World Climate Research Programme Research Articles

Tropical water vapor correction for remotely sensed sea surface temperature: Results using narrowband window radiance profiles from TOGA COARE

This paper describes sea surface skin temperatures (SST) derived from unique aircraft‐based measurements and a physical multispectral retrieval technique. The aircraft data were acquired under moist atmospheric conditions over the western and eastern tropical Pacific Ocean during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment and the Central Equatorial Pacific Experiment. Radiometric profiles were obtained in four contiguous channels over the spectral window region 800–1000 cm−1 during aircraft ascents from 0.03 through 4.6 km altitude. These bands subdivide the “split window” of present satellite radiometers used for measurements of SST. The use of four channels in the measurement approach was motivated by theoretical studies that suggest the need for three independent pieces of information to separate atmospheric and surface components of upwelling radiance in moist atmospheres. The analyses were unusual in that the absorption path length differed for each multispectral set of nadir observations made at discrete altitudes. The mean accuracy for retrievals at all altitudes was ≲1 K and was relatively insensitive to the guess profiles used for the simple forward radiance model. Simulated four‐channel retrievals demonstrate an rms accuracy of ≃0.3 K with negligible bias for global maritime profile conditions, which include extreme moisture‐laden samples. The results demonstrate that the combination of high‐precision measurements with a robust retrieval method can provide SST (instantaneous, global, day, or night) that meet the World Climate Research Programme accuracy objectives.

New network to monitor climate change

Recent reports by the World Climate Research Programme and the National Research Council, including “Adequacy of Climate Observing Systems” (1999), have noted that current observational networks are inadequate for monitoring the Earth's climate system. The accuracy and fidelity of the data used to measure climate variability are crucial to both U.S. government monitoring efforts and U.S. industry. Even small biases can alter the interpretation of decadal climate variability and change. Although the United States is a leader in climate research, no national observing network is capable of ensuring long‐term climate records free of artificial biases—also known as inhomogeneitie—due to factors such as instrument changes, station relocations, and changes in the surrounding environment.

The SAO and Kelvin waves in the EuroGRIPS GCMS and the UK Met. Office analyses

Abstract. We compare the tropical oscillations and planetary scale Kelvin waves in four troposphere-stratosphere climate models and the assimilated dataset produced by the United Kingdom Meteorological Office (UKMO). The comparison has been made in the GRIPS framework "GCM-Reality Intercomparison Project for SPARC", where SPARC is Stratospheric Processes and their Role in Climate, a project of the World Climate Research Program. The four models evaluated are European members of GRIPS: the UKMO Unified Model (UM), the model of the Free University in Berlin (FUB–GCM), the ARPEGE-climat model of the French National Centre for Meteorological Research (CNRM), and the Extended UGAMP GCM (EUGCM) of the Centre for Global Atmospheric Modelling (CGAM). The integrations were performed with different, but annually periodic external conditions (e.g., sea-surface temperature, sea ice, and incoming solar radiation). The structure of the tropical winds and the strengths of the Kelvin waves are examined. In the analyses where the SAO (Semi-Annual Oscillation) and the QBO (Quasi-Biennal Oscillation) are reasonably well captured, the amplitude of these analysed Kelvin waves is close to that observed in independent data from UARS (Upper Atmosphere Research Satellite). In agreement with observations, the Kelvin waves generated in the models propagate into the middle atmosphere as wave packets, consistent with a convective forcing origin. In three of the models, slow Kelvin waves propagate too high and their amplitudes are overestimated in the upper stratosphere and in the mesosphere, the exception is the UM which has weaker waves. None of the modelled waves are sufficient to force realistic eastward phases of the QBO or SAO. Although the SAO is represented by all models, only two of them are able to generate westerlies between 10 hPa and 50 hPa. The importance of the role played in the SAO by unresolved gravity waves is emphasized. Although it exhibits some unrealistic features, the EUGCM, which includes a parametrization of gravity waves with a non-zero phase speed, is able to simulate clear easterly to westerly transitions as well as westerlies with down-ward propagation. Thermal damping is also important for the westerly forcing in the stratosphere.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; tropical meterology; waves and tides)

The role of space in sparc research

Abstract The research project on Stratospheric Processes And their Role in Climate (SPARC), was set up in 1992 by the World Climate Research Programme (WCRP) to help the stratospheric research community focus on the issues of importance for climate. In this paper, we present the atmospheric data requirements of the SPARC research community, in particular the needs for monitoring of climate and for understanding stratospheric processes. We present briefly the work carried out by the SPARC project and illustrate the role of space in this work using recent results from research carried out by SPARC working groups and the stratospheric research community. Advantages of space-based data are presented, as are their weaknesses, the lessons learned when using such data for monitoring purposes and the challenges posed to future generations of space-based instruments.

