The following abstracts are for PhD and Master's theses written using global NCAR
climate models since the release of CSM1 in 1996. The list is current through June 2005.
Title: Quantitative paleoclimatic reconstructions for the Late
Quaternary of southern South America based on calibration
of modern pollen and climate relationships
Pub No: 9827679
Author: Anderson, Lysanna
Degree: PhD
School: UNIVERSITY OF COLORADO AT BOULDER
Date: 1998
Pages: 219
Adviser: Markgraf, Vera
ISBN: 0-591-80013-6
Source: DAI-B 59/03, p. 1017, Sep 1998
Subject: GEOLOGY (0372); PALEOECOLOGY (0426); PALYNOLOGY (0427)
Abstract: Three approaches to deriving quantitative estimates of
past temperature and precipitation (multiple regression,
response surfaces, and the method of modern analog) were
evaluated using a modern pollen and climate data set from
southern South America. The results of this analysis show
that, under conditions of sparse climate data, response
surfaces are the most robust approach. The three
calibrated data sets were then applied to four pollen
records, covering the last glacial - interglacial
transition, to derive quantitative estimates of changes
in temperature and precipitation for the South American
mid-latitudes (41$/sp/circ$). Although there are
variations among the records, there is generally good
agreement, indicating largely consistent regional scale
change. Comparisons of the quantitative climate
reconstructions with qualitative records of
paleoenvironmental conditions in the region show good
agreement.
Data from the Lake District of Chile and Argentina were
then integrated with quantitative paleotemperature
records from the equatorial region of South America, and
with temperature estimates from the Byrd (Antarctica)
$/delta/sp[18]$O record. This paleoenvironmental data set
was compared to general circulation model (GCM) scenarios
of climate change. Three different sets of model output
from the GIST-NESS GCM for the LGM, each with different a
different set of sea surface temperature (SST) values
were compared. The model run using calculated values for
SST based on an ocean heat convergence (OHC) and ocean
heat transport (OHT) model reproduced the most accurate
surface temperature values for the equatorial and polar
regions. However, this model did not perform well in the
mid-latitudes $(30/sp/circ$-60$/sp/circ$S). Model output
from the NCAR community climate model (CCM1) for time
slices spanning from the LGM to 6000 years ago were then
compared to the paleoenvironmental data set. This
comparison shows that the model's linear response to
changing boundary conditions is not an accurate
reconstruction of the pattern of climate change that has
occurred since the LGM. The paleoenvironmental data show
that the onset of warming occurred first at the high and
mid-latitudes, preceding equatorial warming by as much as
7000 years. The paleoenvironmental data also show that
the continuous warming shown in the model output is
inaccurate. Warming occurred abruptly, and reversals are
recorded at all latitudes. In the polar region,
temperatures jumped 5$/sp/circ$C from 21 Ka to 16 Ka, and
had reached modern conditions by 14 Ka. At the mid-
latitudes, temperatures transitioned from the full
glacial minimum to warmer than today between 21 Ka and 16
Ka, while at the equator, temperatures did not start to
warm until ca. 14 Ka.
------------------------------------------------------------
Title: Role of atmosphere-ocean interaction in the midlatitude
North Atlantic on interannual climate variability
Pub No: 9611415
Author: Bhatt, Uma Suren
Degree: PhD
School: THE UNIVERSITY OF WISCONSIN - MADISON
Date: 1996
Pages: 174
Adviser: Houghton, David D.; Battisti, David S.
Source: DAI-B 57/01, p. 397, Jul 1996
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: The primary mode of observed interannual variability in
the North Atlantic is characterized by a north-south
oriented dipole pattern in anomalies of surface air
temperature and sea surface temperature (SST). The
atmospheric circulation associated with the dipole mode
of variability is consistent with the notion of the
atmosphere forcing the ocean. The impact of air-sea
interaction on the dipole-like mode of variability is
examined using a mixed layer model (MLM) of the upper
ocean in the North Atlantic between 20-60$/sp/circ$N
coupled to the NCAR Community Climate Model (CCM1). The
climatology of the MLM ocean temperature is adjusted to
be consistent with the SSTs that form the lower boundary
conditions for CCM1 by including heat flux corrections in
the net forcing of the ocean. Heat and salt flux
corrections are calculated in a series of uncoupled
simulations where the MLM is forced with CCM1 surface
fluxes.
The natural variability in a 31-year integration of the
MLM in the North Atlantic coupled to CCM1 is compared to
a CCM1 control simulation of similar length with SSTs
specified to have the same climatological annual cycle as
in the coupled integration. The mean December to February
(DJF) climatology is essentially unchanged with the
inclusion of midlatitude air-sea interaction. However,
air-sea interaction leads to significant increases in the
persistence of air temperature anomalies on interannual
as well as monthly time scales.
In the model subpolar North Atlantic, air and ocean
temperature anomalies are significantly autocorrelated
(0.4 to 0.6) from one winter to the following winter.
These autocorrelations are consistent with the 'Re-
emergence' mechanism (Namias and Born, 1970). Deep ocean
temperature anomalies, present at the end of one winter,
remained sequestered below the shallow summer mixed
layer. As the mixed layer deepens during the following
fall, ocean temperature anomalies from the previous
winter are reincorporated into the surface layer.
February mixed layer ocean temperatures are strongly
correlated with submixed layer ocean temperatures during
the following summer and surface ocean temperature
anomalies the following winter. An uncoupled sensitivity
experiment is performed, in which the MLM is forced with
heat, momentum, and freshwater fluxes from the coupled
simulation, and anomalies are supressed in mixed layer
depth and entrainment heating. The sensitivity experiment
finds that the autocorrelations from one winter to the
next in ocean temperature are weak when anomalies in
entrainment heating or mixed layer depths are supressed.
