U.S. Dept. of Commerce / NOAA
/ OAR / ERL
/ GFDL 
*Disclaimer
U.S. Dept. of Commerce / NOAA
/ OAR / ERL
/ GFDL
*Disclaimer
HIGHLIGHTS OF FY98
and
IMMEDIATE OBJECTIVES
In this section, some research highlights are listed that may be of interest to those persons less concerned with the intricate details of GFDL research. Selected are items that may be of special significance or interest to this wider audience.
Most of the items in this section have been ordered according to the current NOAA Strategic Plan Elements, which are divided roughly according to time scale:
Recognizing that much scientific progress has application to phenomena at a wide variety of scales, a number of items have been placed into a category which cuts across the time scales represented by the previous elements:
This avoids an awkward force-fit of certain topics into a particular time scale and highlights the fundamental role that these topics play as building blocks for progress in multiple research areas.
Note that the categories described above are organized rather differently than the GFDL research project areas presented in the main body of the report. This is but another reflection of the variety and interplay of activities within such a fertile research environment. As an aid in cross-referencing, the number in parentheses following each highlight refers to sections in the main body of the report.
The
need for short-term warning and forecast products covers a broad spectrum
of environmental events which have lifetimes ranging from several minutes
up to a month or so. Some examples of these events are tornadoes, hurricanes,
tsunamis, and coastal storms, as well as "spells" of unusual
weather (warm, cold, wet, or dry). Benefits of these products can be measured
in terms of lives saved, injuries averted, and expenses spared. NOAA's
vision for improvement in this area involves operational modernization
and restructuring, strengthening of observing and prediction systems, and
improved applications and dissemination of products and services.
Efforts
at GFDL are centered around the development of numerical models which may
be used in the prediction of "short-term" atmospheric and oceanic
phenomena. Simulations from these models are studied and compared with
observed data to aid in the understanding of the processes which govern
the behavior of the various phenomena.
With
regard to tropical weather systems, efforts are aimed at the genesis, growth,
and decay of tropical storms and hurricanes. In extratropical regions,
interest includes the development of severe weather systems, the interaction
of medium-scale atmospheric flow with that on larger scales, and the influence
of the underlying topographic features. Experimental prediction of regional-scale
weather parameters weeks to months in advance is being pursued; included
in this context is the study of "ensemble forecasting." With
regard to the marine environment, forecasts of coastal conditions on a
day-to-day basis can be made by coupling of ocean and atmosphere models.
Ocean models are also used to simulate coastal bays and estuaries, the
response of coastal zones to transient atmospheric storms, and Gulf Stream
meanders and rings.
ACCOMPLISHMENTS FY98
Studies
of the energy budget of idealized models of radiative-convective equilibrium
with resolved moist convection have shown that the dominant source of frictional
dissipation in precipitating atmospheres is not the traditional cascade
of energy to small scales, but occurs instead in the immediate vicinity
of falling hydrometeors. In the global atmosphere this mechanism is estimated
to dissipate 1.5 W/m2, which is comparable
to classical estimates of the rate of energy loss from the large-scale
atmospheric circulation in the planetary boundary layer (2.2.3).
The
GFDL Hurricane Prediction System was upgraded in the 1998 hurricane season.
Based on positive test results, the asymmetry of the forecast storm at
12 hours from the preceding forecast cycle is now utilized in the initial
storm specification (6.2.3).
Commitment
to the WMO-cosponsored COMPARE project was completed with successful application
of the GFDL system to the preparation of the initial conditions for a typhoon
case study (6.4).
A
recently completed study of cyclone wave activity confirms its importance
in shaping the large-scale quasi-stationary circulation. It also provides
a clear picture of the month-to-month evolution of the storm track during
the transition from fall to winter. Consistent with these results, this
study also describes the relationship between interannual variability and
the ENSO cycle. This may have important implications for the trajectories
of winter storms entering the North American continent and improving forecast
skill during these events (7.1).
