A41A-01
Pentad Evolution of the 1988 Drought and 1993 Flood over the Great Plains: A NARR perspective
The 1988 drought and 1993 flood in the central United States were among the most extreme climatic events in recent decades. The socioeconomic impact of these episodes was massive, with a price tag in the tens of billions of dollars and significant loss of life and property. Pentad (5-day averaged) evolution of these two events is studied using the 27-year precipitation assimilating North American Regional Reanalysis (NARR). The use of an improved hydroclimate dataset allows the rapidly evolving (sub-monthly) structure of the regional circulation and land surface anomalies during these two extreme events to emerge on a scale never before realized. This study focuses on the spatial and temporal relationships between the Great Plains low-level jet (GPLLJ), precipitation, and evaporation during MJJ in 1988 and 1993. The rapidly evolving hydroclimate anomalies reveal the dominance of GPLLJ induced moisture flux convergence over local precipitation recycling. Land-atmosphere impacts on GPLLJ modulation over the southern plains show a connection to a preferred mode of GPLLJ variability diagnosed through EOF analysis. While indicative of a land surface influence on the GPLLJ, the infrequent occurrence of this mode (12%) (as opposed to higher modes which are linked to large scale remote circulation variations) suggests the primacy of remote circulation influences in generating the GPLLJ and precipitation anomalies during extreme hydroclimatic events. July 1993 precipitation is linked to the antecedent winter ENSO and contemporaneous NAO further suggesting a role for known large scale climate variations on summertime North American extreme hydroclimate episodes.
A41A-02
Effects of ENSO, NAO (PVO), and PDO on Monthly Extreme Temperature and Precipitation
The El Nino-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and the Polar Vortex Oscillation (PVO) produce conditions favorable for monthly extreme temperatures and precipitation. These climate modes produce upper level teleconnection patterns that favor regional droughts, floods, heat waves, and cold spells, and these extremes impact agriculture, energy, forestry, and transportation. The above sectors prefer the knowledge of the worst (and sometimes the best) case scenarios. This study examines the worst and best case scenarios for each phase and the combination of phases that produce the greatest monthly extremes. Data from North America are gathered from the Historical Climatology Network (HCN), and data from these stations are bootstrapped in order to expand the time series. Bootstrapping is the stochastic simulation of monthly data by the utilization of daily data with identical ENSO, PDO, and PVO (NAO) characteristics. Because the polar vortex occurs only during the cold season, the PVO is used during January, and the NAO is used during other months. The bootstrapped data are arranged, and the tenth and ninetieth percentiles are analyzed. It has been found that the magnitudes of temperature and precipitation anomalies are greatest in the western Canada and the southeastern United States during winter, and these anomalies are located near the Pacific North American (PNA) nodes. Summertime anomalies, on the other hand, are weak because temperature variance is low. The magnitudes of the anomalies and the corresponding phase combinations vary regionally and seasonally.
A41A-03
A Strategy for Climate Change Experiments
Climate models used for climate change projections are on the threshold of including much greater biological and chemical detail. Today, standard climate models (referred to generically as atmosphere-ocean general circulation models, or AOGCMs) include components that simulate the coupled atmosphere, ocean, land and sea ice. Some modeling centers are now incorporating carbon cycle models into AOGCMs in a move towards an Earth System Model (ESM) capability. Additional candidate components for ESMs include aerosols, chemistry, and dynamic vegetation. This confluence of activities in model and scenario development must be communicated and coordinated across various groups and scientific communities. To this end, a strategy for the next generation climate simulations is discussed that: (1) identifies new components in preparation for inclusion in AOGCMs, (2) establishes communication for coordination through the World Climate Research Programme (WCRP), Integrated Geosphere-Biosphere Programme (IGBP) and the Integrated Assessment (IA) modeling teams, (3) proposes an experimental design for 21st century climate change experiments and (4) specifies the requirements for time series of constituents from new stabilization scenarios (particularly with regard to impacts, mitigation, and adaptation). Two timescales have been proposed for community coordinated climate change projection experiments: near term (to 2030) and longer term (2100 and beyond). The proposed short term simulations are designed to provide better guidance as to the likelihood of changes in climate extremes at regional scales. Meeting this challenge will depend on scientific questions involving understanding the processes that produce such extremes related to the hydrological cycle, and relevant atmospheric and oceanic processes operative on appropriate timescales. For long-term simulations (2100 and beyond) concentrations (rather than emissions from scenarios) through the coupled models will generate the compatible emissions that can be derived by, say WGIII. In light of the release of the recent IPCC AR4 results, we believe that this topic is highly relevant and of broad interest to the AGU community.