Climate monitoring from operational satellites: accomplishments, problems, and prospects

This paper reviews some of the long-term data sets, including those of the World Climate Research Program, constructed from the observations of the operational satellites. Operational weather satellites provide the long-term sustained observations needed for monitoring changes in the Earth's climate. But because the satellites have been designed for weather applications, they lack the orbital and instrumental stabilities needed for measuring the smaller signals associated with decadal climate trends. The lack of onboard calibration of the visible and near-infrared imagers, and the drift in local observing time during a satellite's lifetime, introduce uncertainties in the climatic time series. These effects are illustrated and attempts to correct for them are described. Contributions of these data sets to both seasonal to interrannual, and decadal, climate monitoring are illustrated. Planned improvements in future satellites will significantly enhance our capability to monitor climate from space.

A comparison of scavenging and deposition processes in global models: results from the WCRP Cambridge Workshop of 1995

We report on results from a World Climate Research Program workshop on representations of scavenging and deposition processes in global transport models of the atmosphere. 15 models were evaluated by comparing simulations of radon, lead, sulfur dioxide, and sulfate against each other, and against observations of these constituents. This paper provides a survey on the simulation diVerences between models. It identifies circumstances where models are consistent with observations or with each other, and where they diVer from observations or with each other. The comparison shows that most models are able to simulate seasonal species concentrations near the surface over continental sites to within a factor of 2 over many regions of the globe. Models tend to agree more closely over source (continental) regions than for remote (polar and oceanic) regions. Model simulations diVer most strongly in the upper troposphere for species undergoing wet scavenging processes. There are not a suYcient number of observations to characterize the climatology (long-term average) of species undergoing wet scavenging in the upper troposphere. This highlights the need for either a diVerent strategy for model evaluation (e.g., comparisons on an event by event basis) or many more observations of a few carefully chosen constituents.

Ocean data synthesis offers research opportunities

The World Ocean Circulation Experiment (WOCE),an international research effort aimed at understanding the role of ocean circulation in climate, recently completed its first observational phase. The second phase, which began in late 1997, is dedicated to analysis, interpretation, modeling, and synthesis (AIMS) of the different data sets into a coherent whole. A description of the objectives of AIMS is given in WOCE IPO Report 153 [WOCE, 1997] .While WOCE's position as a component of the World Climate Research Programme will end formally in 2002, the AIMS phase will certainly continue beyond that date.

Electronic atlas of WOCE hydrographic and tracer data now available

During the last decade, as part of the World Climate Research Programme, the World Ocean Circulation Experiment (WOCE) produced a global set of hydrographic, nutrient, and tracer data of unprecedented quality and quantity Large parts of this data set are now publicly available and are being used for general oceanographic research and climate studies. However, widespread use of the combined WOCE data set is hampered; the data reside in many separate data files and the file format is complex.To facilitate the use of the global WOCE data set, all data released by the WOCE Hydrographic Programme (WHP) have been compiled into an integrated data set. When used with the Ocean Data View visualization software for Windows, this data set constitutes an “Electronic Atlas of WOCE Data” (eWOCE) that permits graphical display and interactive analysis of the data in many different ways. With extensive interactive controls such as user‐defined plot configuration, zooming, auto‐scaling, color adjustment, and station/sample selection, this electronic atlas complements and surpasses printed atlases that are now in preparation.