A
series of numerical experiments has focused on the life cycle of cyclone-scale
eddies in realistic storm track environments. Preliminary analyses of cyclone-scale
eddy forcing show encouraging similarities between the velocity correlations
that maintain the isolated ridge in the model simulations and the wintertime
ridge in the eastern Pacific. These simulations have clarified the mechanisms
that predominate in the life cycle of eddies which eventually break anticyclonically,
the precursor of establishing the quasi-stationary ridge. This process
is strongly interactive since it is the trough-ridge system itself that
limits the life cycle of these eddies (7.2).
The
hydrostatic terrain-following Zeta model has been used extensively in the
ICTP Summer Colloquium on the Physics of Weather and Climate entitled "The
Effect of Topography on the Atmospheric Circulation". One outgrowth
of this is that the ZETA model is being run at a number of sites worldwide
for investigating a wide variety of atmospheric flows (7.4).
PLANS FY99
The GFDL hurricane model will be improved by increasing the grid resolution
of multiply nested meshes. The improved representation of the eye and eyewall
of intense hurricanes, as well as of the large-scale environmental flow,
should improve both the skill of the GFDL Hurricane Prediction System and
accuracy of simulations for numerical research.
A new methodology will be developed for the initialization of hurricane
models in which the initial vortex will be one which is compatible with
the environmental conditions. Also, the new scheme will be better able
to ingest various types of available data from other observations/analyses.
The ongoing investigation into the interaction between cyclone wave activity
and the large-scale quasi-stationary circulation will be extended to the
Southern Hemisphere. Variations in cyclone development at the entrance
of the Atlantic-Indian Ocean storm track during the warm and cold phases
of the ENSO cycle will be examined. Extended numerical simulations of storm
tracks will focus on the mechanisms responsible for the growth, maintenance,
and dissipation of the quasi-stationary features in idealized storm tracks.
Numerical simulations of storm tracks will assess the sensitivity of cyclone
evolution to its position within the storm track. In particular, the mechanisms
responsible for the poleward progression of low-level eddies and the equatorward
progression of upper-level eddies will be further analyzed. The role of
cyclone-scale eddies in the growth, maintenance, and dissipation of the
quasi-stationary features in idealized storm tracks will continue to be
evaluated.
The development of limited area models will emphasize the incorporation
of moist physics and boundary layer processes into the new, high resolution
anelastic hydrostatic and non-hydrostatic models.
Seasonal
to interannual climate fluctuations have far-reaching consequences for
agriculture, fishing, water resources, transportation, energy consumption,
and commerce, among others. Short-term climate anomalies which persist
from a season to several years affect rainfall distributions, surface temperatures,
and atmospheric and oceanic circulation patterns. Reliable climate forecasts
may be used to reduce the disruption, economic losses, and human suffering
that occur in connection with these anomalies. NOAA's vision for improvement
in this area is based on better predictive capability, enhanced observations,
greater understanding of climate fluctuations, and assessment of impacts.
The
study of seasonal to interannual climate fluctuations at GFDL is based
on both theoretical and observational studies. Available observations are
analyzed to determine the physical processes governing the behavior of
the oceans and atmosphere. Mathematical models are constructed to study,
simulate, and predict the coupled ocean-atmosphere, land-surface, sea-ice
system.
Simulations
based on the numerical models maintained at GFDL, in conjunction with observations,
are used to study climate variations on seasonal and longer time scales.
Processes under study include large-scale wave disturbances and their role
in the general circulation, the effects of boundary conditions such as
sea surface temperature and soil moisture, influence of clouds, radiation,
and atmospheric convection, and the "teleconnection" of atmospheric
anomalies across the global atmosphere. Furthermore, experimental model
forecasts are used to evaluate atmospheric predictability and to assess
skill in forecasting atmospheric and oceanic climate anomalies, both in
general and in connection with the El Niño-Southern Oscillation
phenomenon. Also, a more accurate representation of the state of the global
ocean is being studied through data assimilation for better initialization
of seasonal-interannual forecasts.
