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Toward an Earth system modelDeveloping numerical models and making them available to the scientific community is at the heart of ESSL's research and service to the community. Leading the way are the Community Climate System Model (CCSM) and the Weather Research and Forecasting Model (WRF). CCSM is a coupled model combining representations of the atmosphere, ocean, land, and sea ice. WRF is a next-generation mesoscale numerical weather prediction system designed to serve both operational forecasting and atmospheric research needs. There is strong community participation both in developing the models and in using them. Additionally, ESSL continues to develop and use together with the community to a lesser extent a variety of other models within ESSL. This combined model development will contribute to the creation of a comprehensive Earth System Model , a top priority for ESSL and a task that will likely be undertaken in collaboration with CISL. This system will be developed around the interactions of the Earth's physical, chemical and biogeophysical systems with future inclusion of human and societal elements. Described below are ESSL's accomplishments and projects related to community models, research models and the creation of an Earth system model , with NCAR highlights on CCSM and the NCAR participation to the IPCC campaign, and on the CGD-MMM collaboration on Nested Regional Climate modeling which, for relatively short timescales, will allow for a direct input to societal and economical matters. Nested regional climate modeling [Highlight] - MMM/CGD Nested regional climate modelingMesoscale processes can have a major impact on large-scale circulations. Yet climate models do not adequately represent this upscale influence of mesoscale processes. This major limitation to improved predictions of the physical climate system has been recognized by the international community through the establishment of The Observing system Research and Predictability Experiment (THORPEX). In a complimentary manner, NCAR is addressing this challenge by
The successful completion of the NRCM will enable us to address—for the first time—the full implications of the effect of the local organization of clouds on regional and global climate, the impact of local wind circulations at boundaries of the major continents on the oceanic circulation, and the manner in which human activities are directly changing the world's weather and climate. While there is a wide range of upscale interactions to be considered, the most critical is the manner in which moist convection and its associated mesoscale organization influences larger-scale circulations. Current parameterization schemes in climate models do not adequately handle the mesoscale organization of convection, which is a critical missing link in the scale-interaction process. Moreover, these models tend to initiate convection prematurely, and too frequently, leading to a model atmosphere that is too stable and therefore less favorable for development of large-scale disturbances. The near-term goals of the NRCM project are to improve our understanding and ability to simulate the complex, multiscale interactions intrinsic to atmospheric and oceanic fluid motions. The accurate representation of these scale interactions is critical to both climate projections and weather predictions, and they are likely key to resolving some of the longest standing biases in climate model simulations. A particular emphasis is being placed on:
In FY2006, with the availability of significant computing resources made available by the NCAR Directorate, MMM and CGD scientists have performed a set of NRCM simulations with the Advanced Research WRF (ARW). The first stage involved converting the ARW into a tropical channel model with prescribed SST forcing, prescribed boundary conditions on the north and south boundaries, periodic boundary condition on the east and west boundaries, and high-resolution internal, two-way interactive, nested grids. This tropical channel version of WRF was run with meridional boundary conditions provided by the NCEP-NCAR reanalysis and an internal, two-way interactive grid over the maritime continent at 4-km resolution. Complementary runs were made with the CAM to enable direct comparisons. In conjunction, a series of prescribed atmosphere, high-resolution, (one-way) nested ocean model experiments have been conducted in the eastern Pacific Ocean with the goal of improving the poor performance of climate models in these regions, and also as a platform to ultimately include high trophic level marine ecosystem models into CCSM. The experiments conducted during the initial phase included:
To date, only a preliminary analysis of the model runs has been possible due to lack of resources. But these analyses have indicated both positive and negative outcomes. On the positive side, the tropical ARW has improved the resolution and propagation of tropical modes (at a level similar to that of the NCEP reanalysis), including easterly waves, Kelvin waves and the Madden-Julien Oscillation. It also has proven to be able to simulate seasonal tropical cyclone statistics with an accuracy exceeding experiments by other centers. On the negative side, the simulation generally over-estimated rainfall, and the prescribed boundary conditions created completely unrealistic rain totals in the southern Indian Ocean. Keeping the standard ARW top at 50 mb also created considerable problems in the upper stratosphere with the development of unrealistic thermal and wind fields. Future plans include analyzing the initial data, continuing experiments using the NASA Columbia computer for another six years of simulations (2000 – 2005), taking the next critical step of completing our goals of embedding ARW into CAM to undertake both current and future climate simulations, purchasing sufficient disk space to process and store (a subset of) the data locally, thereby facilitating easier access by interested NCAR and university scientists, and providing support for our university and laboratory collaborations. The NRCM project