The GCM–Reality Intercomparison Project for SPARC (GRIPS): Scientific Issues and Initial Results

To investigate the effects of the middle atmosphere on climate, the World Climate Research Programme is supporting the project “Stratospheric Processes and their Role in Climate” (SPARC). A central theme of SPARC, to examine model simulations of the coupled troposphere–middle atmosphere system, is being performed through the initiative called GRIPS (GCM-Reality Intercomparison Project for SPARC). In this paper, an overview of the objectives of GRIPS is given. Initial activities include an assessment of the performance of middle atmosphere climate models, and preliminary results from this evaluation are presented here. It is shown that although all 13 models evaluated represent most major features of the mean atmospheric state, there are deficiencies in the magnitude and location of the features, which cannot easily be traced to the formulation (resolution or the parameterizations included) of the models. Most models show a cold bias in all locations, apart from the tropical tropopause region where they can be either too warm or too cold. The strengths and locations of the major jets are often misrepresented in the models. Looking at three-dimensional fields reveals, for some models, more severe deficiencies in the magnitude and positioning of the dominant structures (such as the Aleutian high in the stratosphere), although undersampling might explain some of these differences from observations. All the models have shortcomings in their simulations of the present-day climate, which might limit the accuracy of predictions of the climate response to ozone change and other anomalous forcing.

A comparison of scavenging and deposition processes in global models: results from the WCRP Cambridge Workshop of 1995

We report on results from a World Climate Research Program workshop on representations ofscavenging and deposition processes in global transport models of the atmosphere. 15 modelswere evaluated by comparing simulations of radon, lead, sulfur dioxide, and sulfate against eachother, and against observations of these constituents. This paper provides a survey on the simulationdifferences between models. It identifies circumstances where models are consistent withobservations or with each other, and where they differ from observations or with each other. Thecomparison shows that most models are able to simulate seasonal species concentrations nearthe surface over continental sites to within a factor of 2 over many regions of the globe. Modelstend to agree more closely over source (continental) regions than for remote (polar and oceanic)regions. Model simulations differ most strongly in the upper troposphere for species undergoingwet scavenging processes. There are not a sufficient number of observations to characterize theclimatology (long-term average) of species undergoing wet scavenging in the upper troposphere.This highlights the need for either a different strategy for model evaluation (e.g., comparisons onan event by event basis) or many more observations of a few carefully chosen constituents.

Advances in Understanding Clouds from ISCCP

This progress report on the International Satellite Cloud Climatology Project (ISCCP) describes changes made to produce new cloud data products (D data), examines the evidence that these changes are improvements over the previous version (C data), summarizes some results, and discusses plans for the ISCCP through 2005. By late 1999 all datasets will be available for the period from July 1983 through December 1997. The most significant changes in the new D-series cloud datasets are 1) revised radiance calibrations to remove spurious changes in the long-term record, 2) increased cirrus detection sensitivity over land, 3) increased low-level cloud detection sensitivity in polar regions, 4) reduced biases in cirrus cloud properties using an ice crystal microphysics model in place of a liquid droplet microphysics model, and 5) increased detail about the variations of cloud properties. The ISCCP calibrations are now the most complete and self-consistent set of calibrations available for all the weather satellite imaging radiometers: total relative uncertainties in the radiance calibrations are estimated to be ≲ 5% for visible and ≲ 2% for infrared; absolute uncertainties are < 10% and < 3%, respectively. Biases in (detectable) cloud amounts have been reduced to ≲ 0.05, except in the summertime polar regions where the bias may still be ~ 0.10. Biases in cloud-top temperatures have been reduced to ≲ 2 K for lower-level clouds and ≲ 4 K for optically thin, upper-level clouds, except when they occur over lower-level clouds. Using liquid and ice microphysics models reduces the biases in cloud optical thicknesses to ≲ 10%, except in cases of mistaken phase identification; most of the remaining bias is caused by differences between actual and assumed cloud particle sizes and the small effects of cloud variations at scales < 5 km. Global mean cloud properties averaged over the period July 1983–June 1994 are the following: cloud amount = 0.675 ± 0.012; cloud-top temperature = 261.5 ± 2.8 K; and cloud optical thickness = 3.7 ± 0.3, where the plus–minus values are the rms deviations of global monthly mean values from their long-term average. Long-term, seasonal, synoptic, and diurnal cloud variations are illustrated. The ISCCP dataset quantifies the variations of cloud properties at mesoscale resolution (3 h, 30 km) covering the whole globe for more than a decade, making it possible to study cloud system evolution over whole life cycles, watching interactions with the atmospheric general circulation. Plans for the next decade of the World Climate Research Programme require continuing global observations of clouds and the most practical way to fulfill this requirement is to continue ISCCP until it can be replaced by a more capable system with similar time resolutions and global coverage.