The 'Re-emergence' mechanism does not play an important
role in the subtropical model domain. Observed air and
ocean temperature autocorrelations from one winter to the
next are strong (weak) in the northern (southern) part of
the North Atlantic basin, in agreement with model
results.
Air temperature anomalies decay more slowly as a result
of air-sea interaction. Short-term autocorrelations of
air temperature are statistically significant up to 1-2
and 3-4 months in the control and coupled simulations,
respectively. When air temperatures are not affected by
SST anomalies as in the control simulation, the turbulent
heat fluxes act to strongly damp air temperature
anomalies (Frankignoul, 1985). With the inclusion of
variable ocean temperatures, the 'thermal damping' of
atmospheric temperature anomalies is weaker. Consistent
with these findings, the variance of air temperature
increases and of total heat flux decreases as a result of
coupling. (Abstract shortened by UMI.)
------------------------------------------------------------
Title: Global optimization of numerical models by simulated
annealing (Weather prediction)
Pub No: 9957125
Author: Campbell, William Francis
Degree: PhD
School: UNIVERSITY OF MARYLAND, COLLEGE PARK
Date: 1999
Pages: 212
Adviser: Baer, Ferdinand
ISBN: 0-599-60324-0
Source: DAI-B 60/12, p. 6156, Jun 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373)
Abstract: The problems of vertical level placement and three-
dimensional truncation of numerical models are
investigated. Because the atmosphere is inhomogeneous,
anisotropic, and unbounded above, there are no natural
basis functions in the vertical upon which to base
spectral methods for numerical prediction. A finite
difference formulation in the vertical, with levels
typically chosen to match observational levels, is used
by most forecast and climate models. Our method computes
the number of vertical levels as a function of horizontal
scaling, and selects their location as a function of
vertical coordinate system and atmospheric data.
The central premise of our research is that the optimal
grid for computation is the grid that yields the best
linear spline fit to the meteorological fields of
interest. A continuous “ground truth” for
each field was constructed from analyzed wind and
temperature data, via cubic splines. The best linear
spline fit was then found by minimizing the integral of
the squared difference between arbitrary linear splines
and ground truth, via simulated annealing. Using NCAR's
Community Climate Model (CCM3), grids produced with
seasonal mean data for summer and winter were tested
against each other and against the standard grid at the
same average resolution.
Allowing resolution to change dynamically between the
horizontal and the vertical enables the direct prediction
of the optimum truncation ratio. Because the energy of
the grid is affected only by the <italic>distribution
</italic> of curvature in each dimension, simulated
annealing, meteorological data, and the linear spline
hypothesis suffice to solve the level placement and
relative truncation problems with no additional
assumptions.
The applicability of this procedure is quite general:
given the characteristic structures of any set of PDE's,
the optimal predictive grid can be constructed. In
addition, a global optimization method that is heretofore
absent from the meteorological literature, but of general
utility, is employed. Most importantly, a specific,
testable prediction of truncation ratio is produced.
------------------------------------------------------------
Title: Climate variability in the North Atlantic on decadal and
multi-decadal time scales: A numerical study
Pub No: 3001162
Author: Cheng, Wei
Degree: PhD
School: UNIVERSITY OF MIAMI
Date: 2000
Pages: 154
Adviser: Bleck, Ranier; Rooth, Claes G. H.
ISBN: 0-493-09584-5
Source: DAI-B 62/01, p. 133, Jul 2001
Subject: PHYSICAL OCEANOGRAPHY (0415); PHYSICS, ATMOSPHERIC
SCIENCE (0608)
Abstract: The goal of this work is to understand the mechanisms
that drive the decadal and multi-decadal climate
variability in the North Atlantic. Natural climate
variability on these particular time scales occupies a
central position in discussions of anthropogenic climate
changes, but many aspects related, to this issue are
still poorly understood.
The major tool used in this study is a coupled general
circulation model consisting of the NCAR CCM3 and the
Miami Isopycnic Coordinate Ocean Model. The simulated
decadal variability in the North Atlantic is dominated by
a tri-pole pattern in sea surface temperature and a North
Atlantic Oscillation (NAO) pattern in sea level pressure.
The associated oceanic fluctuations are characterized by
a delayed subtropical gyre response to anomalou's NAO
surface wind stress forcing and advection of SST
anomalies originating near the western boundary into the
interior ocean. Separate ocean-alone experiments suggest
that the SST variability can not be attributed solely to
passive response of the ocean to atmospheric thermal
forcing.
It is also found that a quasi-oscillatory fluctuation of
the thermohaline circulation (THC) in the North Atlantic
ocean with an approximate time scale of 30 years is
present in the coupled but not in uncoupled simulations.
The latter were forced with either Newtonian relaxation
boundary conditions (based on a monthly climatology of
the atmospheric state variables such as the surface air
temperature and surface specific humidity) or with
imposed monthly varying heat and fresh water flux
conditions.
These results suggest that the variability of the THC in
this model is neither an ocean internal phenomenon nor a
passive response of the ocean to atmospheric forcing.
Rather, it is a coupled process involving both the ocean
and the atmosphere. The THC oscillation appears to be
driven by surface heat flux forcings while the effects of
surface fresh water fluxes are secondary. Two delay
effects are crucial for maintaining this oscillation. One
is the delay of the North Atlantic overturning strength
relative to the deep water formation rate in the deep
water production region; the other is the delay of the
associated SST and surface heat flux anomalies in the
sinking region relative to the overturning amplitude
itself.
The sea surface temperature signal associated with the
THC oscillation bears some resemblance to an SST
interdecadal pattern extracted from observational data
(Kushnir, 1993). Accompanying anomalies of northern
hemispheric surface air temperature have positive values
over the Pacific and Atlantic Oceans and negative values
over the Eurasian and North American continents. In
addition to anomalies in sea surface temperature and
surface air temperature, there are also variations in
atmospheric flow pattern over the North Atlantic, namely,
an anomalous northerly flow over the Labrador Sea when
the THC circulation is strong.
