Climate Research and Impacts

Research focused upon understanding oceanic and atmospheric processes associated with global and regional climate change on various temporal scales and the impacts of climate variability and change. Activities under this theme include research to determine effective regional adaptation strategies, and developing and studying new climate information products and tools appropriate for evolving user needs, particularly in the Southeast United States and the Caribbean.”

There are two representative projects below:

Representative Projects


Intra-Americas Studies of Climate Processes (IASCLIP)

D.B. Enfield (RSMAS/CIMAS); C. Wang (NOAA/AOML)
 

Long Term Research Objectives and Strategy to Achieve Theme:

Objectives: To improve our understanding of and ability to predict the summer climate in the Intra- Americas Sea and surrounding land regions.

Strategy: Improve in-situ monitoring and model predictions within the IAS region and facilitate climate forecast outreach for climate applications in the IAS region.

 

Based on recent research indicating that the Western Hemisphere warm pool (WHWP) provides the climate memory in the IAS region, developing in the spring and influencing the atmosphere in the summer, an international research program has been developed to achieve the above objectives, as part of the International CLIVAR program on American monsoons (VAMOS). The Intra-American Studies of Climate Processes (IASCLIP) began in 2009 and continues through 2014. At the 11th Annual VAMOS Panel Meeting in May 2008, David Enfield was named as chair of the IASCLIP Science Steering Committee.

The potential impact of IASCLIP is illustrated by the attached figures. Figure 1 shows the large difference in warm pool size between the five largest and five smallest warm pools since 1950, 27 approximately a factor of three. Research indicates a strong relationship between warm pool size and extreme climate events, in particular, Atlantic hurricane activity, and the influence on floods, droughts and tornados east of the Rocky Mountains, controlled by the flow of moisture into the United States across the gulf coast. Figure 2 shows the climate scenario in the Western Hemisphere tropics during spring 2010, illustrating the development of a very large WHWP (warm tropical North Atlantic) in response to a prolonged El Niño in the Pacific and a persistent (six months) negative North Atlantic Oscillation (NAO). The Hovmuller of SSTA illustrates how the tropical Atlantic has gone from being somewhat cool in 2009 to being extremely warm in 2010, each in response to distinct atmospheric forcings in the winter-spring season. The mantra of IASCLIP is that by emulating this and other warm pool development mechanisms (e.g., ENSO), improved numerical models can produce useful summer climate forecasts.

Orchestrating the launch of IASCLIP. This has involved (1) working with other IASCLIP scientists to organize the efforts of several working groups; (2) participating in trips to several Caribbean countries to organize collaborative activities, and now, (3) preparing to address the VAMOS Panel meeting (July 2010) regarding the progress and future plans for IASCLIP.

Figure 1. (a) Difference between the largest and smallest wrm pools since 1950 (heavy contour = 28.5°C). (b) Time series index of WHWP size (% of climatological July value).

Figure 2. The evolution of the Atlantic warm pool (AWP) in spring 2010 is an excellent illustration of the importance of winter-spring climate patterns to AWP growth. There is a warming in the tropical North Atlantic in response to a prolonged El Niño in the Pacific and a persistent (six months) negative North Atlantic Oscillation (NAO). These are associated with a weaker-than-normal NASH and easterly low-level winds over the TNA (lower left), allowing the tropical North Atlantic to warm faster than normal.

 

Understanding Discrepancies between Satellite-Observed and GCM-Simulated Precipitation Change in Response to Surface Warming

B.J. Soden (UM/RSMAS); G. Vecchi (NOAA/GFDL)
 

Long Term Research Objectives & Strategy to Achieve Them:

Objectives: Understand the cause of discrepancies between observed and model-simulated precipitation variability over the tropical oceans.
Strategy: Compare satellite observations with empirical analyses and climate model simulations to evaluate the veracity and cause of decadal variations in the tropical precipitation.

 

Future substantial changes in the global water cycle are an expected consequence of a warming climate; this is based upon understanding of the governing physical processes and projections made by sophisticated models of the Earth's climate system. Monitoring changes in tropical precipitation is a vital step toward building confidence in regional and large-scale climate predictions and the associated impacts on society.

A number of robust large-scale responses of the hydrological cycle have been identified in models, relating primarily to increases in low-level moisture with temperature, a consequence of the Clausius-Clapeyron equation. Improving confidence in climate projections demands the use of observations, sampling the many aspects of the global energy and water cycles, to evaluate the relevant processes simulated by models. It is important to establish causes of disagreement, for example relating to observing system deficiencies or inadequate representation of forcing and feedback processes in models. There is observational evidence of increased tropical monthly-average moisture and precipitation and an amplification of extreme precipitation events in response to atmospheric as well as a contrasting precipitation response over wet and dry regions of the tropics. While observed precipitation responses appear larger than those simulated by models it is unclear whether this relates to model deficiency, inadequacy in the observing system or is a statistical artifact of the relatively short satellite record.

In Allan et al. (Envir. Res. Lett., 5, doi: 10.1088/1748-9326/5/2/025205, 2010) and Chung et al. (Geophys. Res. Lett., 37, L02702, doi:10.1029/2009GL041889, 2010) we examine current changes in tropical precipitation and its extremes, and the radiative feedbacks which govern them. In particular we addressed the questions: (1) What are current trends in tropical mean precipitation? (2) Are the wet regions becoming wetter at the expense of the dry regions? (3) Is there an intensification in extreme precipitation with warming in models and observations over the period 1979-2008? (4) How consistent are observed and model-simulated rates of radiative feedbacks?

Current changes in tropical precipitation from satellite data and climate models were assessed. Increased precipitation in moist, ascending regions and reductions in drier descending branches of the large-scale circulation, previously identified, were sensitive to the reanalysis products used to define these regions. To avoid homogeneity issues with reanalysis fields, wet and dry regions of the tropics were defined as the highest 30% and lowest 70% of monthly precipitation values. Observed tropical ocean trends in the wet regime (1.8%/decade) and the dry regions (-2.6%/decade) for the Global Precipitation Climatology Project (GPCP) over the period including Special Sensor Microwave Imager (SSM/I) data (1988-2008) were of smaller magnitude than when including the entire time-series (1979-2008) and in closer agreement with model simulations than previous comparisons. Analyzing changes in extreme precipitation using daily data within the wet regions we found that SSM/I observations indicate an increased frequency of the heaviest 0.2% of events of 49 approximately 60% per K warming. This is at the upper limit of the model simulations which display a substantial range in responses. However, we find that the radiative feedback processes which govern variations in clear-sky longwave damping are highly consistent between bservations and models.