATMOSPHERE SYSTEM OVER CHINA

Investigated are effects of the total cloudiness and other factors on earth-atmosphere net radia- tion(EANR)and analyzed is its relation to other components and ground surface net radiation in the context of ERBE and ISCCP.Evidence suggests that planetary scale albedo and earth-atmo- sphere short wave absorption radiation have maximum effect on the net radiation under study,with the influence of cloud and latitude displayed predominantly through the two factors;OLR has rela- tively weak effect;the earth-atmosphere net radiation is well correlated with surface net radiation. Analysis is also performed of the geographic distribution of the earth-atmosphere net radiation throughout China,and the annual curve of the net radiation on a local basis is marked by high (low)value in summer(winter)with the impact of factors.including total cloudiness responsible largely for the shift of the months with maximum.

Evaluation of FY-3B Reprocessed OLR Data in the Asian–Australian Monsoon Region during 2011–2019:Comparison with NOAA OLR

The present study evaluates spatial and temporal characteristics of the Fengyun-3 B(FY-3 B)’s outgoing longwave radiation(OLR)data based on NOAA OLR data and the GPCP(Global Precipitation Climatology Project)precipitation data over the Asian-Australian region during 2011-2019.In terms of climatological distribution patterns and interannual standard deviation,FY-3 BOLR are quite consistent with NOAA OLR,with annual and seasonal pattern correlation coefficients all exceeding 0.93.There are some discrepancies in the OLR magnitude between FY-3 B and NOAA,especially for the OLR climatology;the climatological OLR from FY-3 B are systematically larger than those from NOAA over the whole study region.In addition,examination of the temporal correlation coefficients between OLR and precipitation over the Asian-Australian monsoon(AAM)region reveals that both of the OLR datasets have captured the widespread negative correlation with precipitation,and FY-3 BOLR exhibits a stronger relationship to precipitation over land.Moreover,FY-3 BOLR exhibits better responses to the precipitation anomalies over India during the extreme El Nino and La Nina events.These results suggest that the FY-3 B OLR dataset is of high quality and worthy of further global application.

Evaluation of the Madden–Julian Oscillation in Fengyun-3B Polar-Orbiting Satellite Reprocessed OLR Data

The present study compares the spatial and temporal characteristics of the Madden-Julian Oscillation(MJO)in Fengyun-3B(FY-3B)polar-orbiting satellite reprocessed outgoing longwave radiation(OLR)data and NOAA OLR data during 2011-2020.The spatial distributions of climatological mean and intraseasonal standard deviation of FY-3B OLR during boreal winter(November-April)and boreal summer(May-October)are highly consistent with those of NOAA OLR.The FY-3B and NOAA OLRs display highly consistent features in the wavenumber-frequency spectra,the occurrence frequency of MJO active days,the eastward propagation of MJO along the equator,and the interannual variability of MJO according to diagnoses using the all-season multivariate EOF analysis.These results indicate that the FY-3B OLR produced by the polar-orbiting satellites is of high quality and worthy of global application.