Search Results

You are looking at 1 - 10 of 25 items for

  • Author or Editor: J. A. Curry x
  • All content x
Clear All Modify Search
J. A. Curry and P. J. Webster

How to understand and reason about uncertainty in climate science is a topic that is receiving increasing attention in both the scientific and philosophical literature. This paper provides a perspective on exploring ways to understand, assess, and reason about uncertainty in climate science, including application to the Intergovernmental Panel on Climate Change (IPCC) assessment reports. Uncertainty associated with climate science and the science–policy interface presents unique challenges owing to the complexity of the climate system itself, the potential for adverse socioeconomic impacts of climate change, and the politicization of proposed policies to reduce societal vulnerability to climate change. The challenges to handling uncertainty at the science– policy interface are framed using the “monster” metaphor, whereby attempts to tame the monster are described. An uncertainty lexicon is provided that describes the natures and levels of uncertainty and ways of representing and reasoning about uncertainty. Uncertainty of climate models is interpreted in the context of model inadequacy, uncertainty in model parameter values, and initial condition uncertainty. This article examines the challenges of building confidence in climate models and, in particular, the issue of confidence in simulations of the twenty-first-century climate. The treatment of uncertainty in the IPCC assessment reports is examined, including the IPCC Fourth Assessment Report conclusion regarding the attribution of climate change in the latter half of the twentieth century. Ideas for monster-taming strategies are discussed for institutions, individual scientists, and communities.

Full access
J. A. Curry and G. F. Herman

Abstract

The occurrence of cloudiness over the Beaufort Sea region of the Arctic Basin during June 1980, is related to the ambient large-scale meteorological conditions. Cloud data are obtained from a hand analysis of the visible and infrared Defense Meteorological Satellite Program (DMSP) images and from the U.S. Air Force Three-Dimensional Nephanalysis (3DNEPH). A comparison of the two cloud cover datasets showed good agreement for mid- and high-level cloudiness, but low-level cloudiness was significantly underestimated by the 3DNEPH. The study therefore uses a composite data set consisting of the 3DNEPH data at mid- and upper-levels, and the DMSP data at lower levels. Atmospheric data are obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) objective analysis, and large-scale heat and moisture budgets are constructed. The budgets are used to investigate the processes which contribute to relative humidity changes.

The budgets are related to the cloud cover for both the monthly cloudiness values averaged over the entire region, and for the twice-daily grid point values. Large amounts of low cloud cover during June are attributed primarily to the low level advection of moisture and a residual cooling due to radiation and boundary layer turbulence. The occurrence of midlevel cloudiness is associated with the large-scale transport of heat and moisture. Several relative humidity-based parameterizations currently used in GCMs were tested for their ability to diagnose June 1980 conditions in the Arctic using the initialized fields, but their performance was generally poor. The addition of other atmospheric parameters and budget terms in the empirical formulae provided some improvement, although the agreement with observations remained limited. While our results are dependent upon the quality of the atmospheric and cloud data in this region, they provide further examples of the deficiencies of simple diagnostic layered-cloud parameterizations.

Full access
J. A. Curry and G. F. Herman

Abstract

Aircraft measurements of infrared radiation and cloud microphysics that were collected during the June 1980 Arctic Stratus Experiment are presented and analyzed with the aid of an infrared radiative transfer model. The radiation measurements were obtained with the NCAR Electra's Eppley pyrgeometers and a Barnes PRT-6 radiometer, and the cloud particle observations were obtained with the Knollenberg FSSP and 200X probes.

The data were used to derive values of cloud emittances, mass and volume absorption coefficients, cloud reflectances, cooling rates and radiative extinction lengths. These parameters were found to be strongly dependent on the cloud drop size distribution, and a parameterization of the absorption coefficient in terms of liquid water content and droplet equivalent radius is presented. The window reflectance of the clouds was determined to be between 6.4 and 8.8%.

Full access
G. F. Herman and J. A. Curry

Abstract

A series of clouds-radiation experiments was carried out in June 1980 in Arctic stratus clouds occurring over the Beaufort Sea using the NCAR Electra aircraft. This paper is an analysis of the hemispheric radiation fields obtained with Eppley pyranometers and silicon flux detectors, and the cloud microphysical data obtained with the Knollenberg FSSP and 200X probes. These data were collected in a series of 12 vertical profiles in a variety of boundary layer stratus and altostratus situations. The results are interpreted with the aid of a theoretical radiative transfer model developed by Slingo and Schrecker.

The Knollenberg measurements indicated a wide range of cloud liquid water contents which generally increased from cloud base to cloud top. Values of the equivalent radius of the droplet size distribution are presented. Based on the agreement between the radiation measurements and the model calculations, it is concluded that the Knollenberg FSSP probe produced realistic liquid water concentrations in the present study.

Cloud reflectivity, transmissivity, and absorptivity were obtained with the Eppley pyranometers over the total solar spectrum, and also in the visible and near infrared regions, while the silicon detector produced values over the total spectrum, and in the near-infrared. The reflectivity and transmissivity obtained with the two systems agreed well with each other, and also with the model calculations. The measured values of absorptivity were systematically greater than those predicted, particularly in the visible region.

The theoretical model was used to investigate in each cloud profile the roles of aerosols, gaseous and droplet absorptions, and surface reflectivity. In particular, it was found that Arctic summer aerosol did not significantly affect the bulk radiative properties of the clouds, but did have a large effect on the ratio of diffuse to total radiation above the cloud.

