Climate Diagnostics Center

Recent Highlights

CDC scientists provide regular input to the production of the U.S. Drought Monitor. They produce experimental seasonal forecasts every month based on tropical ocean conditions, and have created a web page to display forecasts. On the state level, they regularly provide input to and make briefings at meetings of the Colorado Water Availability Task Force and to other stakeholders on the current and projected evolution of ENSO-related anomalies and their implications for the southwestern U.S. Some experimental CDC forecasts are now being used by regional wildfire managers.

CDC scientists recently discovered an emerging long-term trend toward an increasing year-to-year variance (decreasing reliability) of streamflow across the major river basins in western North America: Fraser, Columbia, Sacramento-San Joaquin, and Upper Colorado. They also demonstrated that a concurrent increase in the incidence of synchronous flows (simultaneous high or low flows across all four river basins) has resulted in expansive water resources stress. The observed trends are associated with trends in the wintertime atmospheric circulation and ocean temperatures, raising new questions on the detection, attribution, and projection of regional hydrologic climate change.

CDC continues to participate strongly in the OGP-funded regional assessment on the effects of climate variability on water resources in the Interior West ("Western Water Assessment," or WWA). CDC scientists held frequent interactions with other federal and state agencies such as the Department of the Interior, including the Bureau of Reclamation and the Fish and Wildlife Service, and other user groups, such as the Denver Water Board, Colorado River Water Conservation District, and Colorado Drought Task Force. An important objective of this research is to learn how to better incorporate climate information and forecasts into water resource decisions in this highly water-sensitive region.

CDC also continued its strong tradition of public outreach and service to the broader scientific community. CDC staff gave numerous media interviews and specialized climate briefings, and developed new web pages explaining basic and applied CDC climate research in laymen's terms. This web site also contains links to many experimental and applied climate products developed at the Center.

Climate Diagnostics Center Accomplishments FY 2009

Publications

In 2008-2009, CDC published 27 peer-reviewed papers on topics that included:

Reconciling non-Gaussian climate statistics with linear climate system dynamics
A global view of non-Gaussian sea-surface temperature (SST) variability
The impact of rapid surface wind variability on thermal air-sea coupling
Oceanic influences on recent continental warming
Forcing of tropical ocean variability from the North Pacific through oceanic pathways
Representation of El Niño-Southern Oscillation (ENSO) in the United Nation’s Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) climate models
Evaluating the simulation of clouds, precipitation, and radiation in climate models
Sensitivity of ENSO period in climate models to the mean pycnocline structure
Tropical vs. stratospheric influences on short-term extratropical climate variations
Characteristics of North American summertime rainfall with emphasis on the monsoon
Origin of convectively coupled atmospheric Kelvin waves over South America

Data and Forecast Products

Additionally, CDC continued the development of several observational and atmospheric circulation datasets and forecast products, and provided scientific input to international programs, including:

Providing leadership in the international Global Climate Observing System Surface Pressure Working Group, to promote the development of long-term, high-quality surface pressure datasets
Completing production of version 1 of a global atmospheric circulation dataset for 1908-1958, using only daily surface pressure observations and an ensemble Kalmanfilter based data assimilation system, and making the dataset widely available through a web interface. Read More
Starting production of version 2 of the global atmospheric circulation dataset for 1891-2008, using a longer and improved surface pressure database, and an improved model for assimilating those data. The improved model includes better specifications of time-varying CO2 and aerosol radiative forcings over the assimilation period. This effort will extend our ability to quantify 20th century climate variability, provide uncertainty estimates for climate change detection, and aid attribution efforts to inform climate policy decisions.
Developing and releasing a new experimental forecast product (jointly with NOAA ESRL’s Physical Sciences Division) for subseasonal tropical forecasts based on a coupled linear inverse model of weekly tropical SSTs and outgoing longwave radiation variations. Read More

Discoveries

CDC researchers have recently discovered some surprising aspects of atmospheric and oceanic variations, with important implications for climate modeling and prediction.
For instance, two recent studies provided evidence of striking deviations from “normality” in the observed statistics of daily SSTs and of the vorticity of daily wind variations at the 300 hpa jet stream level, as shown in the figure above for the Skewness (S) and Kurtosis (K), which are both identically zero for “normally” distributed quantities.

There are several remarkable features to note in the figure below:

the patterns of S and K are highly geographically coherent in both the atmosphere and the ocean,
large magnitudes of S tend to be associated with large values of K, and
this K-S relationship is a remarkably simple parabolic inequality, K>1.5 S2, as evident in the scatter plots of K versus S in the left panels.

We have shown that this K-S relationship is a simple consequence of stochastically perturbed linear dynamics and physics. The precise values of S and K, however, depend sensitively on the extent to which the amplitude of the stochastic noise is independent of the system state or depends linearly on it. The magnitudes, geographical structures, and interrelationships of K and S evident in this figure have critical implications for climate models and their ability to represent the statistics of extreme and high-impact weather events. This is because accurate representations of K and S are necessary for accurately representing the tails of probability density functions, and therefore the likelihoods of extreme values.

Skewness S and Kurtosis K of the vorticity of daily upper tropospheric winds near the jet stream level (300 hpa), derived from the NCEP/NCAR atmospheric reanalysis dataset (upper panels), and the same statistics for daily sea-surface temperature (SST) variations, derived from a 20-yr high-resolution SST dataset (lower panels). Positive values of S and K are indicated in red and negative values in blue. For added clarity, the fields in the upper panels are also contoured at intervals of 0.4, starting at 0.2. The S and K values from the maps are displayed in the left panels in the form of scatterplots. Note the strong tendency for a parabolic K-S relationship. (Adapted from Sardeshmukh and Sura 2009 and Sura and Sardeshmukh 2008)

Cooperative Institute for Research in Environmental Sciences

Recent Highlights

Climate Diagnostics Center Accomplishments FY 2009

Publications

Data and Forecast Products

Discoveries