------------------------------------------------------------
Title: Modeling the direct and indirect climatic effects of
tropospheric sulfate aerosols
Pub No: 9967719
Author: Cox, Stephen J.
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT ALBANY
Date: 2000
Pages: 103
Adviser: Wang, Wei-Chyung
ISBN: 0-599-72439-0
Source: DAI-B 61/04, p. 1996, Oct 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); ENVIRONMENTAL
SCIENCES (0768)
Abstract: Modeling studies of the climatic effects of tropospheric
sulfate aerosols are presented. Both the direct
scattering by the aerosols and the indirect effect of
enhanced cloud albedo from increased aerosol numbers are
addressed, in separate studies. The direct effect study
uses aerosol mass concentrations from the MOGUNTIA
chemical transport model. A parameterization is developed
to model the radiative forcing due to direct shortwave
scattering by the aerosols in the NCAR Community Climate
Model, an atmospheric general circulation model. Aerosol
layer optical properties are folded into the direct and
diffuse surface albedo. The aerosol forcing is similar in
magnitude, but opposite in sign, to the longwave forcing
by anthropogenic greenhouse gases such as CO<sub>
2</sub>, CH<sub>4</sub>, N<sub>2</sub>O,
CF<sub>2</sub>CL<sub>2</sub>, and CFCL<sub>3</sub>. CCM1
is run for thirty-five years with equal and opposite
global annual mean aerosol and greenhouse forcings, and
the results compared to a control run with no forcing. It
is determined that the global mean temperate responds to
the forcings equally, with a global sensitivity of 1.25
K/(W m<super> −2</super>), but the regional
temperature response shows marked variation, which could
not be predicted simply from the forcing pattern. The
aerosol forcing is concentrated in the industrial
continental areas of the Northern Hemisphere
midlatitudes, yet a strong cooling response is noted in
regions thousands of kilometers away (for instance,
western Canada) from centers of aerosol concentration.
The indirect effect is studied with more recent sulfate
estimates, from the Oslo Chemical Transport Model. Field
studies are used to relate sulfate mass concentration to
cloud droplet number concentration, and subsequently to
cloud droplet effective radius. The indirect
parameterization is incorporated into NCAR CCM3, along
with a new shortwave parameterization which allows the
full vertical distribution of the aerosols to be
accounted for. The indirect radiative forcing is found to
be a cooling of 0.47 W m<super>−2</super>, smaller
than the direct forcing of 1.15 W
m<super>−2</super>, though still significant. The
direct forcing is strongest over the Northern Hemisphere
land, whereas the indirect forcing occurs more strongly
over the Northern Hemisphere ocean, likely due to greater
susceptibility of the more pristine marine air to
condensation nuclei enhancement.
------------------------------------------------------------
Title: Longwave radiative transfer in the atmosphere: Model
development and applications
Pub No: 3092290
Author: Delamere, Jennifer Simmons
Degree: PhD
School: UNIVERSITY OF ALASKA FAIRBANKS
Date: 2003
Pages: 153
Adviser: Stamnes, Knut H.
ISBN: 0-496-39997-9
Source: DAI-B 64/05, p. 2231, Nov 2003
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373)
Abstract: A FLexible Radiative Transfer Tool (FLRTT) has been
developed to facilitate the construction of longwave,
correlated <italic>k</italic>-distribution, radiative
transfer models. The correlated <italic>k</italic>-
distribution method is a technique which accelerates
calculations of radiances, fluxes, and cooling rates in
inhomogeneous atmospheres; therefore, correlated <italic>
k</italic>-distribution models are appropriate for
simulations of satellite radiances and inclusion into
general circulation models. FLRTT was used to build two
new rapid radiative transfer models, RRTM_HIRS and
RRTM_v3.0, which maintain accuracy comparable to the
line-by-line radiative transfer model LBLRTM.
<italic>Iacono et al</italic>. [2003] evaluated upper
tropospheric water vapor (UTWV) simulated by the National
Center for Atmospheric Research Community Climate Model,
CCM3, by comparing modeled, clear-sky brightness-
temperatures to those observed from space by the High-
resolution Radiation Sounder (HIRS). CCM3 was modified to
utilize the rapid radiative transfer model RRTM and the
separate satellite-radiance module, RRTM_HIRS, which
calculates brightness temperatures in two HIRS channels.
By incorporating these accurate radiative transfer models
into CCM3, the longwave radiative transfer calculations
have been removed as a significant source of error in the
simulations. An important result of this study is that
CCM3 exhibits moist and dry discrepancies in UTWV of 50%
in particular climatic regions, which may be attributed
to errors in the CCM3 dynamical schemes.
RRTM_v3.0, an update of RRTM, is a rapid longwave
radiative transfer appropriate for use in general
circulation models. Fluxes calculated by RRTM_v3.0 agree
with those computed by the LBLRTM to within 1.0
W/m<super>2</super> at all levels, and the computed
cooling rates agree to within 0.1 K/day and 0.3 K/day in
the troposphere and stratosphere, respectively.
This thesis also assessed and improved the modeling of
clear-sky, longwave radiative fluxes at the Atmospheric
Radiation Measurement Program North Slope of Alaska site
by simultaneously addressing the specification of the
atmosphere, radiometric measurements, and radiative
transfer modeling. Consistent with findings from other
field sites, the specification of the atmospheric water
vapor is found to be a large source of uncertainty in
modeled radiances and fluxes. Improvements in the
specification of carbon dioxide optical depths within
LBLRTM resulted, in part, from this analysis.
