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2006 Seminars at COLA
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Title: Estimating and Correcting Global Weather Model Error
Speaker: Chris Danforth
Affiliation: Applied Mathematics and Scientific Computation Program, University of Maryland.
Date: January 9, 2006 at 11:00 a.m.
Abstract: With recent progress in data assimilation, the accuracy in the
initial conditions of numerical weather forecasts has been
substantially improved. As a result, accounting for systematic
errors associated with model deficiencies has become even more
important to ensemble prediction and data assimilation applications.
Leith (1978) proposed a statistical method to account for model bias
and systematic errors linearly dependent on the flow anomalies.
However, Leith's method is computationally prohibitive for high-
resolution operational models. This talk will discuss whether other
statistical correction approaches are feasible and effective for
possible operational use and compare the impact of correcting the
model integration with statistical corrections performed a posteriori.
Title: Hurricanes in a warming world: From genesis to revelation
Speaker: Prof. Peter J. Webster
Affiliation: School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA
Date: January 13, 2006 at 3:30 p.m.
Title: Understanding the Sahel drought using the GFDL models
Speaker: Dr. Jian Lu
Affiliation: GFDL, Princeton, NJ
Date: January 17, 2006 2:00 p.m.
Abstract: Both observational and modeling studies demonstrate the role of global
SSTs in orchestrating summer Sahel rainfall. Numerical experiments with
AM2, an AGCM recently developed at GFDL, driven by the observed record of
SST and sea ice from 1950 to 2000, successfully reproduce the observed
interdecadal variability of Sahelian rainfall. Further model experiments
are devised to examine the sensitivity of the summer Sahel rainfall to the
SST forcing from different ocean basins and to probe the mechanisms of how
the Sahelian climate responds to the tropical ocean warmth. In addition,
simulations of the 20th century with CM2 (an atmosphere-ocean coupled
model using AM2 and MOM4) are also analyzed. These coupled simulations
capture the late 20th century Sahel drought, but with reduced amplitude.
The simulated drought by CM2 can largely be attributed to anthropogenic
forcing. By fitting the SSTs indices to the Sahel rainfall through a
multiple regression model, we can quantify the contribution of SST to
Sahel rainfall in the 20th century. It is found in both the observations
and the 20th century simulations that a substantial amount of the variance
(~80%) of low-frequency Sahel rainfall can be accounted for by two SST
modes; one is related to a tropical SST warming trend on a global scale,
the other is an interhemispheric dipole over the Atlantic.
Based on this study, it is arguable that the greenhouse gas induced global
warming will exacerbate the likelihood that the late 20th century Sahel
drought will recur in future centuries.
Title: Interannual Ocean Variations
Speaker: Jianke Li
Affiliation: School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA
Date: January 23, 2006 11:00 a.m.
Abstract: TOPEX/Poseidon and Jason-1 altimeter data, coastal station data and hydrographic data are used to study the interannual ocean variations in several regions. 1. Along Australia’s western and southern coasts there exists strong interannual oscillation associated with El Niño/ La Niña winds in the equatorial Pacific Ocean. Analysis shows that both coastline direction and Leeuwin current affect the interannual variations through their own contributions. 2. Interannual oscillation also exists along the northern coast of the Gulf of Mexico due to wind stress curl in the North Atlantic Ocean. The along coast variations associated with this oscillation depend on the coastline direction, Loop Current mean shelf edge flow and the along shore wind. 3. Observations show that in the South Pacific most of the interannual sea level variability in the region 5 o S – 28 o S is west of 160 o W. Calculations show that this variability can be described by the first and second baroclinic vertical mode Rossby waves forced by the wind stress curl. East of 160 o W is a large ‘quite’ region of low interannual sea level variability, especially south of 5 o S. The large low variability region results because coastal sea level amplitude falls quickly southward so that the Rossby wave source is weak. The amplitude fall means, by geostrophy, that there is an onshore/offshore flow which feeds an El Niño current estimated to be 30 - 50 km wide with amplitude up to 20cm/sec.
Title: Observed Relationships between the El-Niño/ Southern Oscillation and the Extratropical Zonal-Mean Circulation
