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Sort by: Title Principal Investigator (s) Task Force Year Initially Funded
Year Initially Funded: 2010
Task Force:
Final Report:
Karnauskas_Final_Report.pdf

The American Midsummer Drought: Causal Mechanisms and Seasonal–to–Interannual Predictability

View abstract

The Intra–Americas Sea (IAS) region– including the northeastern tropical Pacific Ocean, Caribbean Sea, Gulf of Mexico, western tropical Atlantic Ocean, and all adjacent landforms–represents a fascinating natural climate laboratory due to a confluence of diverse oceanic, orographic, atmospheric, and remote influences. The IAS region is also home to a large portion of humanity whose livelihood depends critically upon the spatiotemporal variability of precipitation. Throughout most of the IAS region, the rainy season spans roughly May through October with a break in precipitation in July–August known as the midsummer drought (MSD). This feature of the rainfall climatology is highly unique to the IAS region, and is particularly evident over Central America and the adjacent northeastern tropical Pacific Ocean. Indeed, the MSD is such a pervasive phenomenon that crop insurance programs incorporate what little information is known of the MSD in pricing and triggering policies in Central America. Since the recognition of the MSD as a regular climatological feature in the early 1960s, much effort has been directed toward characterizing and understanding the MSD. Both local processes (e.g., SST–convection–radiation feedback) and aspects of the general circulation (e.g., the North Atlantic subtropical high) have been shown to influence the MSD. To date, however, a unifying explanation for the very existence of the MSD has yet to emerge. As a result, our understanding of the interannual variability and– most importantly– predictability of the MSD is only in a nascent stage. Seasonal–to–interannual climate predictions for the IAS region would benefit greatly from an understanding of the causal mechanisms for the existence and variability of the MSD. We propose to first focus on analysis of observations: satellite and in situ measurements, as well as state–of–the–art global and regional reanalyses to diagnose the dominant mechanisms of the MSD in the IAS region. Secondly, we will use state–of–the–art general circulation models to test specific hypotheses regarding the dominant mechanisms of the MSD and its variability. This approach will allow us to thoroughly examine and identify the features of the global atmospheric circulation and, especially, the role of the ocean, that are crucial for predicting seasonal hydroclimate variability in the IAS region.


Principal Investigator (s): Karnauskaus, Kristopher (WHOI)

Co-PI (s): Giannini; Seager, Richard (Columbia University; Busalacchi, Tony (University of Maryland/ESSIC)
Year Initially Funded: 2010
Task Force:
Final Report:

Climatic Predictability of Extreme Floods in the United States

View abstract

Of all climate-related disasters, floods account for the largest average annual losses. Only a limited climatic perspective on floods in the United States exists. This includes the identification of the seasonality and typical mechanisms (e.g., frontal or connective precipitation) important for floods by subregion. Climate change analyses have led to either no clear assessment of changes in flood potential, or to projections of dramatically increased frequency of extreme floods. The anticipated intensification of the atmospheric hydrological cycle and the increased atmospheric moisture holding capacity under warming, render increasing flood risk plausible. However, it is unclear whether the climatic processes associated with extreme floods are well modeled in global and regional climate models, and whether such models provide predictability for assessing the frequency and intensity of rainfall responsible for extreme floods in the United States with spatial specificity relevant for hydrological analysis of floods.

Our work shows that extreme floods (annual exceedance probability less than ~ 0.1) in most river basins in the United States are associated with a distinct atmospheric moisture transport pattern, where the moisture source is typically in the oceans rather than associated with local convection. Over much of the Western United States, we have been able to demonstrate statistical predictability of the annual maximum flood conditional on pre-season Pacific SSTs. For a region in Brazil we are able to demonstrate that the annual maximum flood at each of the stations can be modeled using concurrent large scale, seasonal climate predictors, and a spatial scaling model for the flood process indexed to the drainage area of the site. Consequently, our hypothesis is that river basins aggregate the spatio-temporal climate signal in terms of synoptic and seasonal atmospheric moisture transport in a way that allows empirical connections to be drawn between slowly varying climate fields and the severity, incidence and location of extreme floods over N. America. If these connections can be quantitatively assessed, modeled and understood, then a basis for assessing changes in flood risk using GCMs or empirical methods could be developed for seasonal prediction and for climate change projections.