------------------------------------------------------------
Title: Speciated local aerosol characteristics and radiative
forcing at a rural midwestern site
Pub No: 9971067
Author: Dillner, Ann Marie
Degree: PhD
School: UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN
Date: 2000
Pages: 162
Adviser: Larson, Susan M.
ISBN: 0-599-76207-1
Source: DAI-B 61/05, p. 2697, Nov 2000
Subject: ENGINEERING, ENVIRONMENTAL (0775); PHYSICS, ATMOSPHERIC
SCIENCE (0608)
Abstract: In this research, physical and chemical properties of
ambient aerosols were measured at a rural perturbed mid-
latitude site (Bondville, IL) and used to calculate the
aerosol optical properties and the resulting direct
radiative forcing. Size-segregated aerosol samples were
collected during the summer of 1997 using three parallel
MOUDIs operating at ambient relative humidity. Two sample
sets were used to obtain sulfate, organic carbon (OC),
elemental carbon (EC), carbonate and total aerosol mass.
The third sample set was used to obtain the size-specific
and wavelength-dependent extinction efficiency of EC.
The measured submicrometer mass concentration was 11.4
± 4.0 μg m<super>−3</super>. Ammonium
sulfate comprised nearly half of the submicrometer
aerosol and OC plus EC comprised 25%.
Water content for ammonium sulfate and OC was estimated
using both Köhler theory and parameterized water
uptake curves from the literature. Water content for
internally mixed aerosols was determined using a ZSR
method. Aerosol optical properties (extinction
efficiency, asymmetry parameter, single scatter albedo)
were calculated from measured size distributions and
wavelength dependent refractive indexes for each species
and for internal and external mixtures using Mie theory.
A technique, utilizing transmission measurements through
extracts of size segregated ambient aerosol samples, was
developed to obtain the extinction efficiency of EC.
Measured EC extinction efficiencies ranged from 7.3 to
1.7 m<super>2</super> g<super>−1</super> at 550 nm,
depending on particle diameter. Normalized direct aerosol
radiative forcing (W g<super>−1 </super>) was
calculated using the Column Radiation Module (CRM) of the
National Center for Atmospheric Research (NCAR) Community
Climate Model (CCM3). Aerosol optical properties, used in
the model, were assumed to be uniform throughout the
lowest one kilometer of the atmosphere. The normalized
forcing due to ammonium sulfate was −340 ±
10 W g<super>−1</super>. OC was 1/3 larger and
residue was 1/3 smaller. EC within an internally mixed
aerosol was shown to suppress forcing.
This research supports the view that species other than
ammonium sulfate, namely EC, OC and dust-like aerosol,
have significant radiative effects. Although the mass
percentage of EC may be low at rural sites, ignoring the
presence of EC aerosol leads to an over estimation of the
aerosol forcing.
------------------------------------------------------------
Title: Short-range ensemble forecasting of an explosive
cyclogenesis with a limited-area model
Pub No: 9626568
Author: Du, Jun
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 1996
Pages: 146
Adviser: Mullen, Steven L.; Sanders, Frederick
Source: DAI-B 57/04, p. 2623, Oct 1996
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); HYDROLOGY (0388)
Abstract: Since the atmosphere is a chaotic system, small errors in
the initial condition of any numerical weather prediction
(NWP) model amplify as the forecast evolves. To estimate
and possibly reduce the uncertainty of NWP associated
with initial-condition uncertainty (ICU), ensemble
forecasting has been proposed which is a method of,
differently from the traditional deterministic
forecasting, running several model forecasts starting
from slightly different; initial states.
In this dissertation, the impact of ICU and short-range
ensemble forecasting (SREF) on quantitative precipitation
forecasts (QPFs), as well as on sea-level cyclone
position and central pressure, is examined for a case of
explosive cyclogenesis that occurred over the contiguous
United States. A limited-area model (the PSU/NCAR NM4) is
run at 80-km horizontal resolution and 15 layers to
produce a 25-member, 36-h forecast ensemble. Lateral
boundary conditions for the MM4 model are provided by
ensemble forecasts from a global spectral model (the NCAR
CCM1). The initial perturbations of the ensemble members
possess a magnitude and spatial decomposition which
closely match estimates of global analysis error, but
they were not dynamically-conditioned. Results for 80-km
ensemble forecast are compared to forecasts from the then
operational Nested Grid Model (NGM), a single 40-km MM4
forecast, and a second 25-member MM4 ensemble based on a
different cumulus parameterization and slightly different
initial conditions.
Acute sensitivity to ICU marks ensemble QPF and the
forecasts of cyclone position and central pressure.
Ensemble averaging always reduces the rms error for QPF.
Nearly 90% of the improvement is obtainable using
ensemble sizes as small as 8-10. However, ensemble
averaging can adversely affect the forecasts related to
precipitation areal coverage because of its smoothing
nature. Probabilistic forecasts for five mutually
exclusive, completely exhaustive categories are found to
be skillful relative to a climatological forecast.
Ensemble sizes of $/sim$10 can account for 90% of
improvement in probability density function.
Our results indicate that SREF techniques can now provide
useful QPF guidance and increase the accuracy of
precipitation, cyclone position, and cyclone's central
pressure forecasts. With current analysis/forecast
systems, the benefit from simple ensemble averaging is
comparable to or exceed that obtainable from improvement
in the analysis/forecast system.
------------------------------------------------------------
Title: Regional simulation of North American interannual climate
variability
Pub No: 9998321
Author: Dutton, Jan Frederik
Degree: PhD
School: THE PENNSYLVANIA STATE UNIVERSITY
Date: 2000
Pages: 134
Adviser: Barron, Eric
ISBN: 0-493-06588-1
Source: DAI-B 61/12, p. 6518, Jun 2001
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); APPLIED MECHANICS
(0346)
Abstract: The interannual variability of the RegCM2 regional
climate model, with a U.S. centered domain, forced by the
NCAR CCM3 global climate is the main focus of this study.