Speaker: Michelle L'Heureux
Affiliation: NOAA/NWS/NCEP/Climate Prediction Center, Camp Spring
Date: January 25, 2006 11:00 a.m.
Abstract: There is increasing evidence indicating that the climate response to variations in the El Niño- Southern Oscillation (ENSO) includes not only thermally forced zonal wind anomalies in the subtropics but also eddy-driven zonal wind anomalies that extend into the mid-to-high latitudes of both hemispheres. In this study, we provide new insights into the observed seasonally varying signature of ENSO in the extratropical zonal-mean circulation and examine the associated linkages with the dominant patterns of extratropical variability.
The zonal-mean extratropical atmospheric response to ENSO is characterized by two principal features: an equivalent barotropic dipole in the Southern Hemisphere (SH) zonal-mean zonal flow with centers of action located near ~40 and ~60 degrees during austral summer, and a weaker, but analogous, dipole in the Northern Hemisphere (NH) with centers of action located near ~25 and ~45 degrees during early and late boreal winter. Both structures are accompanied by eddy momentum flux anomalies that exhibit a remarkable degree of hemispheric symmetry. In the SH, the extratropical signature of ENSO projects strongly onto to the primary mode of large-scale variability, the Southern Annular Mode (SAM). During the austral summer, roughly 25% of the temporal variability in the SAM is linearly related to fluctuations in the ENSO cycle. An analogous relationship is not observed in association with the principal mode of climate variability in the NH, the Northern Annular Mode (NAM).
It is argued the seasonally varying impact of ENSO on the extratropical circulation is consistent with the impact of the thermally forced subtropical wind anomalies on the dissipation of equatorward propagating wave activity at subtropical latitudes.
Title: The Influence of the Mean State on the Annual Cycle and ENSO Variability: A Sensitivity Experiment of a Coupled GCM
Speaker: Dr. Julia Manganello
Affiliation: Climate Dynamics Program, George Mason University
Date: January 27, 2006 11:00 a.m.
Abstract: Simulation of the annual-mean climate, seasonal and interannual
variability in the tropical Pacific is compared in two versions of a coupled
ocean-atmosphere general circulation model (CGCM). The component models in
these two versions of the CGCM are identical: the atmospheric model is
Version 2 of the Center for Ocean-Land-Atmosphere Studies (COLA) Atmospheric
GCM, the oceanic GCM is a nonlinear reduced-gravity model of quasi-isopycnal
layers. The only difference between them is the coupling strategy. In the
first, component models are directly coupled over nearly global domain. In
the second, a prescribed empirical surface heat flux correction term based
on the mean sea surface temperature (SST) bias of the first model run, is
added to the prognostic SST equation. This correction term is constant in
time but varies spatially, and is proportional to the annual mean local SST
As expected, the addition of the empirical correction term eliminates major
mean SST errors, especially the warm bias near the southeastern coast of the
Pacific and Atlantic Oceans. Preliminary analysis shows that in the
southeast Pacific this climate drift could be associated with the simulation
of the wrong type of cloud cover. The corrected mean climate exhibits
stronger asymmetry relative to the equator, characteristic of these regions.
Due to the improvement of the model mean state, the annual cycles of the SST
and surface wind stress in the eastern equatorial Pacific become more
realistic as a result of enhancement of their annual, rather than
semi-annual, harmonics. The annual cycle of precipitation in the eastern
Pacific is also improved due to more realistic seasonal SST variations in
this region.
Both runs simulate interannual variability in the tropical Pacific with some
characteristics of ENSO. However, in the CGCM without flux adjustment phase
locking of ENSO to the annual cycle is unrealistic; ENSO events exhibit an
eastward propagation at the equator and show a double-peak feature in the
east connected to two distinct pulses in the zonal wind stress in the west.
As a result of flux adjustment, phase locking to the annual cycle is
reproduced remarkably well in the model, SST anomalies clearly exhibit a
standing mode at the equator, and the development of ENSO events at the
equator is also more realistic. On the other hand, the simulated
interannual variability is weaker and the timescale of ENSO events is longer
compared to the observations. High-latitude teleconnection patterns are
also not reproduced very well. Flux correction does not lead to
improvements in these aspects.