The research proposed here seeks to develop an exploratory statistical-dynamical approach for “downscaling” flood risk from climate models through an analysis of the causal structure of the entire ocean-atmosphere-land chain of the flood process. This entails (a) use of historical, reanalysis and GCM data for the diagnostic analyses of the causal structure from the spatiotemporal hydroclimatic data associated with the extreme floods in each of the regions of the United States; (b) Bayesian model development for assessing the conditional probability distributions across the causal chain, leading to a conditional flood risk estimate given either GCM state variables or observed/re-analysis data fields, and (c) assessments of projections of flood risk at selected locations for the upcoming season or for a climate change scenario.


Principal Investigator (s): Lall, Upmanu (IRI/Columbia University)

Co-PI (s): Kushnir, Yochanan (IRI/Columbia University); Robertson, Andrew (IRI/Columbia University); Nakamura, Jennifer (IRI/Columbia University)
Year Initially Funded: 2010
Task Force:
Final Report:

Influence of Convective Systems on Intraseasonal to Interannual Variability of the Intra-American Monsoon

View abstract

We propose to examine the contribution from large-scale organized transient disturbances to intraseasonal and seasonal total rainfall of the intra-Americas Sea region (IAS). The focus will be on disturbances with periods of less than 30 days affecting the tropical regions from Mexico to northern South America. Kelvin waves, cold surges and easterly waves are of primary interest. A visual inspection of Hovmoeller diagrams reveals many examples of Kelvin disturbances that form near the dateline and propagate eastward. When they encounter South America, convection - as depicted by outgoing longwave radiation (OLR) - typically increases over tropical regions. These disturbances propagate into the Atlantic, where they substantially affect the intertropical convergence zone there (Wang and Fu 2007). Kelvin waves can also form in-situ over the Amazon basin during southern summer when cold surges originating in the middle latitudes of South America force convection at the Equator (Liebmann et al. 2008). During southern winter, when cold surges are stronger and Amazon convection is weak, they frequently propagate across the Equator and into the Caribbean. Mesoscale convective activity is seen to be significantly modulated by equatorial waves, and this will also be examined in some detail. Our initial analyses indicate that convective activity is enhanced when westward propagating disturbances encounter Kelvin waves and cold surges. It is likely that problems in representation of the climate of the IAS by models suffer from an incorrect representation of subseasonal disturbances. In addition to analyzing the aforementioned disturbances in observations, a similar analysis will be made for the coupled general circulation models that will constitute the basis of the Intergovernmental Panel on Climate Change 5th Assessment Report.

The questions we propose to address are the following:

1) What is the seasonal cycle and interannual variability of Kelvin wave activity, and how is Kelvin wave activity related to large-scale, slowly varying phenomena?

2) How do Kelvin and other equatorial waves modulate mesoscale variability and the diurnal cycle?

3) Although transients are prominent in satellite-based observations of cloud top such as OLR, to what extent do they account for seasonal totals in the IAS?

4) Do westward propagating disturbances amplify or diminish when they encounter Kelvin waves or cold surges from either hemisphere?

5) Where are the transients that affect the IAS initiated?

6) Do coupled atmosphere-ocean models represent well the subseasonal transients, and to what extent do errors in their climatology result from problems in representing these disturbances?

7) Can rainfall be predicted with skill for several days in advance from trajectories of disturbances as they approach the IAS?

