GFDL General Circulation Model Research Articles

Simulating precipitation in the Northeast United States using a climate‐informed K‐nearest neighbour algorithm

AbstractDecadal prediction using climate models faces long‐standing challenges. While global climate models may reproduce long‐term shifts in climate due to external forcing, in the near term, they often fail to accurately simulate interannual climate variability, as well as seasonal variability, wet and dry spells, and persistence, which are essential for water resources management. We developed a new climate‐informed K‐nearest neighbour (K‐NN)‐based stochastic modelling approach to capture the long‐term trend and variability while replicating intra‐annual statistics. The climate‐informed K‐NN stochastic model utilizes historical data along with climate state information to provide improved simulations of weather for near‐term regional projections. Daily precipitation and temperature simulations are based on analogue weather days that belong to years similar to the current year's climate state. The climate‐informed K‐NN stochastic model is tested using 53 weather stations in the Northeast United States with an evident monotonic trend in annual precipitation. The model is also compared to the original K‐NN weather generator and ISIMIP‐2b GFDL general circulation model bias‐corrected output in a cross‐validation mode. Results indicate that the climate‐informed K‐NN model provides improved simulations for dry and wet regimes, and better uncertainty bounds for annual average precipitation. The model also replicates the within‐year rainfall statistics. For the 1961–1970 dry regime, the model captures annual average precipitation and the intra‐annual coefficient of variation. For the 2005–2014 wet regime, the model replicates the monotonic trend and daily persistence in precipitation. These improved modelled precipitation time series can be used for accurately simulating near‐term streamflow, which in turn can be used for short‐term water resources planning and management.

Observed and simulated seasonal co‐variations of outgoing longwave radiation spectrum and surface temperature

We analyze the seasonal variations of Outgoing Longwave Radiation (OLR) accompanying the variations in sea surface temperature (SST) from satellite observations and model simulations, focusing on the tropical oceans where the two quantities are strikingly anti‐correlated. A spectral perspective of this “super‐greenhouse effect” is provided, which demonstrates the roles of water vapor line and continuum absorptions at different altitudes and the influences due to clouds. A model‐satellite comparison indicates that the GFDL General Circulation Model can fairly well represent the total‐sky radiative response to SST in the water vapor infrared absorption band despite the significant bias in the mean state, but this comprises compensating water vapor‐ and cloud‐related errors. The analysis also reveals that the GCM significantly underestimates the cloud induced radiative responses in the window region which arises from the model bias in the mean cloud forcing in convectively active regions. Thus, spectral decomposition proves essential to understand and assess the OLR‐SST relationship and the impacts of water vapor and cloud upon this linkage.

CLIMATE CHHANGE SENSITIVITY ASSESSMENT ON UPPER MISSISSIPPI RIVER BASIN STREAMFLOWS USING SWAT

ABSTRACT: The Soil and Water Assessment Tool (SWAT) model was used to assess the effects of potential future climate change on the hydrology of the Upper Mississippi River Basin (UMRB). Calibration and validation of SWAT were performed using monthly stream flows for 1968–1987 and 1988–1997, respectively. The R2 and Nash-Sutcliffe simulation efficiency values computed for the monthly comparisons were 0.74 and 0.69 for the calibration period and 0.82 and 0.81 for the validation period. The effects of nine 30-year (1968 to 1997) sensitivity runs and six climate change scenarios were then analyzed, relative to a scenario baseline. A doubling of atmospheric CO2 to 660 ppmv (while holding other climate variables constant) resulted in a 36 percent increase in average annual streamflow while average annual flow changes of −49, −26, 28, and 58 percent were predicted for precipitation change scenarios of −20, −10, 10, and 20 percent, respectively. Mean annual streamflow changes of 51,10, 2, −6, 38, and 27 percent were predicted by SWAT in response to climate change projections generated from the CISRO-RegCM2, CCC, CCSR, CISRO-Mk2, GFDL, and HadCMS general circulation model scenarios. High seasonal variability was also predicted within individual climate change scenarios and large variability was indicated between scenarios within specific months. Overall, the climate change scenarios reveal a large degree of uncertainty in current climate change forecasts for the region. The results also indicate that the simulated UMRB hydrology is very sensitive to current forecasted future climate changes.