The Indian Ocean Dipole/Zonal Mode in the GFDL Coupled Model

Speaker: Qian Song
Affiliation: GFDL, Princeton University
Date: February 9, 2006 1:00 p.m.

In this study we investigate the Indian Ocean Dipole/Zonal Mode (IODZM) in a 250-yr simulation of the GFDL coupled global general circulation model (CGCM). The CGCM successfully reproduces many fundamental characteristics of the climate system of the Indian Ocean. We explore the character of the IODZM, and relationships between positive IODZM and El Niño events through a composite analysis. The IODZM events in the CGCM grow through feedbacks between heat-content anomalies and SST-related atmospheric anomalies, particularly in the eastern tropical Indian Ocean. The composite IODZM events that co-occur with El Niño have stronger anomalies and sharper east-west SSTA contrast than those that occur without El Niño. IODZM events, whether or not they occur with El Niño, are preceded by distinctive Indo-Pacific warm pool anomaly patterns in boreal spring: in the central Indian Ocean easterly surface winds, and in the western equatorial Pacific an eastward shift of deep convection, westerly surface winds and warm sea surface temperature. However, delayed onset of the anomaly patterns (e.g. boreal summer) are often not followed by IODZM events. The same anomaly patterns often precede El Niño, suggesting that the warm pool conditions favorable for both IODZM and El Niño are similar. Given that IODZM events can occur without El Niño, we propose that the observed IODZM-El Niñ o relation arises because the IODZM and El Niñ o are both large-scale phenomena in which variations of the Indo-Pacific warm pool deep convection plays a central role. Yet each phenomenon has its own dynamics and lifecycle, allowing each to develop without the other.

Title: Precipitation and water vapor: Their temporal-spatial behavior and use in
monsoon onset/retreat
Speaker: Er Lu
Affiliation: Dept of Atmospheric Science, University of Arizona
Date: February 9, 2006 3:30 p.m.
Abstract: Precipitation (P) and precipitable water (W) are important components of
the hydrological cycles in the earth system, and are closely related to
monsoon circulations over monsoon regions. By using W, a novel unified
method is proposed to determine the global monsoon onset/retreat. The
results are consistent with those obtained from different local criteria,
though the global monsoon regions cannot be fully determined. Theoretical
and data analyses demonstrate that, because of the large annual range of
temperature, W always increases from winter to summer anywhere except in
tropics, including both monsoon and nonmonsoon regions. In contrast, P
has different seasonal patterns, which can be understood from the
comparative strengths of the changes in water vapor and temperature. In
monsoon regions, the change of water vapor from winter to summer is much
greater than the change of temperature, so P has an in-phase relation
with W. While in some of the nonmonsoon regions, where winter is the
rainy season, the change of temperature is much greater than the change
of water vapor, leading to an out-of-phase relation between P and W. The
comparison of the behaviors of P and W suggests that W has the ability to
indicate both the means and the interannual variations of the monsoon
onset/retreat, while the global monsoon regions cannot be obtained from
W. Other results regarding Asian monsoon circulation and precipitation
may also be presented.
Title: ENSO oscillation and the decadal variation
Speaker: Dr. Kiku Miyakoda
Affiliation: Atmospheric and Oceanic Sciences Program, Princeton University
Date: March 17, 2006 11:00 a.m.
Title: Investigation of seasonal prediction of the South American regional climate using the nested model system.
Speaker: Fernando De Sales
Affiliation: UCLA
Date: February 23, 2006 3:30 p.m.

The NCEP regional Eta model was nested in the NCEP atmospheric general circulation model (AGCM) to provide a general assessment of the dynamic downscaling method in seasonal climate simulations over South America (SA). Both models were initialized with same initial conditions taken from the NCEP/NCAR reanalysis. The results showed that the nested model improved the simulation of seasonal mean lower- and upper-level circulations in both warm and cold seasons when compared to the AGCM alone. The nested model also produced better simulations of seasonal mean 2-meter temperature and precipitation. The improved resolution topography in the nested model substantially enhanced the SA low-level jet circulation, resulting in a better prediction of daily precipitation over the subtropics and eastern Brazil. However, the simulation of the ITCZ by the nested model was weak due to weak moisture convergence at low-levels. A possible cause for this deficiency is presented. The interannual and intraseasonal variability of the wind circulation, surface temperature, and precipitation were also examined. The nested model significantly improved the differences in the lower- and upper-level circulations between the summers of 1997-98 and 1988-89.   Furthermore, it captured the differences in precipitation over eastern and southern SA, which were neither simulated by the AGCM, nor depicted in the NCEP/NCAR reanalysis data.