A midterm report on the GEWEX Continental‐Scale International Project (GCIP)

The GEWEX Continental‐Scale International Project (GCIP) is being carried out in the Mississippi River Basin under the auspices of the World Climate Research Program and its Global Energy and Water Cycle Experiment (GEWEX). This paper provides a brief history of GCIP's development and its mission and objectives. The scientific achievements of GCIP are then reviewed against each of these objectives. The paper concludes with a brief discussion of options for the period beyond 2000 after the current phase of the project is completed.

Global Climate Project shows early promise

The implementation of a global climate project and its early results are being hailed as exciting leaps forward in climate research that have enormous potential for improving predictions of interannual variations, as well as improving the understanding and modeling, and possibly developing predictive capabilities, of decadal and longer variability and climate change. Known as the Climate Variability and Predictability (CLIVAR) project of the World Climate Research Programme (WCRP),its most recent achievements have included observations, predictions, and documentation of the evolution of the 1997–1998 El Niño and that event's progression into the 1998 La Niña. In place to accomplish this was CLIVAR's full tropical Pacific observing system and new coupled atmosphere‐upper ocean models.Even more exciting was that prediction models were able to capture aspects of the differences in teleconnection patterns between this El Niño and previous events, pointing to the importance of sea surface temperature patterns globally Exciting new possibilities also have emerged through profiling floats deployed at various depths that come to the surface every week or two to give ocean soundings of temperature and salinity, while their displacements provide estimates of ocean currents at depth.

Optimal Measurement of Surface Shortwave Irradiance Using Current Instrumentation

Abstract Although most measurements of total downwelling shortwave irradiance are made with pyranometers, the World Climate Research Program’s Baseline Surface Radiation Network has recommended the use of the summation of shortwave components in which the direct normal irradiance is measured and multiplied by the cosine of the solar zenith angle and then added to the diffuse horizontal irradiance measured by a pyranometer that is shaded from direct solar radiation by a disk. The nonideal angular response of most pyranometers limits their accuracy to about 3%, or 20–30 W m−2, for instantaneous clear-sky measurements. An intensive study of 21 separate measurements of total horizontal irradiance was conducted during extreme winter conditions of low sun and cold temperatures over 12 days at the National Oceanic and Atmospheric Administration’s Climate Monitoring and Diagnostics Laboratory. The experiment showed that the component sum methodology could lower the uncertainty by a factor of 2 or 3. A clear demon...

An Overview of the Results of the Atmospheric Model Intercomparison Project (AMIP I)

Abstract The Atmospheric Model Intercomparison Project (AMIP), initiated in 1989 under the auspices of the World Climate Research Programme, undertook the systematic validation, diagnosis, and intercomparison of the performance of atmospheric general circulation models. For this purpose all models were required to simulate the evolution of the climate during the decade 1979—88, subject to the observed monthly average temperature and sea ice and a common prescribed atmospheric CO2 concentration and solar constant. By 1995, 31 modeling groups, representing virtually the entire international atmospheric modeling community, had contributed the required standard output of the monthly means of selected statistics. These data have been analyzed by the participating modeling groups, by the Program for Climate Model Diagnosis and Intercomparison, and by the more than two dozen AMIP diagnostic subprojects that have been established to examine specific aspects of the models' performance. Here the analysis and valida...

Baseline Surface Radiation Network (BSRN/WCRP): New Precision Radiometry for Climate Research

To support climate research, the World Climate Research Programme (WCRP) initiated a new radiometric network, the Baseline Surface Radiation Network (BSRN). The network aims at providing validation material for satellite radiometry and climate models. It further aims at detecting long-term variations in irradiances at the earth's surface, which are believed to play an important role in climate change. The network and its instrumentation are designed 1) to cover major climate zones, 2) to provide the accuracy required to meet the objectives, and 3) to ensure homogenized standards for a long period in the future. The limits of the accuracy are defined to reach these goals. The suitable instruments and instrumentations have been determined and the methods for observations and data management have been agreed on at all stations. Measurements of irradiances are at 1 Hz, and the 1-min statistics (mean, standard deviation, and extreme values) with quality flags are stored at a centralized data archive at the WCRP's World Radiation Monitoring Center (WRMC) in Zurich, Switzerland. The data are quality controlled both at stations and at the WRMC. The original 1-min irradiance statistics will be stored at the WRMC for 10 years, while hourly mean values will be transferred to the World Radiation Data Center in St. Petersburg, Russia. The BSRN, consisting of 15 stations, covers the earth's surface from 80°N to 90°S, and will soon be joined by seven more stations. The data are available to scientific communities in various ways depending on the communication environment of the users. The present article discusses the scientific base, organizational and technical aspects of the network, and data retrieval methods; shows various application possibilities; and presents the future tasks to be accomplished.