has been built on strong collaborations from the outset within CGD and MMM, who have worked closely on all aspects of the development, together with Dr. Ruby Leung's group at Pacific Northwest National Laboratory (PNL). As the analysis is commencing, several university collaborations are also developing. For example, Peter Webster at Georgia Tech has provided a student for full time work at NCAR on the tropical modes and tropical cyclone analysis, and he and Greg Holland have submitted a proposal to NSF to expand this activity. MMM and CGD have submitted a SCIDAC proposal in conjunction with scientists from several laboratories and universities. Jim McWilliams (UCLA), Zach Powell (UC Berkeley), Enrique Curchister (Rutgers), Dale Haidvogel (Rutgers), and Kate Hedstrom (U. Alaska) have visited NCAR in the past six months, and all are working on the nested ocean modeling, which is being made possible through the support and time dedicated to the project by Don Stark (NCAR, ESMF). Interest in this aspect is now coming from the National Marine Fisheries Service. Scientists at other US universities and from Korea, India, China and Taiwan have also expressed keen interest in being involved in various facets of the NRCM initiative. NCAR plans that the NRCM will eventually be provided and maintained as a community resource for use by all the academic, government, and private sector communities. The NRCM project is funded by NSF and supported by the NCAR Directorate, ESSL Directorate, and MMM and CGD divisions. Intraseasonal/tropical climate vaiability
Understanding and successfully predicting intra-seasonal tropical climate variability is a research priority for the international community as well as for ESSL. The fact that most global models have difficulty in generating and maintaining the Madden-Julian Oscillation (MJO), a prime example of intraseasonal variability, is attributed to incomplete convective parameterizations. Yet when suitably tuned parameterizations result in improved MJOs, these improvements are not necessarily robust. This suggests that key physics may be missing from contemporary convective parameterizations and that new approaches are required. The search for such “missing physics” centers on the role of organized precipitating convective systems (~ 10-km to 1000-km scales) in large-scale tropical circulations, while the new approach involves cloud-system-resolving models. These models began to be seriously exploited for weather-climate research about a decade ago, and have since progressed to global-scale computational domains as a direct result of progressive advancements in computing. The specific concept being investigated in MMM is that the upscale effects of convective organization are fundamental building blocks of the MJO. This hypothesis is examined from a broad perspective using theoretical-dynamical models, cloud-system-resolving models, super-parameterization, and the analyses of global models and observations. Recent accomplishments show: i) super-parameterization embedded in the Community Atmospheric Model (CAM) over the tropical western Pacific produces more realistic variability than contemporary parameterization with organized convection being the main contributor; ii) systematic errors in thermodynamic and momentum fields are self-similar for mesoscale (convective systems) and synoptic-scale (superclusters), suggesting fundamental scale-invariance; iii) a principle for interlocking organized mesoscale dynamics with large-scale Rossby-gyre dynamics is based on a formal mapping between the respective equations and dimensionless quantities; iv) convective momentum transport generates MJO-like systems and equatorial atmospheric super-rotation through organized upscale momentum transport reinforcing horizontally convergent flow due to planetary-scale mean heating (see figure); and v) a tropical channel model based on WRF displays strong intraseasonal variability. Future plans are to quantify the role of convective organization in the MJO by: i) dynamical and numerical modeling; ii) designing new mesoscale parameterizations for climate models; iii) multi-scale simulation of natural precipitating systems observed by TRMM/CloudSat; and iv) analysis of multi-scale convective organization in the aforementioned tropical channel model. Sponsors of this work include NSF, NSF/CLIVAR and NASA. Climate and tropical cyclones
NCAR scientists have examined the historical record of tropical cyclones in the North Atlantic for long-period variability and trends in frequency for all categories of named storms. The findings show that the past century has seen three relatively stable regimes separated by sharp upward transitions: Each regime has seen 50% more cyclones and hurricanes than the previous one and is associated with a distinct change in eastern Atlantic sea surface temperatures (SSTs). Thus there has been a substantial, 100-year trend leading to related increases of over 0.7 o C in SST and over 100% in tropical cyclone and hurricane numbers (see figure). The compelling conclusion is that the overall trend in SSTs and tropical cyclone and hurricane numbers is substantially influenced by greenhouse warming. Superimposed on the evolving tropical cyclone and hurricane climatology is a completely independent oscillation in the proportion of major to minor hurricanes. The period of enhanced major hurricane activity during 1945-1964 arose entirely from this oscillation. While there is no trend in the proportion of major hurricanes, the increasing number of cyclones has lead to a distinct trend in the absolute number of major hurricanes. Future plans include extending this work to other ocean basins. NCAR scientists will also utilize the new NCAR Nested Regional Climate Model (NRCM) to examine the environmental changes associated with these observed trends and variations of tropical cyclones. The NRCM is being coupled into the NCAR Community Atmospheric Model (CAM) to enable projections of future trends in tropical-cyclone characteristics. This work is being carried out with the support of NSF. |
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