Title: The Relevance of Entropy in Modeling and Studies of Weather and Climate:
Lessons We Should Have Learned Had We Paid Attention in School
Speaker: Prof. Donald Johnson
Affiliation: NCEP Special Project Scientist
Date: March 29, 2006 2:30 p.m.

The focus of this presentation will be on the estimation of Lagrangian entropy sources as a means to assess both the accuracies and uncertainties of models in the simulation of weather and climate. In an 1960 lecture at the Princeton Institute for Advanced Studies, von Neumann commented that numerical weather prediction was less difficult than modeling climate, while the most difficult challenge would be to bridge time and space scales in the modeling of weather and climate. The underlying reason for this assessment was that success in numerical weather prediction was critically dependent on the initial state, success in simulating climate was critically dependent on specifying boundary layer processes, while bridging of time and scales of weather and climate would depend on the complementary linking of internal and boundary processes.

NCEP’s emphasis is that success in modeling climate depends on success in modeling weather, a position dear to my interests and focus. A key aim in this lecture is to utilize Carathéodory’s statement of the Second Law in motivating the relevance of entropy and its change as a fundamental property in numerical simulations of weather and climate, both theoretically and pragmatically. The theoretical motivation embeds Carathéodory’s perspective in a basis relation regarding initial and final states with respect to attainable states, which can be reached by isentropic processes, and also the difference between states that can only be reached by non isentropic processes from those which cannot be reached at all.

The pragmatic motivation utilizes Carathéodory’s perspective of attainable and unattainable states to examine and quantify relative to truth the accuracies of models as a function of numerics, parameterizations all or in part, resolution, as well as the interrelation of these factors and others. Accuracies relative to truth can then be ascertained from the relative capabilities of models to simulate thermodynamic processes involving reversibility and irreversibility.

Then the equivalence that of simulating climate regionally and globally with the initial value problem of weather will be supported by utilizing Carathéodory’s insight concerning attainable and unattainable states. Here the age old concept of air masses, their transport and modification in terms of potential and equivalent potential temperature as the proxies for dry and moist entropy will be briefly reviewed and brought to bear. The results of the overall analysis provide the means to; 1) study the issue of biases and statistical uncertainity in models, 2) investigate why modeling of hydrological processes is so difficult and 3) determine inaccuracies from numerics alone and then from the interaction of numerics and parameterizations.

Title: Climate and Ecosystem Variability: Forcings and Feedbacks
2006 AMS Walter Orr Roberts Interdisciplinary Science Lecture
Speaker: Prof. Antonio J. Busalacchi
Affiliation: Earth System Science Interdisciplinary Center, University of Maryland
Date: April 4, 2006 10:00 a.m.
Abstract: A fundamental part of the Global Earth Observation System of Systems is its focus on observations ranging from weather and climate information to that for terrestrial ecosystems, marine ecosystems, and agriculture. At the present time, the major numerical weather prediction centers are moving toward a unified suite of forecasts using the same class of models for weather prediction, climate prediction, and climate change projections. The anticipated benefits of such forecasts extends from the protection of life and property to agriculture, ecosystems, health, and the environment. Yet, if we look critically at these forecast systems, and present day efforts in a predictive sense, they are really focused on the physical climate system and its coupling across the atmosphere, ocean, land surface, and cryosphere. New structures such as NOAA’s Climate Test Bed have been put in place to accelerate the transition of research and development into improved operational forecasts with long-term plans for advanced forecast capabilities for ecosystems, air chemistry, carbon cycle, fisheries, etc. This presentation will discuss some of our efforts at ESSIC that are at the intersection of the physical climate system and marine and terrestrial ecosystems.
Title: Towards Prediction of the Full Probability Distribution of Seasonal Climate
Speaker: Dr. Lisa Goddard
Affiliation: The International Research Institute for Climate and Society
Date: May 9, 2006 11:00 a.m.
Abstract: Recent effort at the IRI has been directed towards producing the full probability distribution of the climate so that users of the information can examine the categories or thresholds that are most meaningful to their decisions. In this talk I will present work in progress on diagnosing and 'fixing' conditional as well as systematic biases in dynamical seasonal climate predictions. In this context, I will also touch on the issue of ensemble size, and will emphasize the need for reliability, especially for the extremes of the seasonal distribution.
Title: Roles of the equatorial waves and western boundary reflection in the seasonal circulation of the equatorial Indian Ocean
Speaker: Prof. Donglian Yuan
Affiliation: Institute of Oceanology, Chinese Academy of Science
Date: May 18, 2006, 11:00 a.m.

