Global Distribution Of Total Cloud Cover And Its Linkage To Sea Surface Temperature

Clouds,as the main regulator of earth energy balance,atmospheric circulation and water vapor cycle,are less well understood for their complex and variable distributions,which make clouds and their feedbacks become the largest obstacles for climate prediction.Here we use several different satellite records to extract the spatial-time modes of total cloud cover(TCC)and cloud vertical structure by employing a pairwise rotation of Empirical Orthogonal Function(EOF)analysis to explore the relationship between cloud and Sea surface temperature(SST),providing the reliable observational evidence for the climate model.The main results are as follows:The first three principal modes of TCC are closely associated with the Central Pacific El Ni?o Southern Oscillation(CP ENSO),Eastern Pacific(EP)ENSO and Indian Ocean Dipole(IOD)during the 1980s-2010 s,respectively.While the second and third mode of TCC derived from Moderate Resolution Imaging Spectroradiometer(MODIS)are significantly related to IOD and EP ENSO during the2000s-2010 s,respectively,indicating a less contribution of EP ENSO-like mode of TCC after 2000.The trend modes of TCC are also constructed to investigate long-term cloud responses to SST warming by transferring the linear trends of oscillation modes to the specific modes.The principal components(PCs)of TCC trend modes are strongly correlated with global-mean SST(GSST)with correlation coefficient of about 0.60 during 1980s-2000 s and 0.45 during 2000s-2010 s,suggesting a continued influence of global SST warming on TCC.The spatial pattern of TCC trend during 1980s-2000 s is closely associated with Atlantic Multi-decadal Oscillation(AMO)and Pacific Decadal Oscillation(PDO).In contrast,Pacific Ocean,instead of North Atlantic,seems to have more contribution on TCC trend pattern during 2000s-2010 s.What ismore,Hadley cell(HC)undergoes a significant expansion during 1980s-2000 s owing to the ENSO/PDO cycle transitions to the opposite phase,while the expansion of HC in the Southern Hemisphere is likely to slow down during 2000s-2010 s owing to the ENSO/PDO cycle transitions from cold phase to warm phase.SST could significantly affect the dynamic and thermodynamic conditions of the atmospheric circulation and consequently the cloud variations.For CP ENSO-like mode,there is the significantly ascending motions over the Central Pacific where is associated with the increase of TCC.The anomalous descending motions in the tropics,which is associated with the equatorial symmetric mode of HC,is accompanied by the decreased TCC.For EP ENSO-like mode of TCC,there is the anomalous ascent over the Eastern Pacific and anomalous descent over a large part of the Western Pacific warm pool,which appears to weaken the Walker Circulation.Unlike the seesaw structure in CP El Nino,the anomalous ascent is more concentrated in the SH,which are closely associated with the equatorial asymmetric mode of HC.The different response of clouds to CP and EP El Ni?o highlights the nonlinearity of El Ni?o SST forcing.CP ENSO-like mode is also the first principal mode of zonal and tropical meridional(10oS-10oN)cloud occurrence frequency decomposed from CloudSat observations,which shows an increase of cloud occurrence frequency near the equator and around 40oN/S,and a decrease around 10o-30oN/S in both hemispheres,suggesting a symmetric tightening of HC in CP El Nino years.What is more,the significant increase of high cloud occurrence frequency around the 180o,which is accompanied by an eastward shift of Walker circulation in CP El Ni?o years.In addition,the PCs of the trend modes of the zonal and tropical meridional cloud occurrence frequencies are significantly correlated with the GSST with correlation coefficients of 0.43 and 0.42,respectively.They are also correlated with the PDO with the correlation coefficients of 0.29 and 0.45,respectively,indicating that the change of PDO could significantly impact the trend pattern of cloud occurrence frequency during 2006-2017.