ACCOMPLISHMENTS FY98
The
tropical intraseasonal oscillations in the R30 atmospheric model have been
shown to be very sensitive to the inclusion of a cloud prediction scheme,
with some of the effects due to direct interaction of clouds with the oscillation
and some due to the change in the structure of the mean tropical atmosphere
(1.7.2).
Considerable progress has been made on developing a flexible system for
general circulation modeling. Two atmospheric dynamical cores, a B-grid
and a spectral model, are essentially complete. Both models have been tested
with the same modular physical parameterizations. A flexible framework
for coupling component models with arbitrary grids is under development
and has been used to create coupled atmosphere-ocean-ice-land surface models
(3.1).
A
hybrid coupled model with a statistical atmosphere coupled to the MOM ocean
general circulation model has been developed. This model provides a powerful
and relatively inexpensive framework in which to investigate the impacts
of changes to the details of the ocean model. It also provides a good benchmark
against which to measure the abilities of more comprehensive coupled prediction
models (3.2.2).
A
large coupled model ensemble prediction experiment has been conducted to
facilitate the investigation of an array of problems in seasonal/interannual
prediction and predictability. A set of six 19-year atmospheric simulations
and corresponding sets of one year lead coupled model predictions has been
produced and formatted for easy analysis (3.3.1).
A series of atmosphere-only GCM simulations has been used to explore the
causes of interannual and interdecadal variations in the number of tropical
storms over the Atlantic Ocean. On interannual timescales, the primary
cause appears to be the impact of tropical Pacific SSTs through an indirect
pathway via a modified large-scale atmospheric circulation. On interdecadal
timescales, the local tropical Atlantic SST seems to be the major factor
impacting the number of Atlantic tropical storms (3.3.2).
A
Monte Carlo implementation of a non-linear filter for ensemble data assimilation
has been greatly improved. The method has been tested in a variety of low-order
models and produced high quality stochastic analyses. Initial tests in
global barotropic models suggest that the method may be successfully extended
to realistic general circulation models (3.4.1).
An
extended suite of experiments on the atmospheric response to sea surface
temperature (SST) anomalies in different parts of the World Oceans has
been completed using a R30, 14-level climate GCM. This project represents
a major commitment of GFDL to the simulation of climate variability using
higher-resolution GCMs. The performance of the R30 model is much improved
over the earlier R15 version in many respects, including the generation
of more realistic precipitation anomalies in response to tropical SST changes,
more energetic transient eddies in the middle latitudes, and stronger teleconnections
between ENSO-related SST anomalies and the extratropical atmospheric circulation
(5.4.1, 5.4.2).
A
GCM experiment with interannual SST variations prescribed in the tropical
Pacific and with SST changes outside of this forcing region being predicted
by a simple mixed-layer ocean model has been analyzed. The results indicate
that the remote atmospheric response to the SST anomalies in the tropical
Pacific exerts a notable influence on the SST variability in the North
Pacific, a large portion of the Atlantic Basin, and parts of the Indian
Ocean. These findings illustrate that the "atmospheric bridge"
linking the ENSO region with other parts of the World Oceans is an important
contributor to variability of the coupled system on interannual timescales.
Considerable agreement exists between the air-sea interactions simulated
in this experiment and those inferred from observations (5.4.2).
Satellite
observations of temperature, water vapor, precipitation and outgoing longwave
radiation have been used to characterize the variation of the tropical
hydrologic and energy budgets associated with ENSO. Atmospheric global
climate models, forced with observed sea-surface temperatures, accurately
reproduced the observed tropospheric temperature, water vapor and outgoing
longwave radiation changes. However, the predicted variations in tropical-mean
precipitation rate were substantially smaller than observed. The comparison
suggests that either the sensitivity of the tropical hydrological cycle
to ENSO-driven changes in SST is substantially underpredicted in existing
climate models, or that current satellite observations are inadequate to
accurately monitor ENSO-related changes in the tropical-mean precipitation
(5.2.1).
PLANS FY99
Modifications to the R30 coupled model will be made, concentrating on a
smoother initialization and improved tropical intraseasonal variability.