An ocean general circulation model (OGCM) is used to
study the roles of equatorial waves and western
boundary reflection in the seasonal circulation of the
equatorial Indian Ocean. The western boundary
reflection is defined as the total Kelvin waves
leaving the western boundary, which include the
reflection of the equatorial Rossby waves as well as
the effects of longshore winds, off-equatorial Rossby
waves, and nonlinear processes near the western
boundary. The evaluation of the reflection is based
on a wave decomposition of the OGCM results and
experiments with linear models. It is found that the
longshore winds along the east coast of Africa and the
Rossby waves in the off equatorial areas contribute
significantly to the annual harmonics of the
equatorial Kelvin waves at the western boundary. The
semi-annual harmonics of the Kelvin waves, on the
other hand, originate primarily from a linear
reflection of the equatorial Rossby waves.

The dynamics of a dominant annual oscillation of sea
level co-existing with the dominant semi-annual
oscillations of surface zonal currents in the central
equatorial Indian Ocean are investigated. These sea
level and zonal current patterns are found to be
closely related to the linear reflections of the
semi-annual harmonics at the meridional boundaries.
Because of the reflections, the second baroclinic mode
resonates with the semi-annual wind forcing, i.e. the
semi-annual zonal currents carried by the reflected
waves enhance the wind-forced currents at the central
basin. Due to the different behavior of the zonal
current and sea level during the reflections, the
semi-annual sea level of the directly forced and
reflected waves cancels each other significantly at
the central basin. In the meantime, the annual
harmonic of the sea level remains large, producing a
dominant annual oscillation of sea level in the
central equatorial Indian Ocean.

The linear reflection causes the semi-annual harmonics
of the incoming and reflected sea level enhance each
other at the meridional boundaries. In addition, the
weak annual harmonics of sea level in the western
basin, resulting from a combined effect of the western
boundary reflection and the equatorial zonal wind
forcing, facilitate the dominance by the semi-annual
harmonics near the western boundary in spite of the
strong local wind forcing at the annual period.
The Rossby waves are found to have a much larger
contribution to the observed equatorial semi-annual
oscillations of surface zonal currents than the Kelvin
waves. The westward progressive reversal of seasonal
surface zonal currents along the equator in the
observations is primarily due to the Rossby wave

Title: The Euro-Mediterranean Center on Climate Change: a New Italian Initiative
Speaker: Dr. Antonio Navarra
Affiliation: Instituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy
Date: May 31, 2006, 2:00 p.m.
Title: The Role of the Thermohaline Circulation in Past and Future Climate Changes
Speaker: Dr. Jianjun Yin

Program in Atmospheric & Oceanic Sciences, Princeton University, GFDL, NOAA

Date: June 8, 2006, 11:00 a.m.

The Atlantic thermohaline circulation (THC) is an important part of the Earth's climate system. Previous research has shown large uncertainties in simulating the dynamical behavior, future evolution and climate impact of the THC. The simulated response of the THC to freshwater perturbations and the associated climate changes have been intercompared among 14 climate models over the world. The robustness of particular simulation features has been evaluated across the model results.   In response to 0.1 Sv freshwater addition in the northern North Atlantic projected under realistic CO 2 scenarios , the multi-model ensemble mean THC weakens by 30% after 100 years. No model simulates a complete shutdown of the THC. The surface air temperature presents a complex anomaly pattern and the Atlantic ITCZ tends to shift southward.   In response to 1.0 Sv freshwater input that resembles the past melting water pulses from the paleo-glaciers , the THC shuts down rapidly in all models. The resultant global-scale climate changes are considerable. Models disagree in terms of the bi-stability of the THC. The THC is bi-stable in one model group but mono-stable in the other model group. The differing dynamical properties of the THC are closely related to the formation and stability of a reversed thermohaline circulation (RTHC) in the South Atlantic Ocean. The role of the RTHC in causing the differing simulations of the THC is analyzed in detail.