Simulation of meridional overturning in the upper layer of the South China Sea with an idealized bottom topography

The large-scale upper circulations and meridional overturning in the upper layer of the South China Sea (SCS) with idealized bottom topography in winter and summer are investigated. Simulations with the GFDL general circulation model are carried out under the conditions of open or enclosed boundary regarding transport in the Luzon Strait. The intrusion area of Kuroshio, its impact on the meridional overturning in the upper layer of the SCS and seasonal characteristic of this impact are explored, respectively. The model is forced by climatological wind stress and relaxed to monthly mean climatological temperature and salinity. The resultant meridional overturning is non-enclosed, with transporting from north to south in the surface and returning to north at the depth of about 500 m in winter, about 200 m in summer, with amplitudes of 10(5) m(3)/s. It shows the transporting path of intermediate water of the SCS and offers an idealized reference for further study on dynamics of wind-driven and thermohaline circulation of the SCS.

A climate change database for biological assessments in the Southeastern United States : Development and case study

A regional database containing historical time series and climate change scenarios for the Southeastern United States was developed for the U.S.D.A. Forest Service Southern Global Change Program (SGCP). Daily historical values of maximum temperature, minimum temperature and precipitation and empirically derived estimates of vapor pressure deficit and solar radiation across a uniform 1° latitude × 1° longitude grid were obtained. Climate change scenarios of temperature, precipitation, vapor pressure deficit and solar radiation were generated using semi-empirical techniques which combined historical time series and simulation field summaries from GISS, GFDL, OSU and UKMO General Circulation Model (GCM) experiments. An internally consistent 1° latitude × 1° longitude climate change scenario database was produced in which vapor pressure deficit and solar radiation conditions were driven by the GCM temperature projections, but were not constrained to agree with GCM calculated radiation and humidity fields. Some of the unique characteristics of the database were illustrated through a case study featuring growing season and annual potential evapotranspiration (ETp) estimates. Overall, the unconstrained scenarios produced smaller median ETp changes from historical baseline conditions, with a smaller range of outcomes than those driven by GCM-directed scenarios. Collectively, the range of annual and growing season ET changes from baseline estimates in response to the unconstrained climate scenarios was +10% to +40%. No outlier responses were identified. ETp changes driven by GCM-directed (constrained) UKMO radiation and humidity scenarios were on the order of +100%, resulting in the identification of some ETp responses as statistical outliers. These response differences were attributed to differences between the constrained and unconstrained humidity scenarios.

Development of Regional Climate Scenarios Using a Downscaling Approach

As the debate on potential climate change continues, it is becoming increasingly clear that the main concerns to the general public are the potential impacts of a change in the climate on societal and biophysical systems. In order to address these concerns researchers need realistic, plausible scenarios of climate change suitable for use in impacts analysis. It is the purpose of this paper to present a downscaling method useful for developing these types of scenarios that are grounded in both General Circulation Model simulations of climate change, and in situ station data. Free atmosphere variables for four gridpoints over the Missouri, Iowa, Nebraska, Kansas (MINK) region from both control and transient simulations from the GFDL General Circulation Model were used with thirty years of nearby station data to generate surface maximum and minimum air temperatures and precipitation. The free atmosphere variables were first subject to a principal components analysis with the principal component (PC) scores used in a multiple regression to relate the upper-air variables to surface temperature and precipitation. Coefficients from the regression on station data were then used with PC scores from the model simulations to generate maximum and minimum temperature and precipitation. The statistical distributions of the downscaled temperatures and precipitation for the control run are compared with those from the observed station data. Results for the transient run are then examined. Lastly, annual time series of temperature for the downscaling results show less warming over the period of the transient simulation than the time series produced directly from the model.

The initial evolution of a buoyant plume

The dynamics of river plumes in a stratified non-tidal sea is considered on the basis of a linear analytical theory and simulations with a numerical primitive equations model based on the GFDL-general circulation model with free surface. The response to an onset of river runoff consists basically of two parts: The formation of a freshwater bulge right in front of the river mouth and the set up of a coastal current by Kelvin waves. The properties of the Kelvin waves depend on the stratification of the sea. For an unstratified sea the baroclinic Kelvin wave modes are missing and the spreading of the river water is mainly confined to the near field and a slow alongshore propagation of the freshwater, while for a stratified sea the baroclinic Kelvin waves propagate alongshore and establish the far field response. After about 15–20 days of simulation time a secondary bulge develops downstream. A clue for the understanding of the plume structure is the weakly nonlinear effect due to the changes of the stratification by the spreading of the buoyant freshwater. If wind forcing is taken into account, the plume pattern is strongly affected by the on- or off-shore Ekman transport.