A control integration and various scenario integrations will be initiated
with this improved version of the model.
Complete coupled atmosphere-ocean-ice-land surface models will be constructed
in the context of the flexible modeling system. These models will be tested
for both climate and seasonal/interannual prediction purposes.
The newly developed hybrid coupled model will be used to investigate the
impact of details of the ocean model on seasonal/interannual prediction.
Stochastic forcing will be added to the hybrid model in an attempt to determine
the impact of atmospheric noise on the coupled system's dynamics.
The results of the coupled model ensemble prediction experiment will be
analyzed by a number of scientists within GFDL and by members of the GFDL
University Consortium. In particular, forecast skill and potential skill
will be examined for both tropical and extratropical fields.
The Monte Carlo non-linear filter data assimilation technique will be applied
to the flexible B-grid dynamical core model. If this is successful, further
extension to a B-grid model version with realistic physics will be undertaken.
Multiple experiments with the atmospheric climate GCM coupled to a new
mixed-layer ocean model with variable depth will be performed. Particular
attention will be devoted to the simulation of the atmospheric and oceanic
processes associated with the atmospheric bridge mechanism linking ENSO
with SST changes throughout the World Oceans, and the nature of the recurrence
of extratropical SST anomalies in consecutive cold seasons.
The simulated atmospheric circulation changes associated with SST anomalies
prescribed in the tropical Atlantic will be analyzed. The mechanisms for
the air-sea coupling over the Atlantic will be critically examined using
the model output, with special emphasis on the nature of local interactions
between the wind field and the underlying SST anomaly, as well as the remote
midlatitude atmospheric response to tropical Atlantic SST forcing.
The relationship between upper tropospheric water vapor and the tropical
circulation will be examined on diurnal and seasonal time scales using
hourly satellite observations. A tracking algorithm will be applied to
analyze the spatial displacement of the patterns of pixel-resolution GOES
total precipitable water. Such an application will be used to study the
role of moisture transport from the Caribbean Basin and eastern tropical
Pacific on precipitation variability over the U.S.
Events
such as the Sahel drought, the dust bowls in the Midwest, the Little Ice
Age, stratospheric ozone depletion, and global warming may define eras
in history. Events such as these have lifetimes of decades to centuries
and their causes may be either natural or anthropogenic. An ability to
predict such changes and to assess the causes is essential in long-range
policy making. Adapting to these changes and reducing the effects of human
activities will require enhanced predictive capability. NOAA's vision for
improvement in this area is based on a commitment to research in climate
and air quality, as well as to insure long-term climate and chemical records.
The
related research efforts at GFDL require judicious combinations of theoretical
models and specialized observations. The modeling efforts draw on principles
from the atmospheric, oceanic, chemical, and biological sciences. One area
of focus is long-term climate variability and secular change associated
with the atmosphere and oceans. This area encompasses a number of topics,
including the effects of changes in the concentration of atmospheric gases
such as carbon dioxide, the simulation of past climates, and the variability
of the oceanic thermohaline circulation. Another area of focus is the formation,
transport, and chemistry of atmospheric trace constituents. This area addresses
problems such as: the transport of quasi-conservative trace gases; the
biogeochemistry of climatically significant long-lived trace gases; the
transport, sources, and sinks of aerosols; the chemistry of ozone and its
regulative trace species; the effects of clouds and aerosols on chemically
important trace gases; and the impact of anthropogenic chlorofluorocarbons
on stratospheric ozone amounts. Yet another area of focus relates to the
modeling of the marine environment. It includes the dispersion of geochemical
tracers in the world oceans, the oceanic carbon cycle and trace metal geochemistry,
and ecosystem structures.
ACCOMPLISHMENTS FY98
A
400-year control integration with a stable climate has been generated with
a medium resolution (R30) coupled atmosphere-ocean climate model. The model
produces very active ENSO-like variability. The first CO2+aerosol
scenario integrations with this model are under analysis. Global warming
occurs at roughly the same rate as in earlier lower resolution studies
(1.3.1).
