A clustering methodology is applied to cloud optical depth (τ)–cloud top pressure (TAU-PC) histograms from the new 18 resolution ISCCP-H dataset to derive an updated global weather state (WS) ...dataset. Then, TAU-PC histograms from current-climate CMIP6 model simulations are assigned to the ISCCP-H WSs along with their concurrent radiation and precipitation properties to evaluate model cloud, radiation, and precipitation properties in the context of the weather states. The new ISCCP-H analysis produces WSs that are very similar to those previously found in the lower-resolution ISCCP-D dataset. The main difference lies in the splitting of the ISCCP-D thin stratocumulus WS between the ISCCP-H shallow cumulus and stratocumulus WSs, which results in the reduction by one of the total WS number. The evaluation of the CMIP6 models against the ISCCP-H weather states shows that, in the ensemble mean, the models are producing an adequate representation of the frequency and geographical distribution of the WSs, with measurable improvements compared to the WSs derived for the CMIP5 ensemble. However, the frequency of shallow cumulus clouds continues to be underestimated, and, in some WSs the good agreement of the ensemble mean with observations comes from averaging models that significantly overpredict and underpredict the ISCCP-HWS frequency. In addition, significant biases exist in the internal cloud properties of the model WSs, such as the model underestimation of cloud fraction in middle-top clouds and secondarily in midlatitude storm and stratocumulus clouds, that result in an underestimation of cloud SW cooling in those regimes.
This paper describes the new global long-term International Satellite Cloud
Climatology Project (ISCCP) H-series climate data record (CDR). The H-series
data contain a suite of level 2 and 3 products ...for monitoring the
distribution and variation of cloud and surface properties to better
understand the effects of clouds on climate, the radiation budget, and the
global hydrologic cycle. This product is currently available for public use
and is derived from both geostationary and polar-orbiting satellite imaging
radiometers with common visible and infrared (IR) channels. The H-series data
currently span July 1983 to December 2009 with plans for continued
production to extend the record to the present with regular updates. The
H-series data are the longest combined geostationary and polar orbiter
satellite-based CDR of cloud properties. Access to the data is provided in
network common data form (netCDF) and archived by NOAA's National Centers for
Environmental Information (NCEI) under the satellite Climate Data Record
Program (https://doi.org/10.7289/V5QZ281S). The basic
characteristics, history, and evolution of the dataset are presented herein
with particular emphasis on and discussion of product changes between the
H-series and the widely used predecessor D-series product which also spans
from July 1983 through December 2009. Key refinements included in the ISCCP
H-series CDR are based on improved quality control measures, modified
ancillary inputs, higher spatial resolution input and output products,
calibration refinements, and updated documentation and metadata to bring the
H-series product into compliance with existing standards for climate data
records.
Increasing global precipitation has been associated with a warming climate resulting from a strengthening of the hydrological cycle. This increase, however, is not spatially uniform. Observations and ...models have found that changes in rainfall show patterns characterized as 'wet-gets-wetter' and 'warmer-gets-wetter'. These changes in precipitation are largely located in the tropics and hence are probably associated with convection. However, the underlying physical processes for the observed changes are not entirely clear. Here we show from observations that most of the regional increase in tropical precipitation is associated with changes in the frequency of organized deep convection. By assessing the contributions of various convective regimes to precipitation, we find that the spatial patterns of change in the frequency of organized deep convection are strongly correlated with observed change in rainfall, both positive and negative (correlation of 0.69), and can explain most of the patterns of increase in rainfall. In contrast, changes in less organized forms of deep convection or changes in precipitation within organized deep convection contribute less to changes in precipitation. Our results identify organized deep convection as the link between changes in rainfall and in the dynamics of the tropical atmosphere, thus providing a framework for obtaining a better understanding of changes in rainfall. Given the lack of a distinction between the different degrees of organization of convection in climate models, our results highlight an area of priority for future climate model development in order to achieve accurate rainfall projections in a warming climate.
The salient features of the daytime cloud radiative effect (CRE, also known as cloud radiative forcing) corresponding to various cloud regimes or weather states are examined. The analysis is based on ...a 24 year long data set from the International Satellite Cloud Climatology Project (ISCCP) for three distinct geographical zones covering most of the Earth's surface area. Conditional sampling and averaging of the ISCCP cloud fraction and CRE in 2.5° grid cells is performed for each weather state, and the state's radiative importance expressed as the relative contribution to the total CRE of its geographical zone is explained in terms of dominant cloud type, cloud fraction, and frequency of occurrence. Similarities and differences within and between geographical zones in the cloud fraction and CRE characteristics of the various weather states are identified and highlighted. By providing an exposition of the radiative energy characteristics of different cloud type mixtures, we facilitate the meteorological situation‐dependent evaluation of radiation budget effects due to clouds in climate models.