The steric component of sea level rise associated with enhanced greenhouse warming: a model study

Climate change due to enhanced greenhouse warming has been calculated using the coupled GFDL general circulation model of the atmosphere and ocean. The results of the model for a sustained increase of atmospheric carbon dioxide of 1% per year over a century indicate a marked warming of the upper ocean. Results of the model are used to study the rise in sea level caused by increase in ocean temperatures and associated changes in ocean circulation. Neglecting possible contributions due to changes in the volume of polar ice sheets and mountain glaciers, the model predicts an average rise in sea level of approximately 15 ± 5 cm by the time atmospheric carbon dioxide doubles. Heating anomalies are greatest in subpolar latitudes. This effect leads to a weakening of the ocean thermohaline circulation. Changes in thermohaline circulation redistribute heat within the ocean from high latitudes toward the equator, and cause a more uniform sea level rise than would occur otherwise.

Comparison of the UKMO and GFDL GCM climate projections in NPP simulations for southern loblolly pine stands

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 07:55-69 (1996) - DOI: https://doi.org/10.3354/cr007055 Comparison of the UKMO and GFDL GCM climate projections in NPP simulations for southern loblolly pine stands Sampson DA, Cooter EJ, Dougherty PM, Allen HL We used the process model BIOMASS version 13.0 to simulate contemporary net primary production (NPP) and NPP response to climate projections for a doubling of atmospheric CO2 concentration from 2 general circulation models (GCMs) that vary in their CO2 sensitivity: the less sensitive GFDL and the more sensitive UKMO. Increased GCM sensitivity to CO2 is reflected in increased predictions in the magnitude, variation, and range of the climate variables. Simulations used a 40 yr historical climate record, and 2 stand and site conditions to standardize the total NPP response estimates for eighteen 1×1° grid cells across the southern United States. Contemporary NPP and NPP response estimates from the 18 cells were smoothed using a cell search algorithm to obtain an NPP response index matrix for the entire loblolly pine (Pinus taeda) forest-type. We conducted a sensitivity analysis of the environmental variables projected to change in a 2×CO2 environment to help interpret simulation output. Contemporary NPP varied from 2.5 to 8.5 Mg C ha-1 yr-1 over the range of loblolly pine. High leaf area index (LAI) simulations had 1.5 to 2 times the productivity of low LAI simulations, but the regional patterns were similar; NPP was correlated with regional differences in precipitation and temperature. The NPP response to future climate and atmospheric changes depended on the GCM used, and on the stand and site condition assumed. Inter-annual estimates for the 18 cell simulations resulted in a +22 to +84% NPP response for the GFDL climate projections and a -30 to +94% NPP response for the UKMO climate projections. The 40-year average NPP response for the smoothed data ranged from +43 to +65% and -1 to +94% for the GFDL and the UKMO climate projections, respectively. Consequently, the magnitude and range of the 40-year average NPP response to the climate projections was directly correlated with the GCM CO2 sensitivity. Although increased CO2 sensitivity resulted in broader extremes in the predicted temperature response, precipitation response for the 2 models was similar. The NPP response was also correlated with the patterns in predicted climate change, with regional differences coupled to local climatic conditions. Climate projections from both models produced similar NPP responses when predicted temperatures and precipitation regimes were similar. Elevated ambient CO2 had a greater effect on NPP response than temperature or precipitation in the sensitivity comparisons. Simulations indicate that a CO2 fertilizer effect, assuming no CO2 acclimation, more than compensates for declines in productivity over most of the loblolly pine forest-type associated with projected decreased precipitation and/or projected low to moderate increases in temperature and, therefore, increased maintenance respiration costs. Loblolly pine · GCM · UKMO · GFDL · Climate change Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 07, No. 1. Publication date: August 22, 1996 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 1996 Inter-Research.