A 6 member 10 year CCM3 ensemble, from January 1, 1968 to
December 31, 1978, forced globally by reconstructed
observed sea surface temperatures, provides RegCM2
boundary conditions.
An understanding of how RegCM2 responds to CCM3
interannual variability is developed using an anomaly
pattern correlation (APC) analysis of the CCM3 and RegCM2
monthly averaged 500 mb heights, surface temperature, and
precipitation. All three variables show a distinct APC
annual cycle.
The effect of regional climate modeling on simulated
climate reproducibility compared using the modeled
ensemble run variances. In certain regions RegCM2 surface
temperature normalized ensemble run variance is
significantly lower than CCM3, suggesting higher
reproducibility in these regions. RegCM2 precipitation
reproducibility is found to be lower than CCM3 in all
regions, indicating higher resolution simulations have
lower reproducibility.
A empirical orthogonal function (EOF) analysis of the
dominant precipitation and surface temperature modes of
variability is also presented. The EOF analyses use 60
years (6 ensemble members x 10 years) of RegCM2, CCM3,
and a gridded observed data. RegCM2 does not
significantly alter the primary modes of CCM3 surface
temperature variability. Furthermore, the observed
primary modes of surface temperature variability are
similar to those modeled. Neither model captures the
primary mode of winter precipitation variability. The
modeled primary mode of precipitation variability,
focused on the west U.S. coast, is similar to the
observed second mode. The RegCM2 increases the amplitude
of the CCM3 mode, improving the simulation of winter
precipitation variability relative to the observations.
The analysis of summer surface temperature and
precipitation variability reveals that regional scale
forcing, such as the low-level jet, plays an important
role in modifying the locations of the primary modes of
variability. The RegCM2 significantly improves the jet
simulation, shifting the precipitation variability to
midwestern and eastern U.S. Despite these changes, the
results show the CCM3 interannual variability signal is
present in the RegCM2 signal throughout the year.
------------------------------------------------------------
Title: Tropical climate stability, Hadley circulation, and deep
cumulus convection: Vital synergism on a wet planet
Pub No: 9975794
Author: Fleischfresser, Luciano
Degree: PhD
School: THE UNIVERSITY OF OKLAHOMA
Date: 2000
Pages: 129
Adviser: Fiedler, Brian
ISBN: 0-599-81465-9
Source: DAI-B 61/06, p. 3095, Dec 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); ENVIRONMENTAL
SCIENCES (0768); APPLIED MECHANICS (0346)
Abstract: This research is about developing a more internally
consistent formulation of cumulus convection and the
atmospheric branch of the hydrological cycle in a newly
developed Hadley circulation model. The ultimate goal is
to analyze the climate equilibrium of a symmetric
tropical hydrostatic atmosphere, particularly studying
cause and effect relations determining the magnitude of
water vapor-related feedbacks in climate sensitivity
experiments.
Important features of the proposed formulation for
precipitating deep turbulent clouds include the ability
to calculate precipitation efficiencies, a new
postulation relating cumulus buoyancy to solar radiation,
and the implicit account of latent heat release that
manifest itself by scaling cumulus drafts to observed
magnitudes. The Hadley model is based on primitive
equations, and it incorporates the NCAR column radiation
scheme as well as the atmospheric branch of the
hydrological cycle. To calculate climatic feedbacks, the
inverse simulation approach is used. An interrelationship
technique is applied to diagnose feedback factors
associated with changes of water vapor amount and
distribution, of lapse-rate, and of deep cumulus cloud
cover. The aim is to contrast the novel model for deep
clouds with a mass flux deep cumulus parameterization
when a thermally direct circulation (Hadley cell) is
present.
When only a lapse-rate adjustment is used to crudely
represent tropical convection, the calculated climate
sensitivity lies in the typical range of equatorial
sensitivities given by global circulation models (GGMs).
This result suggests that the Hadley model is capturing
the essential physics of these models as far as these
sensitivities are concerned. In the comparison analyses,
the climate equilibrium is stable and effected by net
positive feedback when the new cumulus model is used.
Moreover, the calculated tropical climate sensitivities
are consistently lower than the aforementioned typical
range, bringing them closer to sensitivities suggested by
observed data. Interestingly, the tropical climate
equilibrium is unstable with the mass flux scheme. It is
shown quantitatively that relative humidity changes in
the model upper-troposphere determine the sign of the
water vapor feedback. Recommendations to narrow humidity
uncertainties in climate change simulations are
presented.
------------------------------------------------------------
Title: The development of a three-dimensional general
circulation model with coupled chemistry
Pub No: 9805287
Author: Gross, Gerhard Wayne
Degree: PhD
School: PORTLAND STATE UNIVERSITY
Date: 1997
Pages: 382
Adviser: Khalil, M. Aslam K.
ISBN: 0-591-55236-1
Source: DAI-B 58/08, p. 4282, Feb 1998
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: A coupled climate-chemistry model for the troposphere and
lower stratosphere has been developed that includes on-
line local actinic flux calculation. The coupling of
chemistry with a climate model and the internal
calculation of actinic flux allows the model to simulate
a variety of interactions and feedbacks between
atmospheric processes that are ordinarily excluded from
general circulation models.
The climate model is an altered version of the CCM3
(Community Climate Model Version 3) from NCAR (National
Center for Atmospheric Research). The spectral resolution
of the radiation code of the model has been increased 8-
fold in the region 200-700 nm, with highest resolution
between 245-350 nm. Actinic flux is calculated by the
radiation code for each spectral interval and each model
grid cell at a user defined frequency set to 1 hour in
this work. The coupled tropospheric chemistry component
uses climatological data from the climate model including
temperature, pressure, water vapor concentration, actinic
flux, and atmospheric transport.