Principal Investigator (s): Liebmann, Brant (CIRES Climate Diagnostics Center)

Co-PI (s): Kiladis, George (NOAA/ESRL); Vera, Carolina (University of Buenos Aires)
Year Initially Funded: 2010
Task Force:
Final Report:

Drizzle and Cloudiness Transitions in Southeast Pacific Marine Stratocumulus

View abstract

The representation of boundary layer clouds in global climate models (GCMs) has been identified as a leading cause driving uncertainties in future climate change scenarios. Low cloud properties are highly variable in space and time, with the climatically important shortwave cloud forcing differing widely between cloudy and clear regions. Mostly visibly notable in marine boundary layer systems are pockets of open cells (POCs), regions of low cloud fraction, high precipitation rate, and low aerosol concentration, most commonly embedded in extensive regions of solid stratocumulus. The casual mechanisms explaining the evolution from solid cloud to POC, however, are not well understood. Specifically of interest are the transition regions between solid and broken cloud, since these are thought to be the focal point for driving mesoscale variability.

The Variability of the American Monsoon Systems [VAMOS] Ocean-Cloud-Atmosphere-Land Study -- Regional Experiment (VOCALS-Rex) field campaign took place over the southeast Pacific (SEP) region during Oct-Nov 2008. The proposed research takes advantage of the fact that the C-band radar on board the NOAA R/V Ronald H. Brown was the sole observational platform in VOCALS able to sample the near-instantaneous three-dimensional mesoscale structure of the precipitation field, while also capturing evolution of individual cells over their lifecycles. The VOCALS radar observations include an unexpected discovery: the frequent occurrence of regions of very high reflectivity (>40 dBZ), untruecedented for boundary layer clouds. The VOCALS data, along with preliminary simulations, suggests the following overarching question: Fundamentally, what drives cloud system variability in marine boundary layer clouds?

The proposed research seeks to evaluate, in a numerical modeling framework, various hypotheses related to boundary layer drizzle processes and cloud variability over the SEP. These hypotheses are formulated to address the following questions directly related to SEP cloud systems: i. What are the leading factors in establishing drizzle and mesoscale cloud variability?; ii. What are the predominant mechanisms active at the transition between solid stratocumulus and POCs?; iii. What are the dynamic and microphysical processes associated with cloud field evolution from unbroken stratocumulus to POC and back to solid cloud? The study proposes a "near-LES" simulation framework, combined with observational constraint on the model.

This proposal direction addresses the CPPA goal to "improve understanding and process modeling of cloud, planetary boundary layer, and microphysics…," with the VOCALS field campaign being specifically mentioned in the original call. Furthermore, this proposal would leverage undergoing CPPA-funded work, particularly the ship-based observational efforts.


Principal Investigator (s): Mechem, D. B. (University of Kansas)

Co-PI (s):
Year Initially Funded: 2010
Task Force:
CMIP5 Task Force
Final Report:

North America Hydroclimate Variability in CMIP5 Model Climate Simulations and Projections: Are Simulations Improving and Projections Converging?

View abstract

Analysis of simulations and projections of regional hydroclimate variability over North America, especially the Central United States (U.S)., from the CMIP3 models indicate that the region imposes a notable challenge for global climate models. Difficulties arise due to the imperfect representation of processes that generate precipitation variability over the Central U.S. and the lack of consistent projections of tendencies and extremes in summer from the models analyzed. 

We propose a two tier analysis for the climate simulations and projections from the models participating in the new CMIP5 effort: An extensive evaluation and intercomparison of tendencies and extremes in projections from pentad to seasonal scales, and analysis of the mechanisms that generate summertime precipitation variability over the Central U.S.. Convergence of tendencies and extremes among the models will give some certainties to our societies, while a good assessment of the mechanisms in the models will give reassurance in the projections. The projections to be analyzed will be those emanated from the new scenario given by the Representative Concentration Pathway 8.5 which is characterized by increasing greenhouse gas emissions in the 21st century.