Impact of Climate Change on Maize Yield in Central and Northern Greece: A Simulation Study with Ceres-Maize

The potential impacts of climate change on the phenology and yield of two maize varieties in Greece were studied. Three sites representing the central and northern agricultural regions were selected: Karditsa, Naoussa and Xanthi. The CERES-Maize model, embedded in the Decision Support System for Agrotechnology Transfer (DSSAT 3.0), was used for the crop simulations, with current and possible future management practices. Equilibrium doubled CO2 climate change scenarios were derived from the GISS, GFDL, and UKMO general circulation models (GCMs); a transient scenario was developed from the GISS GCM transient run A. These scenarios predict consistent increases in air temperature, small increases in solar radiation and precipitation changes that vary considerably over the study regions in Greece. Physiological effects of CO2 on crop growth and yield were simulated. Under present management practices, the climate change scenarios generally resulted in decreases in maize yield due to reduced duration of the growing period at all sites. Adaptation analyses showed that mitigation of climate change effects may be achieved through earlier sowing dates and the use of new maize varieties. Varieties with higher kernel-filling rates, currently restricted to the central regions, could be extended to the northern regions of Greece. In the central regions, new maize varieties with longer grain-filling periods might be needed.

GCM Simulations of the Three-Dimensional Propagation of Stationary Waves

Abstract Plumb's formulation of the stationary wave activity flux is used to determine how well versions of the GFDL and NCAR general circulation models simulate the sources, sinks, and horizontal propagation of atmospheric stationary waves, which play an important role in determining regional climate. The wave activity flux provides insight into the simulation of nondynamic as well as dynamic processes in these models. Model performances for current climate simulations are evaluated with respect to NMC analyses averaged over 1978–1990. The models fare best when the stationary wave forcing is strongest, that is, in the wintertime Northern Hemisphere, where they reproduce the observed three-branch structure of upward wave activity flux. For the Northern Hemisphere summer and the Southern Hemisphere in both summer and winter, the models show less agreement with observations, although they do simulate the generally downward flux observed during Northern Hemisphere summer, which the analysis suggests is cause...

Rossby wave propagation into the tropics in two GFDL general circulation models

During the northern winter the eastern Pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres. Theoretical and simple modeling studies suggest that such a region should favor the penetration of Rossby waves into the tropics from higher latitudes. Observational results by Kiladis and Weickmann using 200 mb data indicate that Rossby waves do indeed propagate freely into the tropical eastern Pacific during the northern winter from the Asian jet exit region. They also confirmed that cross-equatorial dispersion of energy from the Northern into the Southern Hemisphere occurs frequently. The present study examines these interactions in climatological runs of two GFDL GCMs. The northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical Pacific. Despite the relative weakness of the Asian jet and wave activity with respect to observations, propagation of Rossby waves into the tropics is present in both models, and these waves are strongly positively tilted as seen in the observations. A momentum budget of the zonal wind and E vector diagnostics over the tropical Pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models.

Rossby wave propagation into the tropics in two GFDL general circulation models

Rossby wave propagation into the tropics in two GFDL general circulation models

A comparison of GCM-simulated and observed mean January and July precipitation

A high-resolution global precipitation climatology (developed by Legates and Willmott) is used to evaluate the simulated January and July precipitation fields of the GFDL, OSU, GISS and UKMO general circulation models (GCMs). Legates and Willmott's climatological estimates were derived from raingage observations and the gage biases were minimized. These estimates are spatially averaged to the resoltuion of each GCM and differences between the GCM-simulated field and the climatological averages are computed and mapped. Zonal averages for ten-degree bands also are examined. Precipitation rates along the Intertropical Convergence Zone (ITCZ) simulated by all four GCMs are considerably lower than the climatological estimates in both months. Moreover, inadequate representation of the seasonal migration and latitudinal extent of the ITCZ result in an underestimation of wet-season precipitation and an overestimation of dry-season rainfall. In the Southern Hemisphere, the January mid-latitude maximum is inadequately simulated and it is overestimated in July. Northern Hemispheric patterns generally are better simulated than those in the Southern Hemisphere. The spectrally-based GFDL model substantially overestimates polar precipitation while it is more accurately represented by the grid-point GCMs. Regional errors are commonly quite large (in many areas they exceed 2 mm day −1) which suggests cautious use of current-generation GCM prognostications for local- or regional-scale climate change studies.

A comparison of GCM-simulated and observed mean January and July precipitation

A high-resolution global precipitation climatology (developed by Legates and Willmott) is used to evaluate the simulated January and July precipitation fields of the GFDL, OSU, GISS and UKMO general circulation models (GCMs). Legates and Willmott's climatological estimates were derived from raingage observations and the gage biases were minimized. These estimates are spatially averaged to the resoltuion of each GCM and differences between the GCM-simulated field and the climatological averages are computed and mapped. Zonal averages for ten-degree bands also are examined. Precipitation rates along the Intertropical Convergence Zone (ITCZ) simulated by all four GCMs are considerably lower than the climatological estimates in both months. Moreover, inadequate representation of the seasonal migration and latitudinal extent of the ITCZ result in an underestimation of wet-season precipitation and an overestimation of dry-season rainfall. In the Southern Hemisphere, the January mid-latitude maximum is inadequately simulated and it is overestimated in July. Northern Hemispheric patterns generally are better simulated than those in the Southern Hemisphere. The spectrally-based GFDL model substantially overestimates polar precipitation while it is more accurately represented by the grid-point GCMs. Regional errors are commonly quite large (in many areas they exceed 2 mm day −1) which suggests cautious use of current-generation GCM prognostications for local- or regional-scale climate change studies.