The OH distributions generated by a 3 year simulation of
the coupled model in the partially coupled mode show a
zonal maximum over the tropics as expected. Seasonal
variations displace the zonal maximum towards the summer
pole by about 5$/sp/circ$ in the southern hemisphere and
about 15$/sp/circ$ in the northern hemisphere. The
distributions show somewhat more structure compared to
results from other model studies. During the solstice
months the OH concentration is greatest at the surface
and during the equinox months the maximum is slightly
elevated to approximately 1.5 km. The concentration of
the equatorial maximum decreases with altitude and then
increases above about 400 mb (7 km).
The model calculated, global, tropospheric, average is
1.1 $molecules/cm/sp3$ and is slightly higher than
results from other studies. The global average at the
surface is 1.2 $molecules/cm/sp3$ and agrees with
measurements and model studies. The globally averaged
amount of $CH/sb4$ destroyed by oxidation with OH is
calculated to be 461 $Tg/yr$ and also agrees with
independent estimates from other researchers. The
distribution of formaldehyde is consistent with
measurements made by other groups.
------------------------------------------------------------
Title: I. Variability of the outgoing thermal IR spectra and its
application in GCM validation. II. The detection of
cloud/aerosol in the outgoing thermal IR spectra
Pub No: 3151366
Author: Huang, Xianglei
Degree: PhD
School: CALIFORNIA INSTITUTE OF TECHNOLOGY
Date: 2004
Pages: 182
Adviser: Yung, Yuk L.
ISBN: 0-496-11390-9
Source: DAI-B 65/10, p. 5193, Apr 2005
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); PHYSICS, ASTRONOMY
AND ASTROPHYSICS (0606)
Abstract: The theme of this thesis is studying the outgoing
infrared spectra of Earth and Mars. In Chapter 1, the
importance and the feasibility of using the outgoing
thermal IR spectra in testing model's variability are
discussed. Chapter 2 investigates the temporal
variability over the tropical and midlatitude Pacific
seen from Infrared Interferometer Spectrometer (IRIS)
observations and corresponding synthetic spectra based on
simulations from two general circulation models (GCMs),
UCLA GCM and NCAR CAM2. The discrepancies between modeled
and observed variability are substantial. Further
examination shows that these discrepancies are most
likely due to deficiencies in simulating the seasonal and
intraseasonal variations of the Walker Circulation in the
tropical Pacific and the seasonal variations of low
cloud, boundary-layer temperature, and stratospheric
temperature in the midlatitude Pacific. Chapter 3
presents a survey of the spatial variability seen from
Atmospheric Infrared Sounder (AIRS) spectra and
corresponding synthetic spectra based on NCAR CAM2
simulation. To a large extent, the simulated variability
agrees well with the observed counterpart. The major
discrepancies can be attributed to the incorrect location
of ITCZ in the western Pacific, the underrepresented dust
aerosol over the Arabian Sea and off the Atlantic Coast
of North Africa, and the overestimated spatial variation
of stratospheric temperature in the model. Chapter 4
presents a comparative study of the variability seen in
the Martian outgoing infrared spectra collected by MGS-
TES (Thermal Emission Spectrometer). The negative
correlation between dust and water ice spectral features
seen in this analysis suggests that, to some extent, dust
and water ice cloud are mutually exclusive of each other
in the Martian atmosphere. Chapter 5 presents a
sensitivity study of identifying optically thin cirrus
from high-resolution infrared spectra based on the line
shapes in the residual spectra. This cirrus-detection
approach is original in the sense of making use of
information content contained in such measurements.
Chapter 6 presents a tri-spectral algorithm to detect
water ice cloud, dust, and surface anisothermality from
low-resolution Martian outgoing thermal IR spectra. This
algorithm can be used to screen large amounts of data to
get a quick overview.
------------------------------------------------------------
Title: Adaptive grids in weather and climate modeling
Pub No: 3121951
Author: Jablonowski, Christiane
Degree: PhD
School: UNIVERSITY OF MICHIGAN
Date: 2004
Pages: 266
Adviser: Penner, Joyce E.
ISBN: 0-496-69302-7
Source: DAI-B 65/02, p. 792, Aug 2004
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: Adaptive Mesh Refinement (AMR) provides an attractive
framework for atmospheric flows since it allows improved
horizontal resolution in a limited region without
requiring a fine grid resolution throughout the entire
model domain. In this thesis, the adaptive grid technique
has been applied to a revised version of NCAR/NASA's next
generation dynamical core for climate and weather
research. This hydrostatic so-called Lin-Rood dynamics
package with a conservative finite volume discretization
in flux form provides highly efficient algorithms for
high performance computing.
The adaptive model design utilizes a spherical adaptive-
grid library which is based on a cache-efficient block-
structured data layout. This AMR communication library
for parallel processors has been newly developed in the
Computer Science Department at the University of
Michigan. All blocks are self-similar and split into four
in the event of refinement requests. The resolution of
neighboring blocks can only differ by a factor of two
which leads to cascading refinement regions.
The adaptive dynamical core is run in two configurations:
the full 3D hydrostatic dynamical core on the sphere and
the corresponding 2D shallow water model that has been
extracted out of the 3D version. This shallow water setup
serves as an ideal testbed for the horizontal
discretization and the 2D adaptive-mesh strategy. It
further allows the efficient testing of interpolation
routines at fine-coarse grid interfaces.