The analysis of mechanisms that generate precipitation variability over the Central U.S. in summer will be based of the analysis of the structure of the components of the atmospheric water balance in model simulations and projections. The main mechanism will be revealed by the relative magnitude of the regressions of regional precipitation indices on precipitation, moisture fluxes, and evapotranspiration; this analysis will be complemented with a correlation analysis of July precipitation with the previous months’ precipitation, to assess, indirectly, the strength of soil moisture feedback. Because observations indicate that precipitation variability is generated by remote forcing, two different versions of empirical function analysis (EOF) will be employed to detect the main modes of variability in the simulated and projected climates: 1) a rotated EOF analysis of summer SSTs and 700hPa heights, and an Extended EOF analysis of SSTs. Comparisons with observations, especially in near-term projections will reveal the realism of the mechanisms generating regional hydroclimate variability in the models.

The analysis of tendencies will include the whole region, however, the analysis of extremes and droughts will be focused on the Central U.S.,with secondary attention on Southwestern U.S.. Credibility in the projected tendencies will be given by their proximity with those observed at the end of the 20th century. The assessment of extremes will be done at pentad, monthly and seasonal resolutions, but the assessment of droughts will be done at low-frequency scales of seasonal data via histogram analysis.


Principal Investigator (s): Ruiz-Barradas, Alfredo (University of Maryland); Nigam, Sumant (University of Maryland)

Co-PI (s):
Year Initially Funded: 2010
Task Force:
CMIP5 Task Force
Final Report:

Evaluation of the Tropical Storm Track Across the Intra-Americas Sea in IPCC AR5 Models and the Mechanisms of Change in a Warmer Climate

View abstract

The Intra-Americas Sea (IAS) includes the Gulf of Mexico, Caribbean Sea and tropical northeast Pacific Ocean, the latter of which is the most prolific hurricane formation region in the world per square meter. Heavy rains arrive over the IAS during boreal summer, when the Inter- Tropical Convergence Zone (ITCZ), or axis of the tropical storm track, migrates north off the equator and SSTs warm throughout the region. Localized moisture convergence over land areas within the IAS is important for hydropower, agriculture and fresh water supplies. IAS moisture transport into northern Mexico and Southwest U.S. is also important for agriculture and populations in these regions.

Several studies point out the critical role that orography plays in present day mid-latitude and tropical storm tracks. Recent work also suggests that the Caribbean low-level jet (CLLJ) influences storm track activity within the IAS. Studies of tropical storm tracks within the projected warmer conditions of the 21st century find reduced storm track activity in the tropical Atlantic and a shift of the tropical northeast Pacific storm track southward. The intensity of tropical storms overall appears to remain unchanged in studies that have accounted for a mean shift in the tropical mean sea surface pressure due to warmer temperatures. However, predicting storm intensity changes remains a difficult task, as this parameter is more dependent on model resolution than storm frequency.

The following questions are raised by these studies: i) Will the roles of orography and the CLLJ change if the storm track in the tropical eastern Pacific shifts southward in the 21st century? ii) How would such a change affect intensity of storms in the tropical eastern Pacific? iii) How would changes in the position of the tropical eastern Pacific storm track affect the precipitation over land areas of the IAS and NAM regions?

This study proposes to investigate these questions through the following set of analyses:

-Obtain 20th century tropical storm track statistics using state-of-the-art reanalyses.

-Assess tropical storm track statistics of all AR5 model 20th century scenario data available at greater than daily resolution against the reanalyses’ statistics.

-Use high-resolution regional model simulations to assess physical mechanisms associated with several real cases of developing and non-developing tropical depressions within the IAS using the reanalyses as boundary forcing for these simulations.

-Force the regional model for actual cases of 21st century storms/waves from AR5 models that produce realistic track statistics for the 20th century and compare mechanisms of storm initiation and intensification with the cases from step 3. 

This project will make use of a numerical technique in which actual features of the tropical storm track (easterly waves and mature storms) in the AR5 models will be simulated using a high-resolution regional model, rather than using idealized simulations of a mature tropical storm forced with the general conditions of a warmer climate. This approach permits changes in genesis mechanisms to be evaluated.