Title: Climate downscaling: The value added using regional dynamical models
Speaker: Dr. Liqiang Sun
Affiliation: The International Research Institute for Climate and Society
Date: June 9, 2006, 11:00 a.m.

The increasing demand by the scientific community, policy makers, and the public for localized climate information has rendered the need for climate downscaling. High-resolution Regional Climate Models (RCMs) have been extensively used for climate downscaling over many regions around the world. This presentation summarizes the values added by dynamical downscaling using RCMs. The discussion focuses on subseasonal to interdecadal time scales, including 1) improvement of spatial patterns; 2) predictability at smaller spatial and temporal scales; 3) dynamical downscaling seasonal forecasts; and 4) interdecadal variability, and 5) a brief consideration of the coming decades that seeks to improve the climate dynamical downscaling.

Title: NCEP Update: Review of Progress in Operational Weather, Climate and Ocean Forecasts
Speaker: Dr. Louis Uccellini
Affiliation: Director - National Center for Environmental Prediction (NCEP)
Date: June 20, 2006, 11:00 a.m.

The presentation will focus on recent advances in NCEP prediction services related to operational weather, climate and ocean forecasts systems and cover such topics as the push to dynamical modeling in the SI range, the increasing emphasis on multi model ensembles for an increasing array of forecast applications with examples shown from this past winter, the application of Test Beds and Joint Centers throughout NCEP and an update on the new NOAA Center for Weather and Climate Prediction near the University of Maryland.

Title: Eddy- zonal flow feedback in Southern Hemisphere winter and summer
Speaker: Dr. Xiaosong Yang
Affiliation: ITPA/ Marine Science Research Center, SUNY at Stony brook, NY
Date: June 22, 2006, 11:00 a.m.

The eddy- zonal flow feedback in SH winter and summer is investigated in this study. The persistence timescale of the leading principal components (PCs) of the zonal mean flow shows substantial seasonal variations. In SH summer, the persistence timescale of PC1 is significantly longer than that of PC2, while the persistence timescales of the two PCs are quite similar in SH winter. Storm track modeling approach is applied to demonstrate that seasonal variations of eddy-zonal flow feedback for PC1 and PC2 account for the seasonal variations of the persistence timescale. The eddy feedback timescale estimated from a storm track model simulation and a wave response model diagnostic quantitatively shows that PC1 in JJA and DJF, and PC2 in JJA, have significant positive eddy-mean flow feedback, while PC2 in DJF has no positive feedback. The consistency between the persistence and eddy feedback timescales for each PC suggests that the positive feedback increases the persistence of the corresponding PC, with stronger (weaker) positive feedback giving rise to a longer (shorter) persistence timescale.
EP-flux diagnostics have been performed to demonstrate the dynamics governing the positive feedback between eddies and anomalous zonal flow. The mechanism of the positive feedback, for PC1 in JJA and DJF and PC2 in JJA, is as follows: enhanced baroclinic wave source (heat fluxes) at low level in the region of positive wind anomalies, propagate upward and then equatorward from the wave source, thus giving momentum fluxes that reinforce the wind anomalies. The difference of PC2 between DJF and JJA is because of the zonal asymmetry of climatological flow in JJA. For PC2 in DJF, wind anomalies reinforce the climatological jet, thus increasing the barotropic shear of jet flow. The “barotropic governor” plays a role in suppressing eddy generations for PC2 in DJF and thus inhibiting the positive eddy-zonal flow feedback.

Title: Problems and Prospects of Simulating Aerosol-cloud-radiation Interaction for Water, Mixed Phase, and Ice Clouds in GCMs
Speaker: Dr. Yogesh Sud
Affiliation: Laboratory for Atmospheres, Goddard Space Flight Center, Greenbelt, Maryland
Date: June 23, 2006, 11:00 a.m.