The static and dynamic adaptations are tested using the
standard shallow water test suite and a newly-developed
idealized 3D baroclinic wave test case. Static
adaptations are used to vary the resolution in pre-
defined regions of interest. This includes static
refinements near mountain ranges or static coarsenings in
the longitudinal direction for the implementation of a
so-called reduced grid in polar regions. Dynamic
adaptations are based on flow characteristics and guided
by refinement criteria that detect user-defined features
of interest during a simulation. In particular, flow-
based refinement criteria, such as vorticity or gradient
indicators, are suggested. Refinements and coarsenings
occur according to pre-defined threshold values.
This research project is characterized by an
interdisciplinary approach involving atmospheric science,
computer science and applied mathematics.
------------------------------------------------------------
Title: A physically-based snow model coupled to a general
circulation model for hydro-climatological studies
Pub No: 3050315
Author: Jin, Jiming
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 2002
Pages: 162
Adviser: Sorooshian, Soroosh
ISBN: 0-493-64911-5
Source: DAI-B 63/04, p. 1761, Oct 2002
Subject: HYDROLOGY (0388); PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: A Snow-Atmosphere-Soil Transfer (SAST) model has been
developed to extend the point snowmelt model to vegetated
areas using the parameterization concepts of the
Biosphere-Atmosphere Transfer Scheme (Dickinson et al.
1993). The model applications for short-grass and forest
fields show that the simulated surface temperature,
albedo, and snow depth have close agreement with
observations. In addition, because of biases in simulated
runoff in the high-latitudes, a Shuffled Complex
Evolution (Sorooshian et al. 1993) scheme for automatic
calibration has been connected with the SAST model to
determine the realistic distribution of runoff components
from different soil layers and search the optimized
parameter set. The calibrated runoff closely matches
observations.
Because the Community Climate Model version 3 (CCM3)
coupled with the SAST model overestimates snow depth and
precipitation and underestimates surface temperature over
the Rocky Mountains, remotely sensed snow depth data have
been assimilated in the model to alleviate model
discrepancies based on energy and mass balances. The
improved surface temperature simulations result from the
decreased snowmelt and albedo in winter and spring and
from the weakened evaporation in summer due to drier
soil. Meanwhile, modeled summer precipitation over the
Rocky Mountains has a minor improvement.
The relationship between the variations of tropical
Pacific SST and snowpack anomalies in the western United
States (U.S.) has been studied by comparing observations
and CCM3 output. The results indicate that in the
northwestern U.S., the warm tropical Pacific phase of the
El Niño-Southern Oscillation (ENSO) is associated
with diminished snowpack while its cool phase is related
to enhanced snowpack. This relationship is largely
determined by winter precipitation variability for the
observations; however, it relies heavily on the
variations of temperature due to the biases in
atmospheric patterns for the model output. In the
southwestern U.S., positive snowpack anomalies for both
observations and simulations result from the strong warm
phase of the ENSO and negative ones are connected with
exaggerated local precipitation in fall.
------------------------------------------------------------
Title: Interpolation of surface radiative temperature measured
from polar orbiting satellites to a diurnal cycle
Pub No: 9923351
Author: Jin, Menglin
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 1999
Pages: 152
Adviser: Dickinson, Robert E.
ISBN: 0-599-22782-6
Source: DAI-B 60/03, p. 1128, Sep 1999
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); REMOTE SENSING
(0799); ENVIRONMENTAL SCIENCES (0768)
Abstract: The land surface skin temperature diurnal cycle (LSTD) is
very important for the understanding of surface climate
and for evaluating climate models. This variable,
however, cannot be obtained globally from polar-orbiting
satellites because the satellites usually pass a given
area twice per day and because their infrared channels
cannot observe the surface when the sky is cloudy.
In order to more optimally use the satellite data, this
research is designed, for the first time, to solve the
above two problems by advance use of remote sensing
techniques and climate modeling. Specifically, this work
is divided into two parts. Part one deals with obtaining
the skin temperature diurnal cycle for cloud-free cases.
We have developed a “cloud-free algorithm” to
combine model results with satellite and surface-based
observations, thus interpolating satellite twice-daily
observations to the diurnal cycle. Part two studies the
cloudy cases. The “cloudy-pixel treatment”
presented here is a hybrid technique of
“neighboring-pixel” and “surface air
temperature” approaches. The whole algorithm has
been tested against field experiments and climate model
CCM3/BATS in global and single column mode simulations.
It shows that this proposed algorithm can obtain skin
temperature diurnal cycles with an accuracy of 1–2
K at the monthly pixel level.
------------------------------------------------------------
Title: The onset of convection in the Madden-Julian oscillation
Pub No: 9948702
Author: Kemball-Cook, Susan Rives
Degree: PhD
School: UNIVERSITY OF CALIFORNIA, DAVIS
Date: 1999
Pages: 109
Adviser: Weare, Bryan
ISBN: 0-599-51118-4
Source: DAI-B 60/10, p. 5117, Apr 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: An observational study of the onset of convection in the
Madden-Julian Oscillation (MJO) was performed. Composites
of radiosonde data from the Comprehensive Aerological
Reference Data Set were constructed for an ensemble of
tropical stations in the Indian Ocean, Maritime
Continent, and western Pacific Ocean. Outgoing longwave
radiation from NOAA polar orbiting satellites was used as
a proxy for deep convection associated with the MJO, and
NCEP-NCAR Reanalysis data was used to diagnose low-level
convergence.
The composites suggest that for the off-equatorial
stations used in this study, the MJO period may be set by
the buildup and discharge of the low-level moist static
energy (h). This result supports the discharge-recharge
hypothesis of Blade and Hartmann (1993). MJO events are
most likely to occur when the off-equatorial atmosphere
has been destabilized through a combination of low level
h buildup and concurrent drying of the middle troposphere
by subsidence in the wake of the previous cycle of MJO
convection. The low-level h buildup is controlled by a
corresponding increase in low-level moisture. Following
an episode of MJO convection, a period of approximately
35 days is required to increase the low-level moisture to
the point where the atmosphere again becomes unstable to
deep convection. The convective event lasts about 20 days
and stabilizes the atmosphere by drying and cooling the
boundary layer and moistening and heating the middle and
upper troposphere. By drying and cooling the boundary
layer, convection discharges the low level h.