A41A-04
Intense and Extensive Summer Heat Waves Under Current and Possible Future Climates
The spatial scale of a heat wave is an important determinant of its impacts. Extensive summer heat waves are considered over Europe and North America in observations and model projections. Recent trends towards more frequent and extensive hot spells follow global warming trends, but are regionally modulated on decadal timescales. Model projections reflect these influences. Europe, warming continuously, had an early warning in 2003 of conditions projected for the second half of the 21st century. Until summer 2006, North America, in spite of a general summer warming, has not seen the extent of heat consistent with model projections. The recent warming over North America is unusual in that it occurred without the large-scale encouragement of a dry soil associated with precipitation deficit. Extensive and persistent heat waves naturally occur in association with widespread drought. Regional precipitation anomalies together with global anthropogenic influences can explain the atypical pattern of North American summer warming prior to 2006. Last summer's widespread heat waves were consistent with drier conditions over the Eastern US. Drought has the potential to seriously exacerbate the recent warming over North America to levels significantly in excess of the 1930s and in line with the warmest projections. Assuming realistic warming scenarios, a long-term anthropogenic increase (decrease) in the frequency and spatial extent of regional hot (cold) spells is projected to be strong and strongly modulated by decadal-scale variability throughout the 21st century.
A41A-05
Long-term Probabilistic Forecast and T* Distribution
Models are great tools to test ideas. Their usefulness, however, depends on their ability to simulate the current reality and predict the future. In this study, I show that a statistical model based on a new t*-distribution of station temporal data is capable of predicting the probability of any future outcome to exceed a specific value using only the currently available sample statistics assuming a normal random variable. In an air quality management application, the model has demonstrated categorically an average success rate of over 80 percent both in simulating the current ozone non-attainment areas and forecasting the rate of future violation of the 8-hour ozone National Ambient Air Quality Standards in the U.S. for up to 12 years. While the predictability of deterministic climate models is still limited by large uncertainties, the probabilistic forecast by this model provides a promising alternative in assessing the climate impact on environment for decades.
A41A-06
Development of a World Extreme Weather Archive
At a task meeting of the WMO OPAG 2 group, members unanimously agreed that the creation of a world archive for verifying, certifying and storing world weather extremes was useful and necessary. Consequently, the initial set of world records created by the WMO rapporteur for climate extremes includes the following global values: hottest temperature, coldest temperature, highest pressure, lowest pressure, greatest 1-minute, 1-hour, 12-hour, 24-hour and 1 year precipitation, greatest annual precipitation, heaviest hailstone, longest dry period, and maximum surface wind gust (non-tornado). In addition, a variety of official hemispheric and continental records are established. Finally, records for characteristics of tropical cyclones (e.g., deadliest, highest wind speed, largest eye, etc.) and tornadoes (e.g., deadliest, longest track, etc.) are also established.
A41A-07
Overview of the North America Climate Extremes Monitoring (NACEM) System
The IPCC Fourth Assessment Report and other climate assessments have documented an increasing trend in temperature and precipitation extremes, including hot days and nights, heavy precipitation events, and area affected by droughts. Extreme weather and climate events such as these often result in significant socioeconomic and environmental costs within affected areas. This reality along with the likelihood that trends toward more frequent and intense extreme events will increase in a warming world has focused attention on programs that can provide information to decision makers responsible for planning, response, and mitigation activities. Several government and university institutions throughout the U.S., Canada, and Mexico have partnered to improve monitoring of extremes across the North American Continent. This effort began in late 2002 with establishment of the North America Drought Monitor (NADM), an operational program for monitoring continent-scale drought conditions on an ongoing basis. Following the NADM, this trilateral partnership initiated development of a web- based climate extremes system to expand the capacity to monitor a wider range of climate extremes. Using daily data from stations across these three countries, the North American Climate Extremes Monitoring (NACEM) system now provides decision makers with the ability to monitor and analyze climate extremes on the continent. The U.S. and Canada are also collaborating in the creation of a near-real time operational component to monitor the occurrence of new daily, monthly, and all-time records for temperature, precipitation, and snowfall as they occur. Parallel development of a North American gridded database of daily temperature and precipitation supports these activities and will soon provide for the analysis of extremes on a regional, country, and continental-scale basis. This presentation will include an overview of the NACEM system and its products, the supporting database, observed changes in climate extremes, and future plans for the system.
A41A-08
GHCN Daily: A Global Dataset for Climate Extremes Research
The Global Historical Climatology Network (GHCN) Daily dataset is designed to facilitate climate extremes research on the global scale. The dataset contains daily temperature and precipitation time series for over 15,000 stations worldwide, with about 10,000 extending back to 1950 and several thousand being updated daily. Both historical and real-time GHCN data undergo a suite of two dozen rigorous quality assurance reviews, including checks for spurious changes in the mean and variance and neighbor checks that identify outliers from both a serial and a spatial perspective. The quality assured dataset is freely available from NOAA's National Climatic Data Center (NCDC). GHCN-Daily has been employed in a variety of extremes-related assessment activities. For example, the dataset is used operationally by NCDC in monitoring climate extremes in North America and in tracking large-scale changes in observed daily maximum and minimum temperature across the globe. GHCN-Daily data have also been used to compute a variety of climate change indices that quantified observed changes in climate extremes as well as projected changes (e.g., in warm spells) simulated by the NOAA's Geophysical Fluid Dynamics Laboratory Climate Model 2.1.