Full access
T. E. Arbetter, J. A. Curry, and J. A. Maslanik

Abstract

Realistic treatment of sea ice processes in general circulation models is needed to simulate properly global climate and climate change scenarios. As new sea ice treatments become available, it is necessary to evaluate them in terms of their accuracy and computational time. Here, several dynamic ice models are compared using both a 2-category and 28-category ice thickness distribution. Simulations are conducted under normal wind forcing, as well as under increased and decreased wind speeds. It is found that the lack of a shear strength parameterization in the cavitating fluid rheology produces significantly different results in both ice thickness and ice velocity than those produced by an elliptical rheology. Furthermore, use of a 28-category ice thickness distribution amplifies differences in the responses of the various models. While the choice of dynamic model is governed by requirements of accuracy and implementation, it appears that, in terms of both parameterization of physical properties and computational time, the elliptical rheology is well-suited for inclusion in a GCM.

Full access
J. A. Curry, J. Maslanik, G. Holland, and J. Pinto
Full access
J. A. Curry, P. J. Webster, and G. J. Holland

The 2005 Atlantic hurricane season was the most active and costly season on record. Recent publications linking an increase in hurricane intensity to increasing tropical sea surface temperatures have fueled the debate on whether or not global warming is causing an increase in hurricane intensity. Because of the substantial implications of the hurricane–global warming issue for society and the immediate policy relevance associated with decision making related to Hurricane Katrina, attacks and rebuttals related to this research are being made in the media and on the World Wide Web without the rigor or accountability expected of scientific discourse. In this paper, we aim to promote a balanced and thoughtful examination of this subject by

  • clarifying the debate surrounding the subject as to whether or not global warming is causing an increase in global hurricane intensity,
  • illustrating a methodology of hypothesis testing to address multiple criticisms of a complex hypothesis that involves a causal chain, and
  • providing a case study of the impact of politics, the media, and the World Wide Web on the scientific process.

Full access
Peter J. Webster, Carol Anne Clayson, and Judith A. Curry

Abstract

The relationship among clouds, surface radiation flux, and the sea surface temperature (SST) of the tropical western Pacific Ocean over the diurnal cycle is addressed in the context of the Atmospheric Radiation Measurement (ARM) Program scientific objectives for the tropical western Pacific Ocean. An understanding of the relationship between clouds and SST on a variety of time and space scales is needed to understand fully the cloud-radiation feedback in the tropical oceans and the maintenance of the warm pool. Here the diurnal cycle is emphasized. Data from the TOGA COARE Intensive Observation Period is examined and interpreted using an ocean mixed layer model that includes a parameterization of the “skin” temperature, explicit salinity, a surface beat budget that includes the sensible heat flux associated with rain, and the contribution of rain to the surface momentum flux. Using a mix of modeling and observations, three different case studies are examined in detail: clear and calm, clear and windy, and disturbed. For these typical sets of conditions and processes in the tropical ocean warm pool, the upper-ocean structure is clarified so that the skin sea surface temperature, the bulk surface temperature (at a depth of 1 cm), and the temperature at 0.5 and 5 m below the surface (which is the level that buoys and ships routinely observe “surface” temperature) can be interpreted. Sensitivity studies are conducted with the model to investigate the roles of wind speed, precipitation, ocean turbidity, and ocean initial state in modulating the radiation-induced diurnal cycle in SST. It is found that in high insolation, low wind regimes that the skin temperature may be as much as 30°C warmer than the 0.5-m buoy temperature. Spatial distribution of the diurnal amplitude of the SST are calculated for the global Tropics, and speculations are made regarding the implication of the SST variability to the tropical climate.

Full access
Hye-Mi Kim, Peter J. Webster, and Judith A. Curry

Abstract

Tropical Pacific Ocean warming has been separated into two modes based on the spatial distribution of the maximum sea surface temperature (SST) anomaly: an east Pacific warming (EPW) and a central Pacific warming (CPW). When combined with east Pacific cooling (EPC), these three regimes are shown to have different impacts on tropical cyclone (TC) activity over the North Pacific by differential modulation of both local thermodynamic factors and large-scale circulation patterns. In EPW years, the genesis and the track density of TCs tend to be enhanced over the southeastern part and suppressed in the northwestern part of the western Pacific by strong westerly wind shear. The extension of the monsoon trough and the weak wind shear over the central Pacific increases the likelihood of TC activity to the east of the climatological mean TC genesis location. In CPW years, the TC activity is shifted to the west and is extended through the northwestern part of the western Pacific. The westward shifting of CPW-induced heating moves the anomalous westerly wind and monsoon trough through the northwestern part of the western Pacific and provides a more favorable condition for TC landfall. The CPW, on the other hand, produces a large suppression of TC activity in the eastern Pacific basin. In EPC years, all of the variables investigated show almost a mirror image of the EPW.

Full access
H. Morrison, J. A. Curry, M. D. Shupe, and P. Zuidema

Abstract

The new double-moment microphysics scheme described in Part I of this paper is implemented into a single-column model to simulate clouds and radiation observed during the period 1 April–15 May 1998 of the Surface Heat Budget of the Arctic (SHEBA) and First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment–Arctic Clouds Experiment (FIRE–ACE) field projects. Mean predicted cloud boundaries and total cloud fraction compare reasonably well with observations. Cloud phase partitioning, which is crucial in determining the surface radiative fluxes, is fairly similar to ground-based retrievals. However, the fraction of time that liquid is present in the column is somewhat underpredicted, leading to small biases in the downwelling shortwave and longwave radiative fluxes at the surface. Results using the new scheme are compared to parallel simulations using other microphysics parameterizations of varying complexity. The predicted liquid water path and cloud phase is significantly improved using the new scheme relative to a single-moment parameterization predicting only the mixing ratio of the water species. Results indicate that a realistic treatment of cloud ice number concentration (prognosing rather than diagnosing) is needed to simulate arctic clouds. Sensitivity tests are also performed by varying the aerosol size, solubility, and number concentration to explore potential cloud–aerosol–radiation interactions in arctic stratus.

Full access