Presently, the direct effect of aerosols has been included in many GCMs and this helps to better simulate incoming surface solar radiation. In fact,even this parameterization requires "difficult-to-prescribe" space-time
distribution of particle sizes, mass-load, and optical properties of several key atmospheric aerosol species (that change with age). Nevertheless, the "indirect effect" of aerosols is even more important because it affects the cloud particulate number density, life-time, in-cloud water amounts, and precipitation efficiency, all of which
impact the simulated cloud-radiative forcing of water, mixed phase and ice clouds. Of these, only the physics of cloud-droplet formation and rainfall production in water clouds is well understood, however even this is
lacking in many GCMs. We have been developing a scheme to represent aerosol water-cloud interaction in our GCM. Our CCN activation scheme is due to Nenes and Seinfeld (2003) that was subsequently simplified for
log-normally distributed aerosols (Fountoukis and Nenes, 2005). It interacts with state-of-the-art microphysics algorithms due to Seifert and Beheng (2001, 2006). Simulation results of water-cloud aerosol interaction in the
ARM-SCM evaluation and validation with the ARM-SGP data will be shown. The parameterization of mixed-phase and ice clouds is even more challenging; some potentially useful constructs of Liu and Penner (2005) will be
discussed. Indeed, a number of modeling assumptions still need to be anchored to the observations as well as need reconfirmation through aerosol-chemistry-cloud microphysics models and performance evaluation
against analyzed clouds and aerosols climatologies.

Title: Development in Africa - a view on the role and improvement of seasonal predictions
Speaker: Dr. Mike Harrison
Affiliation: Hadley Center, UK Met Office
Date: June 27, 2006, 3:00 p.m.


Title: Dust Storm, the Mechanism of Dust Emission and their Predictions
Speaker: Dr.Q. C. Zeng
Affiliation: Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Date: July 17, 2006, 3:00 p.m.

Dust storm is a very severe disastrous weather system consisting of strong wind, soil erosion, air pollution by dust particles, and very low visibility. Satellite image can present the gigantic picture of dust storm. In order to make numerical-dynamical prediction of dust storm, we should develop a dust emission and transport model and couple it with a weather forecasting model with good enough treatments of atmospheric boundary layer and land surface processes. The mechanism of dust emission takes the central part in such a dust model. We discovered that wind gust and its relevant coherent disturbances in the atmospheric boundary layer play a crucial role in the dust emission and its penetration into the troposphere from the boundary layer. A parameterization scheme of gust effect was then developed and applied to the model. Furthermore, the climatic conditions favorable for the frequent occurrence of dust storms in the spring in East Asia were investigated, and preliminary results of dynamical prediction (for two seasons) of such climate situations were encouraging.

Title: Regional Climate Modeling: Recent Development and Applications
Speaker: Dr. Lai-Yung (Ruby) Leung
Affiliation: Pacific Northwest National Laboratory
Date: August 4, 2006, 11:00 a.m.

Climate varies across a wide range of temporal and spatial scales. Yet, climate modeling has long been approached using global models that can resolve only the broader scales of atmospheric processes and their interactions with land, ocean, and sea ice. Clearly, large-scale climate determines the environment for mesoscale and microscale processes that govern the weather and local climate, but, likewise, processes that occur at the regional scale may have significant impacts on the large scale circulation. Resolving such scale interactions will lead to much improved understanding of how climate both influences, and is influenced by, human activities.

Since the early 1990s, regional climate models have been used as a downscaling tool to study regional climate processes and provide regional climate information such as climate change projections and seasonal climate predictions for assessing climate impacts. In this presentation, I will summarize a number of regional climate modeling studies that we have performed to understand the effects of climate variability and change at the regional scale, with more focus on the western U.S. where the strong topographic influences on regional climate necessitate the need for regional climate information. I will also summarize some recent efforts on developing and applying the Weather Research and Forecasting (WRF) model to study regional climate. In particular, I will present preliminary results of applying WRF to simulate tropical convection and tropical modes using a channel model configuration. Future plans in using regional climate models to address both downscaling and upscaling issues will also be discussed.