A
10,000 year control integration of the low resolution, R15 model has been
completed which allows climatic variability on time scales up to 1,000
years to be studied. The model generates a singular cooling event in the
North Atlantic of several decades duration that is larger in amplitude
by a factor of two than any other such events in the entire 10,000 years
integration. This result underlines the need for such long integrations
in the study of natural climatic variability (1.4.1).
The
existence of two stable, climatic equilibria - one with an active Atlantic
thermohaline overturning and one in which this overturning is weak and
reversed - has been confirmed using a new version of the coupled model.
The climate with a weak reversed overturning circulation does not exist
if the vertical diffusivity in the model is increased (1.4.2).
An
ensemble of nine C02+aerosol scenario integrations of global warming has
been completed with the R15 low resolution coupled model. This ensemble
has been used to study the emergence of climatic signals from the model's
natural variability and to determine the distortions caused by starting
the integrations in the late 19th or early 20th centuries, rather than
in the pre-industrial era (1.4.3).
The
behavior of the R15 coupled model has been simulated by forcing the ocean
model in isolation with stochastic heat and freshwater fluxes. Studies
of the model's interdecadal variability in the North Atlantic have shown
that this variability is not due to coupled air-sea modes, and that the
heat fluxes are of greater importance than the freshwater fluxes in generating
the coupled model's interdecadal oscillations (1.4.7).
A
study of river discharge statistics generated by the R15 CO2+aerosol
scenario integrations suggests that increased frequency of major floods
should become significant by the year 2020, but is undetectable at present
(1.5.2).
A
study with an atmospheric GCM coupled to a mixed layer ocean in the tropics,
but with specified surface temperatures in the extratropics, has shown
that the effect of cooling in the extratropics of one hemisphere, with
respect to the extratropics of the other hemisphere, has a very large effect
on the tropical Hadley circulation and the position of the intertropical
convergence zone (1.6.1).
A
test has been devised, using atmospheric data, to evaluate a method for
estimating the diffusivity due to mesoscale eddies in the ocean from altimeter
measurements of sea level variability. The results suggest that this method
is reliable, implying that altimeter data can be used to constrain eddy
flux closure schemes in ocean models (1.7.3).
Sulfate
chemistry and transport have been modeled in a high-resolution cloud-system
model. Vertical transport of sulfur, nucleation scavenging, and aqueous
oxidation result in appreciable sulfate concentrations in upper-tropospheric
ice clouds. The presence of sulfate in these clouds alters both their shortwave
and longwave radiative properties, exerting an indirect aerosol effect.
Earlier studies of indirect effects have focused mostly on boundary-layer
clouds and shortwave effects, so these results draw attention to new issues
in the cloud-climate problem (2.2.2).
Studies
with the cloud-system model have also shown that treatment of ice microphysics
and ice radiative transfer plays a central role in both top-of-atmosphere
and surface cloud forcing by these systems. Recent observations of the
surface radiation balance in the equatorial western Pacific have made possible
an evaluation of these important aspects of the cloud-convection-radiation
problem (2.2.2).
Simulations
of global tropospheric NOx by the GFDL
Global Chemical Transport Model (GCTM) quantitatively capture the observed
latitudinal, vertical and seasonal behavior. Detailed analyses of individual
natural and anthropogenic sources find that: a) lightning, the primary
natural source, dominates in the upper half of the tropical and summertime
extratropical troposphere; b) anthropogenic emissions from fossil fuel
combustion and biomass burning dominate in the lower half of the troposphere;
and c) aircraft emissions have a significant impact on the upper troposphere
of the Northern Hemisphere extratropics (2.3.4).
A
three-tracer simulation of tropospheric ozone with the GFDL GCTM finds
that ozone produced in the background troposphere accounts for 54% of the
global tropospheric budget, while ozone transported from the stratosphere
accounts for 38%. Ozone directly produced by the complex hydrocarbon photochemistry
of the polluted boundary layer plays a minor role outside of that region
and only contributes 8% of the global budget (2.3.5).