Key Points
The Cloud Radiative Forcing can be partitioned by cloud regime
CRF by cloud regime can be used as a higher order GCM diagnostic
ISCCP cloud regimes are radiatively distinct
There are notable differences in the joint histograms of cloud top height and optical depth being produced from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multiangle Imaging ...Spectro‐Radiometer (MISR) and by the International Satellite Cloud Climatology Project (ISCCP). These differences have their roots in the different retrieval approaches used by the three projects and are driven largely by responses of the retrievals to (1) stratocumulus (or more broadly low‐level clouds under temperature inversions), (2) small (subpixel) or broken low‐level clouds, and (3) multilayer clouds. Because each data set has different strengths and weakness, the combination tells us more about the observed cloud fields than any of the three by itself. In particular, the MISR stereo height retrieval provides a calibration insensitive approach to determining cloud height that is especially valuable in combination with ISCCP or MODIS because the combination provides a means to estimate the amount of multilayer cloud, where the upper cloud is optically thin. In this article we present a review of the three data sets using case studies and comparisons of annually averaged joint histograms on global and regional scales. Recommendations for using these data in climate model evaluations are provided.
We continue reconstructing Earth's radiation budget from global observations in as much detail as possible to allow diagnosis of the effects of cloud (and surface and other atmospheric constituents) ...variations on it. This new study was undertaken to reduce the most noticeable systematic errors in our previous results (flux data set calculated mainly using International Satellite Cloud Climatology Project–C1 input data (ISCCP‐FC)) by exploiting the availability of a more advanced NASA Goddard Institute for Space Studies (GISS) radiative transfer model and improved ISCCP cloud climatology and ancillary data sets. The most important changes are the introduction of a better treatment of ice clouds, revision of the aerosol climatology, accounting for diurnal variations of surface skin/air temperatures and the cloud‐radiative effects on them, revision of the water vapor profiles used, and refinement of the land surface albedos and emissivities. We also extend our previous flux results, limited to the top of atmosphere (TOA) and surface (SRF), to also include three levels within the atmosphere, forming one integrated vertical atmospheric flux profile from SRF to TOA, inclusive, by combining a new climatology of cloud vertical structure with the ISCCP cloud product. Using the new radiative transfer model and new input data sets, we have produced an 18‐year at 3‐hour time steps, global at 280‐km intervals, radiative flux profile data set (called ISCCP‐FD) that provides full‐ and clear‐sky, shortwave and longwave, upwelling and downwelling fluxes at five levels (SRF, 680 mbar, 440 mbar, 100 mbar, and TOA). Evaluation is still only possible for TOA and SRF fluxes: Comparisons of monthly, regional mean values from FD with Earth Radiation Budget Experiment, Clouds and the Earth's Radiant Energy System and Baseline Surface Radiation Network values suggest that we have been able to reduce the overall uncertainties from 10–15 to 5–10 W/m2 at TOA and from 20–25 to 10–15 W/m2 at SRF. Annual mean pressure‐latitude cross sections of the cloud effects on atmospheric net radiative fluxes show that clouds shift the longwave cooling downward in the Intertropical Convergence Zone, acting to stabilize the tropical atmosphere while increasing the horizontal heating gradient forcing the Hadley circulation, and shift the longwave cooling upward in the midlatitude storm zones, acting to destabilize the baroclinic zones while decreasing the horizontal heating gradient there.
The Ganga‐Brahmaputra accounts for ∼25% of the total amount of freshwater received by the Bay of Bengal. Using daily in situ river discharge data along with altimetry‐derived river heights, the ...present study aims to produce a monthly data set of altimetry‐derived Ganga‐Brahmaputra River discharge at the river mouths for 1993–2008. First, we estimate the standard error of ENVISAT‐derived water levels over the Ganga to be 0.26 m, much smaller than the range of variability of ∼7 m, and consistent with the accuracy of altimeter measurements over large rivers. We then establish rating curves between altimetry‐derived water levels and in situ river discharges and show that TOPEX‐Poseidon, ERS‐2, and ENVISAT data can successfully be used to infer Ganga and Brahmaputra discharge. The mean error on the estimated daily discharge derived from altimetry ranges from ∼15% (∼4700 m3/s) using TOPEX‐Poseidon over the Brahmaputra to ∼36% (∼9000 m3/s) using ERS‐2 over the Ganga. Combined Ganga‐Brahmaputra monthly discharges for 1993–2008 are presented, showing a mean error of ∼17% (∼2700 m3/s), within the range (15%–20%) of acceptable accuracy for discharge measurements. During 2004–2008, we assess the variability of the estimate against precipitation and river heights records. Finally, we present a basic approach to infer Ganga‐Brahmaputra monthly discharge at the river mouths. The upscaled discharge exhibits a marked interannual variability with a standard deviation in excess of ∼12,500 m3/s, much larger than the data set uncertainty. This new data set represents an unprecedented source of information to quantify continental freshwater forcing flux into Indian Ocean circulation models.
Synoptically Driven Arctic Winter States Stramler, Kirstie; Del Genio, Anthony D.; Rossow, William B.