Uncertainty of monthly rainfall estimates from rain gauges in the Global Precipitation Climatology Project

The Global Precipitation Climatology Project (GPCP), initiated by the World Climate Research Program, has as a main objective the production of monthly global rainfall estimates on a 2.5° × 2.5° longitude/latitude grid by combining different sources of information such as satellite remote sensing and rain gauges. It is important to understand the accuracy of the rain gauge estimates of mean area rainfall because these are considered the most reliable estimates for regions with high numbers of gauges. Methods to model the error resulting from using rain gauge data to estimate the spatially averaged rainfall accumulation have been developed previously. Three of these methods are investigated in this study: an empirical equation derived from rain gauge data, an analytical equation derived from statistical concepts, and an empirical equation derived from theory with parameters determined from calibration. Simulations are performed to determine the utility of these three approaches in estimating the error of the rain gauge mean in the context of the GPCP.

The radiative impact of a simple aerosol climatology on the Hadley Centre atmospheric GCM

AbstractResults from a new version of the Hadley Centre atmospheric general‐circulation model are presented in which the sensitivity of the model to the inclusion of a simple aerosol climatology is investigated. Without aerosols, comparisons with clear‐sky reflected short‐wave radiation from the Earth Radiation Budget Experiment (ERBE) and the Scanner for Radiation Budget (ScaRaB) satellite measurements indicate a missing scatterer in the clear‐sky atmosphere. In addition, recent estimates of global, annual mean absorbed short‐wave radiation at the surface, which used the Global Energy Balance Archive (GEBA) where possible for verification, indicate that the atmosphere did not absorb enough short‐wave radiation. The insertion of a simple aerosol climatology based on World Climate Research Programme recommendations into the model was found to be the only plausible means of reducing its significant short‐wave bias compared with ERBE and ScaRaB measurements at the top of the atmosphere, and with GEBA data at the surface. An increase in the global, annual mean atmospheric absorbed short‐wave radiation accompanied these changes.

Intercomparison and evaluation of atmospheric transport in a Lagrangian model (STOCHEM), and an Eulerian model (UM), using 222Rn as a short‐lived tracer

AbstractTransport of the short‐lived (half‐life 3.83 days) isotope 222Rn, which is emitted from unfrozen soils, is used to compare transport in several versions of the UK Meteorological Office Lagrangian chemistry‐transport model and in the Unified Model, the UK Meteorological Office general circulation model. The same 222Rn experiment is repeated for all the model versions, illustrating the impact on global transport of various model improvements: adding boundary‐layer schemes, including sub‐grid scale convection, increasing model spatial resolution, and increasing the temporal resolution of the meteorological fields used for driving the off‐line model. Results from all model versions are compared with a limited observational data set, and also with results from the same 222Rn simulations carried out with several global atmospheric transport models as part of the World Climate Research Program in December 1993 (Jacob et al. 1997). Versions of the Lagrangian chemistry‐transport model that include sub‐grid scale convection, transport 222Rn in a manner that is similar to the Unified Model and most general circulation models, supporting the simple and computationally inexpensive Lagrangian approach taken.

Report endorses climate study, recommends several research foci

A major study to understand climate variability and predict climate change should proceed in the same direction, a National Research Council (NRC) panel has recommended. The panel also urged the implementation of a number of future research activities. The study, known as the Continental‐Scale Intercomparison Project (GCIP), the first of five continental‐scale projects of the Global Energy and Water Cycle Experiment (GEWEX), began in 1990.Recent efforts to study climate have emphasized the importance of improved understanding of many aspects of the hydrologic cycle and the exchange of energy and water at the atmosphere‐surface interface. To address these issues within the context of the Mississippi River basin, the World Climate Research Programme established the GEWEX GCIP. The NRC established a panel specifically to evaluate and provide scientific leadership and guidance on the scientific strategies, plans, and priorities of the GEWEX Program. This panel's report, “GCIP: A Review of Progress and Opportunities,” also highlighted the major accomplishments of the study so far. It was released June 8 at the GCIP Mississippi River Hydrometeorology Conference in St. Louis, Mo.