The increase in low-level moisture is not caused by the
1000 mb convergence, as suggested by frictional wave-CISK
theories. For the stations examined here, the convergence
lags the moist static energy buildup, and is instead in
phase with the convection. A possible mechanism for the
relatively slow moisture buildup lasting approximately 35
days is competition between surface fluxes of moisture
and the drying effect of entrainment of low h air into
the boundary layer. Evidence is found for the
preconditioning of the atmosphere to deep convection
through upward transport of moisture by shallow
convection.
------------------------------------------------------------
Title: Tropical dynamics near the stratopause: The two-day wave
and its relatives
Pub No: 9836209
Author: Limpasuvan, Varavut
Degree: PhD
School: UNIVERSITY OF WASHINGTON
Date: 1998
Pages: 209
Adviser: Leovy, Conway B.
ISBN: 0-591-89715-6
Source: DAI-B 59/06, p. 2808, Dec 1998
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); ENVIRONMENTAL
SCIENCES (0768)
Abstract: The two-day wave is observed in the Upper Atmosphere
Research Satellite (UARS) Microwave Limb Sounder (MLS)
temperature and water vapor data. During a 3-year period
(Dec. 1991-Sep. 1994), the wave signature is prominent
semiannually after each solstice and is comprised of a
zonal wavenumber 3 component with $[/sim]2.0$-day period
and a wavenumber 4 component with $[/sim]1.8$-day period.
Intra-annually, the wavenumber 3 amplitude during the
austral summer is nearly twice as strong as during the
boreal summer. The wavenumber 4 component however can be
equally strong in both summers. The wave-number 3 signal
tends to be dominant during the austral summer while the
wave 4 component is dominant during the boreal summer.
The derived zonal wind structure suggests that the
Charney-Stern inflection instability mechanism is
responsible for generating the two-day wave whose
amplitude resides mainly on the equatorward flank of the
summer easterly jet.
In some seasons, momentum redistribution by inertial
instability appears to destabilize the easterly jet from
which the barotropically unstable two-day wave grows. In
these instances, an independent study using the UARS
Cryogenic Limb Array Etalon Spectrometer (CLAES)
temperature (Hayashi et al., 1998) coincidently
identifies 'pancake' structures associated with inertial
instability. A possible connection between inertial
instability and the two-day wave has been discussed by
Hitchman (1985) and Orsolini et al. (1997).
The National Center for Atmospheric Research (NCAR)
Community Climate Model version 2 (CCM2) mechanistic
model is used to simulate this connection. Model
experiments show that, for a prescribed initial wind
condition with strong horizontal wind shear in the
tropics, inertial instability can trigger the two-day
wave. An increase in easterly wind curvature fostered by
inertial instability circulation destabilizes the jet in
low summer latitudes and allows first the growth of the
wavenumber 4 then the wavenumber 3 component of the two-
day wave. Near the stratopause, the two-day wave energy
propagation is directed equatorward away from the wave's
critical line source and westerly momentum is fluxed into
the easterly jet core by the wave. While much of the
wavenumber 4 activity is confined near the stratopause,
the wavenumber 3 energy can propagate upward well into
the mesosphere where strong Rayleigh damping is imposed.
The simulated waves' spatial and spectral characteristics
are fairly realistic.
------------------------------------------------------------
Title: On the relationship between tropical convection and clear
sky upper troposphere moisture
Pub No: 3088067
Author: Lin, Wuyin
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT STONY BROOK
Date: 2002
Pages: 103
Adviser: Zhang, Minghua
ISBN: 0-496-35829-7
Source: DAI-B 64/04, p. 1770, Oct 2003
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373)
Abstract: Upper troposphere water vapor is a crucial factor in the
climate system. The moisture abundance in the clear sky
upper troposphere is strongly influenced by tropical deep
convection. TOVS upper troposphere water vapor
measurements and ISCCP deep convective clouds are used to
investigate the relationship between upper troposphere
humidity (UTH) and frequency and area coverage of
tropical deep convection. The study shows that a more
diffused distribution of convection in the tropics is
associated with a higher UTH in the free troposphere,
while a more concentrated convection distribution is
associated with a drier free upper troposphere. It is
also shown that increased convective area coverage is
accompanied with an increased area coverage of less
frequent convection and a decreased area coverage of
highly frequent convection, and vice versa. The
identification of the geographical distribution of
convection perturbation associated with a potential
climate change is therefore important to the upper
troposphere water vapor feedback.
The mechanism behind the observed relationship is
interpreted using trajectory analysis. The results show
that a more diffused distribution of convection gives
rise to a shorter average horizontal distance and a less
vertical displacement between convection and clear
regions, and hence a moister clear sky condition.
Similarly, when deep convection is more concentrated, the
average traveling distance is longer, and the clear sky
upper troposphere is drier.
This process is verified using a simple heating driven
circulation model with prescribed distributions of
convective latent heating. The NCAR CCM is then used to
examine the relationship between UTH and convection. The
model is found to capture the relationship between water
vapor concentration and total convective area reasonably,
but it fails to reproduce the respective contributions
from highly and less frequent convections. The deficiency
lies in the fact that convection frequency is broadly
overestimated in the model. The area coverages of
different convective regimes are not simulated correctly.
The increase of total spatial coverage of deep convection
in the model is mainly reflected in the increased area
coverage of highly frequent convection, leading to an
opposite relationship between UTH and highly frequent
convection compared with the observations.
------------------------------------------------------------
Title: Improvement in runoff parameterization for global climate
mo