Observed and Simulated Energy Cycles in the Frequency Domain

Abstract The analysis of spectral energetics in the frequency domain has been applied to several observed datasets and those simulated by a GFDL general circulation model. There exists good agreement on the directions of energy flows between the observed and the simulated atmospheres. The conversion from available potential energy to kinetic energy in the tropics and extratropics is the major source of eddy kinetic energy for all the low and high frequency bands discussed. The energy balance in the tropics has quite different characteristics from those in the extratropics. Instead of an up-scale decascade as in the case of the extratropics, kinetic energy is transferred in an opposite sense, namely from transients of longer time scales to those of shorter time scales. Using a 5-year dataset from the ECMWF operational analysis, an energy cycle is obtained that is in general agreement with the one computed using the data of the FGGE year alone. The interannual variability of the spectral estimates is relati...

Tropical Intraseasonal Oscillations Appearing in a GFDL General Circulation Model and FGGE Data. Part II: Structure

Abstract Space-time spectral and filter analyses are made of the structure of the tropical intraseasonal oscillations appearing in a GFDL 30-wavenumber spectral general circulation model and the FGGE IIIb data set. The model's tropical zonal velocity exhibits spectral peaks with periods of 40–50 and 25–30 days at wavenumber 1 for six individual years, although the 40–50 day peak is not as pronounced as that found in the FGGE dataset. Both the eastward moving 40–50 and 25–30 day oscillations take the form of a Kelvin–Rossby wave pattern in the upper troposphere and a Rossby mode in the lower troposphere. They also take the form of a latitudinally tilted Walker cell which is modified by a meridional convergence in the boundary layer.

Tropical intraseasonal oscillations appearing in a GFDL general circulation model and FGGE data : Hayashi, Y. and D.G. Golder, 1986. Part I. Phase propagation. J. atmos. Sci., 43(24):3058–3067. GFD/NOAA, Princeton Univ., Princeton, NJ 08542, USA

Tropical intraseasonal oscillations appearing in a GFDL general circulation model and FGGE data : Hayashi, Y. and D.G. Golder, 1986. Part I. Phase propagation. J. atmos. Sci., 43(24):3058–3067. GFD/NOAA, Princeton Univ., Princeton, NJ 08542, USA

Tropical Intraseasonal Oscilations Appearing in a GFDL General Circulation Model and FGGE Data. Part I: Phase Propagation

Abstract Space-time spectrum and filter analyses are made of the tropical intraseasonal osciliations in the northern summer appearing in a GFDL 30-wavenumber spectral general circulation model and the FGGE IIIB data. The model exhibits major and minor wavenumber 1 spectral peaks in the equatorial zonal velocity at eastward moving periods of 40–50 and 25–30 day oscillations are associated with a similar spatial structure. In particular, both of these oscillations exhibit a phase reversal between the 200 and 800 mb zonal velocities. They propagate eastward with a node near the dateline and an antinode in the western hemisphere. Their wave patterns take the form of an eastward-moving Kelvin mode near the equator and an eastward-moving Rossby mode away from the equator. Both spectral peaks are also detectable in the model's precipitation, corresponding to those in the observed outgoing longwave radiation. The 40–50 and 25–30 day precipitation oscillations are in phase with the vertical velocity and propagate ...

The Structure and Propagation of Intraseasonal Oscillations Appearing in a GFDL General Circulation Model

The 12-year output of a 15-wavenumber GCM experiment is analyzed, with the objective of describing the spatial and temporal behavior of dominant intraseasonal variations. The parameters analyzed include five-day averages of wind, geopotential height, sea level pressure, and precipitation. It is demonstrated that the spatial structure, propagation characteristics, and seasonal dependence of the model features are consistent with observations reported in the literature. The model findings are interpreted in terms of the current theoretical understanding of tropical and extratropical motions.