Research Elements
Barron and Jenkins completed a series of control experiments using GENESIS
for the EOS project, including an AMIP simulation with specified seasonally
varying sea surface temperatures (SSTs) from 1979 to 1988, SST climatologies,
a mixed layer ocean experiment, and R15 and T42 versions. Barron and Jenkins
(1994) assessed the GENESIS precipitation over the United States for different
GCM resolution and ocean specifications, noting that the ocean component
(mixed layer versus longitudinal variation in SST) was more significant
in predicting U.S. precipitation than was the difference between R15 and
T42. GCM predictions were found to be inad equate for regional climate evaluations.
A detailed comparison of the results of these experiments is in preparation.
Future research plans include intercomparison of CCM2, advanced GENESIS
and UK Meteorological Office GCM predictions of precipitation, humidity
and temperature structure, comparison of GCM observations with EOS Pathfinder
data and GEWEX global precipitation climatology and completion of base runs
for nested model experiments, focussed neural net analysis of the Susquehanna
River Basin, and incorporation of improved cloud parameterizations in GENESIS.
Many of the experiments described under Objective 1 for different ocean
specifications (AMIP SSTs, climatological SSTs, mixed layer model) and the
results (Barron and Jenkins, 1994) have direct bearing on this goal as well.
Recent experiments at T31 resolution (Robertson et al., 1995a) and the studies
cited above indicate: 1) that tropical SST forcing has a robust quasi-linear
response in the vicinity of the heating - - rainfall, divergent circulations
and radiative anomalies for two El Ninos are well captured by the model,
2) the middle latitude response is characterized by a much lower signal
to noise ratio, 3) warm season, mid-latitude anomalies such as the 1988
drought over the U.S. show significant predictability, and 4) in agreement
with ERBE results, comparison of 1987 and 1988 greenhouse forcing calculations
show some negative water vapor feedback over the tropical Pacific associated
with elevated SSTs and deep convection.
In addition, Dutton and Barron (1995) have completed a series of experiments
for changes in GENESIS land surface vegetation with two purposes, to determine
the significance of vegetation factors in climate and to assess the potential
significance of vegetation changes for future cli mate. These experiments
demonstrate that the greatest sensitivity occurs for changes between low
level vegetation (grasslands and tundra) and multi-storied vegetation, and
between ever green and deciduous forests. Large regional surface temperature
changes (greater than 5 degrees C) and global changes of almost 1 degree C were noted
in association with changes in the distribution of grasses, tundra and forests.
Each of these vegetation types is sensitive to climate change.
Future research will include continued: (1) Use of EOS Pathfinders, including
SSM/I retrievals of vapor, liquid water, precipitating ice, and surface
wind stress and MSU radiances for examining the hydrologic cycle and its
sensitivity, (2) Use of the SSMT/2 water vapor profiling capability to quantify
water vapor feedback, (3) Use of ISLSCP data, with observed precipitation,
and satellite estimates of surface incident solar radiation to synthesize
global soil moisture time series, (4) Completion of the vegetation experiments
for different vegetation classes, leading to a more detailed analysis of
the significance of the vegetation parameters, including the e-folding
time for snow cover, leaf abscission, and the rooting depth of the vegetation.
These experiments will allow a better assessment of the uncertainties and
the significance of specific variables in governing climate-vegetation
sensitivity.
Results reported in Robertson and McCaul (1994), Barrett et al. (1994) and
Cohen and Robertson (1994) have focussed on development of a gridded (2.5
degree resolution, 2 x daily) SSM/I precipitable data product and a unique semi-prognostic
approach for assimilating remotely sensed moisture data. By combining SSM/I
water vapor and ECMWF large scale vertical motions we have derived conservation
equations which link vapor, liquid and ice. As one important demonstration
of this methodology, a consistent vapor and condensate budget for the TOGA-COARE
period has been developed which connects the large-scale divergent circulation
to atmospheric hydrologic processes. These results have a variety of uses,
from providing a 3-D time structure of atmospheric moisture constituents,
to serving as testbeds for convective and cloud parameterizations, and calibrating
microphysical parameterizations which influence the upper tropospheric water
budget. The products are an important contribution to EOS 4-D data as similation
efforts. Additional analyses focussed on examination of the interannual
variability and persistence of soil moisture anomalies in the global model
(Fitzjarrald et al., 1994; 1995).