A
control integration using a version of the SKYHI model at 0.33
x 0.4 resolution
has continued for over six months. The simulation of the zonal-mean circulation
in the extratropical middle atmosphere in this model has been found to
be quite realistic over most of the year, even without the inclusion of
any parameterized drag on the mean flow (2.4.2). The horizontal spectrum
of kinetic energy in this model has been analyzed and found to agree well
with available observations (2.4.5).
Simulations
using the SKYHI model with enhanced vertical resolution (less than 1 km
grid spacing in the stratosphere) display long-period oscillations in the
tropical stratospheric mean winds with properties very similar to the observed
quasi-biennial oscillation. This represents encouraging progress on a long-standing
problem with first-principles simulations of the middle atmospheric circulation
(2.5.3).
A
long integration has been performed using a moderate-resolution version
of the SKYHI model and including a sophisticated treatment of ozone photochemistry.
The model displays considerable interannual variability in the circulation
and in ozone concentrations. Particularly interesting is the appearance
of significant long-period (decadal or longer) variations in the Northern
Hemisphere midlatitudes. These appear with prescribed, seasonally varying
SSTs and in the absence of external forcing (such as anthropogenic chemical
release, volcanic aerosols, solar variability, etc.) and are apparently
driven by internal atmospheric dynamics (2.4.9).
Temperature
trends in lower stratosphere are broadly consistent among different datasets,
ranging from radiosonde and satellite measurements to analyzed fields.
This is particularly so in the midlatitude Northern Hemisphere. Model simulations
indicate that the cooling of the lower stratosphere at nearly all latitudes
is a consequence of the global ozone depletion (2.5.1).
A
simulation of the atmospheric distribution of carbonaceous aerosols from
a specified distribution of source strengths has been performed using the
SKYHI GCM's tracer transport capability. The aerosols are transported well
away from the source regions, both horizontally and vertically. Comparisons
with NOAA/CMDL's surface observations at Sable Island and Bondville indicate
that the seasonal simulations at these sites compare reasonably well with
the measurements (2.3.6).
Benchmark
computations reveal that the total solar flux absorbed in overcast atmospheres
differs from that in clear-sky. It depends crucially on cloud type, geometrical
thickness and location. The benchmark results disagree with recent interpretations
from observations concerning both the magnitude and apparent invariance
of cloud absorption. This suggests that either the observational inferences
are incorrect or the known fundamental radiative transfer principles are
at odds with the process in the actual atmosphere (2.1.2).
A
new shortwave radiation parameterization has led to a pronounced improvement
in the simulation of the stratospheric temperatures, primarily due to a
more proper accounting of the solar absorption by CO2.
The warming of the stratosphere due to an increase in the absorption by
CO2 directly alleviates a bias seen in
earlier model simulations when compared against recent satellite observations
(2.1.3).
The
radiative forcing due to tropospheric sulfate (negative) and soot (positive)
aerosols, and tropospheric ozone (positive) all have a geographical distribution
that is maximized near the source regions in the continental midlatitude
Northern Hemisphere. The sum of the forcings due to these three inhomogeneously
distributed species has an interesting cancellation in the global-mean,
but substantial gradients exist on the regional scale, consisting of positive
and negative values, especially in the midlatitude Northern Hemisphere
(2.5.2).
Considerable
progress has been made on developing a flexible system for general circulation
modeling. Two atmospheric dynamical cores, a B-grid and a spectral model,
are essentially complete. Both models have been tested with the same modular
physical parameterizations. A flexible framework for coupling component
models with arbitrary grids is under development and has been used to create
coupled atmosphere-ocean-ice-land surface models (3.1).
A
series of atmosphere-only GCM simulations has been used to explore the
causes of interannual and interdecadal variations in the number of tropical
storms over the Atlantic Ocean. On interannual timescales, the primary
cause appears to be the impact of tropical Pacific SSTs through an indirect
pathway via a modified large-scale atmospheric circulation. On interdecadal
timescales, the local tropical Atlantic SST seems to be the major factor
impacting the number of Atlantic tropical storms (3.3.2).