Principal Investigator (s): Serra, Yolande (University of Arizona)

Co-PI (s):
Year Initially Funded: 2010
Task Force:
Final Report:

Understanding atmosphere-ocean coupled processes in the southeast Pacific

View abstract

Coupled atmosphere-ocean general circulation models (CGCMs) have systematic errors in the southeast Pacific (SEP) region. The biases need to be traced back to specific model characteristics, such as certain aspect of the physical parameterizations, in order to provide useful guidance on how to improve the model simulation. The primary goal of this proposed study is to improve our understanding of the structure and mechanisms of CGCMs’ systematic biases in the southeast Pacific. To realize this goal, we need to examine, step by step, the key biases in its AGCM, the key biases in its OGCM, and the key biases in its ocean-atmosphere feedback processes when the AGCM and OGCM are coupled together. Therefore, we propose to:

(1) Diagnose the structure and mechanisms of the AGCM biases in stratocumulus/stratus clouds, marine boundary layer (MBL), and surface fluxes in the SEP region in IPCC AR5 CGCMs;

(2) Analyze the upper ocean currents, thermal structures and heat budget in the SEP region in IPCC AR5 CGCMs;

(3) Examine the ocean-atmosphere coupling processes in the SEP region in IPCC AR5 CGCMs, especially how well the ocean-atmosphere feedbacks are simulated; and

(4) Conduct forced OGCM experiments to examine the sensitivity of upper ocean processes to atmospheric forcings relevant to AGCMs’ biases.


Principal Investigator (s): Shinoda, Toshiaki (Navel Research Laboratory)

Co-PI (s): Lin, Jialin (Ohio State University)
Year Initially Funded: 2010
Task Force:
Drought Task Force
Final Report:

A framework for improving land-surface hydrologic process representation in CLM over California

View abstract

To address the Climate Prediction Project for the Americas (CPPA), formerly known as the Global Energy and Water Cycle Experiment (GEWEX) American Prediction Project (GAPP) research priority: “Climate-based hydrologic and water management applications at regional scales,” this proposal has selected California as a data-rich, high population, and scientifically productive study region. California’s wdater supply systems are straining to keep up with economic growth and urban development. The groundwater resource—which accounts for 30-40% of the water California uses -- is diminishing at a rate of millions of acre-feet per year. The state has experienced two major droughts and three major floods since 1980’s, and California continues to grow and build. Combined, these regional changes pose an urgent need for accurate models and reliable predictions of key hydrologic processes of regional climate change and guidance for California’s water management responses.

The UC Irvine Center for Hydrometeorology and Remote Sensing (CHRS) proposes to respond specifically to the call for “Efforts of development and improvement of integrated (i.e., coupled snow, surface water, soil moisture and groundwater) hydrologic models…data assimilations, model evaluations against high-resolution datasets, and parameterization of water management (e.g. irrigation, reservoir storage, and release, groundwater withdrawal etc.) for use in basin- to continental-scale models.” To address this challenge, proposed integrated hydrological models would include: 1) a remote sensing satellite-based snow model, 2) a modified Community Land Model (CLM) Land Surface Model (LSM), and 3) a two-dimensional MODFLOW (The USGS Modular ground-Water Model—the Ground-Water Flow Process). In addition to simulating the basic hydrologic processes, these coupled models will aim specifically to improve estimations of interactive mechanisms: snow cover and Snow Water Equivalent (SWE) estimation using in-situ and satellite data; the partition of snow water into runoff, soil moisture and groundwater recharge; parameterization of seasonal irrigation and groundwater pumping over the state, and groundwater discharge/recharge to/from river flows.