The analysis of MSU data continues to provide high precision data for climate
studies. To date, over 25 refereed papers have been published for which
the MSU data were the sole or main source of information for the scientific
results. Improvements have been applied as intersatellite variations have
been analyzed due to orbital drift, instrument dynamic range, absolute biases
and missing data. These data are heavily used in assessments of global climate
change. Key results are (1) proof that sequentially-launched polar orbiting
satellites with microwave instruments designed for weather observations
provide sufficient precision to create long-term data sets, (2) the global
temperature of the troposphere has declined at a rate of 0.06 degrees per
decade since 1979, however removal of the effects of El Nino and volcanoes
results in an upward trend of 0.09 degrees per decade since 1979. Latest
results of transient climate model runs (including aerosols) show similar
trends, (3) the last two years have exhibited the coldest lower stratospheric
temperatures on record. A key part of our global climate model simulations
is the fidelity with which the GENESIS GCM reproduces the actual global
temperature distribution and variability. MSU data for 17 years (temperature
and oceanic precipitation) are now available for the variability studies.
Example publications and conference reports which are contributions
from this investigation for 1994 and 1995 include (Christy, 1995; Christy
et al., 1995a,b,c; Balling and Christy, 1995; Christy and Drouilhet, 1994;
Christy and McNider, 1994; Christy and Goodridge 1995; Spencer et al., 1994;
Karl et al., 1994).
Future research emphasis will be on validation of GCM simulations. The inadvertent
positional drift of NOAA-11 has opened up the possibility of identifying
the diurnal cycle of tropospheric and stratospheric temperatures. Effort
will also be focussed on predictive studies on the 10-day to seasonal time
scale.
We have characterized the structure of the marine boundary layer (FIRE,
ASTEX, TIWE) and fractional cloudiness (laser ceilometers) and continental
stratus (using cloud radar, lidar, ceilometers, microwave radiometers)
in order to evaluate and develop cloud parameterizations. Major accomplishments
include: (1) development of a hierarchy of techniques to drive cloud parameterizations
with data, separately from GCM studies, in order to verify GCM cloud and
radiation predictions (Mace and Ackerman, 1995, Mace et al. 1994). This
method allows integration across the scales of GCMs and mesoscale models,
which are central to this EOS investigation. (2) demonstrated the feasibility
of using a simple boundary layer model to provide a regional simulation
of boundary layer structure and fractional cloudiness (with S. Wang and
P. Minnis) (Wang,1994a,b, Wang and Wang, 1994). (3) Modified Tiedke's prognostic
cloud scheme and implemented it in a two-layer boundary-layer model (Wang,
1995). Coupled with a mass flux convective mixing scheme this technique
is a good framework for parameterization of marine boundary layer clouds
in GCMs. (4) Defined the structure of the marine boundary layer over the
past several years over the tropics and subtropics during major field programs
(Albrecht et al., 1995a,b), developing composite soundings which were then
used to evaluate model parameterizations that represent fractional cloudiness
as a function of boundary layer structure. Parameterizations based on the
relative humidity in the cloud layer agree better with observations than
those that account for cloud-top entrainment instability on fractional cloudiness.
These composite data sets are being used to test the boundary layer regional
model for this EOS project, and support the atmospheric and cloud-related
products generated from MODIS and CERES. Additional contributions included
elucidation of cloud structure using radar (Syrett et al., 1994).
Increased emphasis in future research will be placed on continental boundary
layer clouds as characterized using surface-based remote sensors, aircraft
and satellites with the goal of realistically simulating continental temperatures
and annual and diurnal temperature cycles. This will be based on observations
collected during the fall of 1994 and the spring of 1995. We plan to compare
the cloud structure observed from satellites (in cooperation with P. Minnis)
with cloud characteristics obtained from surface based remote sensing, providing
an important framework for utilizing EOS cloud products to infer the characteristics
of continental boundary layer clouds.
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