Journal of climate,
03/2011, Letnik:
24, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The dense network of the Surface Heat Budget of the Arctic (SHEBA) observations is used to assess relationships between winter surface and atmospheric variables as the SHEBA site came under the ...influence of cyclonic and anticyclonic atmospheric circulation systems. Two distinct and preferred states of subsurface, surface, atmosphere, and clouds occur during the SHEBA winter, extending from the oceanic mixed layer through the troposphere and preceded by same-sign variations in the stratosphere. These states are apparent in distributions of surface temperature, sensible heat and longwave radiation fluxes, ocean heat conduction, cloud-base height and temperature, and in the atmospheric humidity and temperature structure.
Surface and atmosphere are in radiative–turbulent–conductive near-equilibrium during a warm opaquely cloudy-sky state, which persists up to 10 days and usually occurs during the low surface pressure phase of a baroclinic wave, although occasionally occurs during the high surface pressure phase because of low, scattered clouds. Clouds occurring in this state have near-unity emissivity and the lowest bases in the vicinity of, or below, the temperature inversion peak. A cold radiatively clear-sky state persists up to two weeks, and occurs only in the high surface pressure phase of a baroclinic wave. The radiatively clear state has clouds that are too tenuous when surface based or, irrespective of opacity, located too far aloft to contribute significantly to the surface energy budget. There is a 13-K surface temperature difference between the two states, and atmospheric inversion peak temperatures are linearly related to the surface temperature in both states. The snow–sea ice interface temperature oscillates over the course of the winter season, as it cools during the radiatively clear state and is warmed from atmospheric emission above and ocean heat conduction from below during the opaquely cloudy state.
Analysis of satellite data over the Arctic from 70°–90°N indicates that the radiatively clear and opaquely cloudy states observed at SHEBA may be representative of the entire Arctic basin. The results suggest that model formulation inadequacies should be easier to diagnose if modeled energy transfers are compared with observations using process-based metrics that acknowledge the bimodal nature of the Arctic ocean–ice–snow–atmosphere column, rather than monthly and regionally averaged quantities. Climate change projections of thinner Arctic sea ice and larger advective water vapor influxes into the Arctic could yield different frequencies of occupation of the radiatively clear and opaquely cloudy states and higher wintertime temperatures of SHEBA ocean, ice, snow, atmosphere, and clouds—in particular, a wintertime warming of the snow–sea ice interface temperature.
Abstract
ISCCP continues to quantify the global distribution and diurnal-to-interannual variations of cloud properties in a revised version. This paper summarizes assessments of the previous version, ...describes refinements of the analysis and enhanced features of the product design, discusses the few notable changes in the results, and illustrates the long-term variations of global mean cloud properties and differing high cloud changes associated with ENSO. The new product design includes a global, pixel-level product on a 0.1° grid, all other gridded products at 1.0°-equivalent equal area, separate satellite products with ancillary data for regional studies, more detailed, embedded quality information, and all gridded products in netCDF format. All the data products including all input data, expanded documentation, the processing code, and an operations guide are available online. Notable changes are 1) a lowered ice–liquid temperature threshold, 2) a treatment of the radiative effects of aerosols and surface temperature inversions, 3) refined specification of the assumed cloud microphysics, and 4) interpolation of the main daytime cloud information overnight. The changes very slightly increase the global monthly mean cloud amount with a little more high cloud and a little less middle and low cloud. Over the whole period, total cloud amount slowly decreases caused by decreases in cumulus/altocumulus; consequently, average cloud-top temperature and optical thickness have increased. The diurnal and seasonal cloud variations are very similar to earlier versions. Analysis of the whole record shows that high cloud variations, but not low clouds, exhibit different patterns in different ENSO events.
Recent work using observational data from the International Satellite Cloud Climatology Project (ISCCP) and reanalysis products suggests that African easterly waves (AEWs) form in association with a ...“transition” process from smaller and scattered convection into larger and organized mesoscale convective activity. However, the transition process is unclear and how mesoscale convection initiates AEWs is not well understood. Analysis based on 25 years of ISCCP and reanalysis datasets show that increasing intradiurnal activity, atmospheric instability, and specific humidity precede the development of well-organized convection over the Ethiopian highlands. Atmospheric instability favors a high frequency of scattered, isolated convection to the east of the Ethiopian highlands, first, followed by a continuing and large increase in instability and increasing humidity, which supports well-organized larger-scale convection. The timing of the changes of thermodynamic variables shows that the dominant transition process is scattered, with weakly organized convection transitioning into the well-organized mesoscale convection, and this initiates the AEWs. Slightly before the mesoscale convection peaks over the Ethiopian highlands, low-level moist westerlies, low- to midlevel wind shear, and positive relative vorticity increase over the region. Evidence shows that the large-scale and local environment enables the scattered and less well-organized convection to merge and form larger and well-organized convection. The dynamic processes suggest that the dominant pathway for AEW initiation is scattered convection transitioning to large and well-organized convection over the Ethiopian highlands and this initiates AEWs westward of the Ethiopian highlands.
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