Among only a few U.S. states that have accumulated decades of ground-based water records, California maintains extensive networks for regular hydrological measurements. Taking advantage of California’s wealth of historical and current data, we propose to use long-term data for model parameter calibration and sequential data assimilation techniques to substantially improve model performance. Calibrating model parameters using information from long-term observations will optimize values for key model parameters, reducing model uncertainty. The sequential data assimilation technique—the Sequential Bayesian Filter with Monte Carlo implementation (SBF-MC) will integrate near real-time hydrological measurements from satellites (e.g. top layer soil moisture) and/or ground sites (e.g. stream gauge data and groundwater well monitoring) to both improve the predictions of model state variables and quantify prediction uncertainty.


Principal Investigator (s): Sorooshian, Soroosh (UC Irvine)

Co-PI (s):
Year Initially Funded: 2010
Task Force:
Final Report:

The Role of Land Surface Physics in Controlling Intraseasonal Precipitation Variability over Complex Terrain

View abstract

The prediction of hydrometeorological processes is hindered by the limited capabilities of integrated models that properly handle land surface physics in complex terrain. A key issue for improved intraseasonal simulations in western North America is capturing the variability in land surface conditions in mountain areas. Two of these areas – central Rocky Mountains in U.S. and Sierra Madre Occidental in Mexico – provide ideal areas for developing hydrometeorological model improvements as they span a clear hydroclimate gradient from cold to warm-season dominated regimes. Two related questions need to be addressed to enhance warm-season hydrometeorological forecasts in mountain regions: How do land surface conditions and their memory enhance or surpress convective precipitation in mountain regions? and How do variations in climate and vegetation along the continental hydroclimate gradient impact the relations between land surface physical processes and convective precipitation? Both questions are fundamental to understanding intraseasonal climate processes and improving operational models and their reanalysis products in the region.

Our proposal focuses on improved process simulations using hydrometeorological models in two mountain regions as proxies for similar systems across the North American hydroclimate gradient. We are especially interested in demonstrating how regional topographic features interact with the land surface state and its memory (soil moisture and temperature, vegetation and irrigation/reservoirs) to modify intraseasonal precipitation characteristics that control hydrologic response (flooding and drought). The study focuses on regions with low intraseasonal predictability in convective precipitation, soil moisture and streamflow, thus requiring new physical insight obtained from field data, remote sensing and numerical modeling. We will take advantage of intense observation and forecasting periods carried out by the proponents and an existing network of research and operational instruments. Our efforts are aimed towards improved characterization of intraseasonal variability in precipitation, land surface conditions and streamflow through use of two versions of a coupled hydrometeorological modeling system. 

To address the science questions outlined above, we propose the following project elements: (1) Hydrometeorological data collection and diagnostic analysis in the two mountain areas to define the characteristic behavior of the regional hydrometeorology and land surface conditions and construct an observational/reanalysis archive for model testing; (2) Conduct idealized hydrometeorological modeling experiments that mimic local topographic conditions and explore the impact of prescribed (and perturbed) land surface state variations in space and time on convective precipitation and its characteristics; and (3) Three-dimensional hindcast and forecast experiments using a coupled hydrometeorological model that incorporates key findings of the idealized model runs to demonstrate how different land surface physics in each region yield important up-scaled impacts on precipitation and streamflow variability at intraseasonal time scales. Comparison of the two mountainous regions along the hydroclimate gradient will allow a direct test of the relevance of land surface memory on intraseasonal precipitation variability.


Principal Investigator (s): Vivoni, Enrique (Arizona State University)

Co-PI (s): Gochis, David (NCAR)
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The Modeling, Analysis, Predictions, and Projections (MAPP) Program's mission is to enhance the Nation's capability to understand and predict natural variability and changes in Earth's climate system. The MAPP Program supports development of advanced climate modeling technologies to improve simulation of climate variability, prediction of future climate variations from weeks to decades, and projection of long-term future climate conditions. To achieve its mission, the MAPP Program supports research focused on the coupling, integration, and application of Earth system models and analyses across NOAA, among partner agencies, and with the external research community.

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