An
idealized coupled model has been developed which demonstrates that the
Atlantic Ocean's meridional overturning circulation can be initiated simply
by opening Drake Passage. This result suggests that the formation of deep
water in the North Atlantic and the northward heat transport in the Atlantic
Ocean are linked to the Antarctic Circumpolar Current in the high latitudes
of the Southern Hemisphere (4.1.1).
Results
from a new isopycnal-coordinate ocean model indicate that the ocean's density
structure is dynamically consistent with low levels of vertical mixing
in the open ocean. The warming branch of the thermohaline circulation occurs
mainly through wind-driven upwelling in the Southern Ocean and at the equator
(4.1.2).
A
new sea-ice model has been developed for coupled models. Sea-ice motion
in the new model is a product of internal stresses within the ice, in addition
to the motions forced by the wind and underlying ocean currents (4.1.3).
A
new study of terrestrial and oceanic carbon sinks shows that the North
American continent is a significant sink for atmospheric CO2.
The North American terrestrial sink is at least 2/3 of the total terrestrial
sink for the Northern Hemisphere and is comparable in magnitude to fossil
fuel emissions from North America (4.4.1).
The
impact of climate warming on hurricane intensities was investigated using
the GFDL hurricane model embedded in a CO2-induced
warm climate derived from the GFDL climate model. For a sea surface temperature
increase of about 2.2C,
storms in the northwest Pacific basin were stronger by 3-7 m/s for the
surface wind and deeper by 7-20 hPa (6.3.1).
PLANS FY99
Several R30 coupled climate model CO2+aerosol
scenario integrations will be analyzed to assess the robustness of the
climate changes predicted by earlier R15 simulations, with a focus on changes
in oceanic circulation.
An ensemble of R15 scenario integrations will undergo detailed analysis
to study the emergence of a variety of climatic signals from the noise
of natural variability. The number of members in the ensemble will be increased
as needed for this study.
New versions of the coupled model will be used to study various alternative
approaches to the initialization of coupled models for studies of global
warming and natural variability.
The dynamics of the changes in the position and strength of the Southern
Hemisphere surface westerlies, produced in a number of global warming simulations,
will be studied with a hierarchy of models aimed at clarifying the relationships
between changes in meridional temperature gradients and changes in the
zonal mean surface winds.
The R15 atmospheric model, coupled to a mixed layer, will be use to simulate
the last 120,000 years of climate history, as forced by prescribed changes
in orbital parameters, ice sheets, and greenhouse gas concentrations, by
accelerating the evolution of these forcing functions by a factor of 30.
Working within the new GFDL atmospheric modeling structure, a new T42,
30 level model will be coupled to the MOM3 ocean code using the recently
designed coupling software, and tests will be performed on alternative
parameterizations of atmospheric physics. New ice and land surface models
will be incorporated into this structure as well. A T106 version of the
atmospheric model will be developed simultaneously.
New approaches to ice microphysics and radiative transfer will be implemented
in the cloud-system model and evaluated using both surface and top-of-atmosphere
observations of radiative fluxes. This should improve our understanding
of the role of deep convective systems in the coupled ocean-atmosphere
system.
The chemical and transport mechanisms involved in generating interannual
variability in SKYHI ozone photochemistry simulations will be analyzed.
Computations and analyses of solar radiative benchmark computations for
more complex cloud systems, including multi-layered clouds, will be continued.
Additionally, longwave benchmarks will be started, for the purpose of developing
parameterizations for non-gray absorbers in the thermal infrared.
Investigation of the chemistry-transport problem leading to the geographical
distribution of various kinds of aerosols will continue. Plans call for
the simulation of the transport of sulfate aerosols, to be followed by
dust, organics and sea-salt. Also, the problems associated with stratospheric
aerosol distribution following volcanic events will be pursued, and the
accompanying radiative impacts will be evaluated. Climatic effects of radiative
forcing due to non-well-mixed trace gases in the troposphere and stratosphere
will also be investigated.
Aerosol-cloud interactions will continue to be investigated from a host
of microphysically- and chemically-based perspectives, from micro-scale
models to cloud-resolving models to GCMs. Observational data will be utilized
to test and analyze the model simulations.
Convection-cloud-radiation-climate interactions will be pursued using the
cloud resolving model and the laboratory's GCMs. Emphasis will include
examination of available observational data on water vapor, clouds and
the energy budget in order to test, evaluate and develop each of the physical
components that govern these interactions and thus play a role in climate.
Additionally, the influence of these interactions for the maintenance of
present-day climate and for future climate change will be investigated.
Temperature trends in the entire stratosphere (extending to the middle
and upper stratosphere) derived from observational data will be analyzed.
Model simulations will be performed to extend the detection-attribution
investigation to the entire stratosphere. Both natural and anthropogenic
factors will be considered.
Complete coupled atmosphere-ocean-ice-land surface models will be constructed
in the context of the flexible modeling system. These models will be tested
for both climate and seasonal/interannual prediction purposes.
The interannual variability of oceanic and terrestrial CO2
uptake will be studied using a new time-varying inverse model for atmospheric
carbon sinks. An inverse model will also be applied to the study of steady
state fluxes of CO2 and oxygen between
the ocean and atmosphere.
A
number of the research topics at GFDL cut across the various time scales
characteristic of each of the foregoing sections. Progress on these topics
impacts many other research areas which depend critically on the successful
representation of numerous lower-level processes which are common to problems
at all scales. Topics which fall into this category include hydrological
processes, radiative transfer (including the effects of aerosols and clouds),
cloud prediction/specification, "teleconnection" of atmospheric
anomalies across the global atmosphere, satellite data interpretation,
transport processes, gravity wave effects and parameterization, model resolution
effects, and many other model enhancement efforts. As these processes become
better understood and more accurately represented, benefits will accrue
to a multitude of other research efforts.
ACCOMPLISHMENTS FY98
A
tool designed to facilitate conversions of models to scalable parallel
architectures is under development. A version of the flexible spectral
dynamical core has been parallelized using this tool and has demonstrated
reasonable performance on parallel platforms (3.1.1.4).
A
series of experiments with coupled general circulation models identified
a number of shortcomings in the convective and cloud parameterizations
in the experimental prediction models. New versions of the Relaxed Arakawa
Schubert convection scheme in concert with modifications to the cloud parameterization
have led to improved simulations at both the surface and in the upper troposphere
(3.2.1).
A
new version of GFDL's Modular Ocean Model (MOM 3) has been made available
for testing. This version contains an upgrade which allows MOM to be run
efficiently on the next generation of parallel computers (4.2.1).
A
combination of high-resolution numerical and analytical models have been
used to estimate the total mountain drag exerted by the Rocky Mountains
down to horizontal scales of 20 km. For summertime flow conditions, fine-resolution
numerical experiments indicate that most of the momentum flux reaching
the stratosphere is due to linear, hydrostatic gravity waves launched by
the smallest resolved terrain features which occur primarily at the upstream
and downstream edges of the massif. The parameterized subgrid drag and
divergent surface velocity from a coarse resolution experiment are in good
agreement with the high-resolution result (7.3).
PLANS FY99
The
spectral kinetic energy budget in high-resolution SKHYI model simulations
will be analyzed to determine the dominant excitation and dissipation mechanisms.
Such analysis may have implications for designing appropriate subgrid-scale
closure schemes for climate and weather models.
A
scalable version of the flexible spectral dynamical core will be improved
and a scalable version of the B-grid flexible dynamical core will be written.
Work will begin on understanding the problem of parallelizing coupled models.
New
representations of boundary layers at the bottom of the ocean will be implemented
in both z-coordinate and isopycnal coordinate models at GFDL.
GCMs
and limited-area model simulations with very high resolutions and realistic
temporal and spatial variations of the basic flow will be used to test
the linear model of total mountain drag.
*Portions of this document contain material that has not yet been formally published and may not be quoted or referenced without explicit permission of the author(s).