|December 17, 2013
1:00 PM – 2:00 PM ET
|Modeling at Fine Scales: Research to Improve Regional and Local Climate Information|
|Speakers and Topics:||John Dunne (NOAA/GFDL)
Prototyping global Earth System Models at high resolution: Representation of Eastern Boundary Currents
Julia Manginello (COLA)
Future changes in the western North Pacific tropical cyclone activity; results from Project Athena
Vasu Misra (Florida State University)
High resolution coupled ocean-atmosphere modeling over the Intra-American Seas
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Julia Manginello (COLA) — Future changes in the western North Pacific tropical cyclone activity; results from Project Athena – How tropical cyclone activity in the northwestern Pacific might change in a future climate is assessed using multi-decadal AMIP-style and time-slice simulations with the ECMWF Integrated Forecast System (IFS) at 16-km global resolution. The model reproduces many aspects of the present-day typhoon climatology and variability well, including the full intensity distribution and genesis locations, and their changes in response to El Nino and the Southern Oscillation.
The 16-km IFS projects a small change in the typhoon frequency at the end of the 21st century related to a distinct southward shift in the genesis locations. It is likely driven by the southeastward penetration of the monsoon trough/subtropical high circulation system and the southward shift in the activity of the synoptic-scale tropical disturbances in response to the strengthening of deep convective activity over the central equatorial Pacific in a future climate.
The model also projects about fifty percent increase in the power dissipation index mainly due to a significant increase in the frequency of the more intense storms, which is found to be comparable to the natural variability in the model. Based on the composite analysis of large samples of super-typhoons, both the development rate and the peak intensities of these storms increase in a future climate, which is consistent with their tendency to develop more to the south and within an environment that is thermodynamically more favorable for faster development and higher intensities and dynamically virtually unchanged. Coherent changes in the vertical structure of the super-typhoon composites show system-scale amplification of the primary and secondary circulations with the signs of contraction. Including an upward shift in the frequency of the most intense updrafts and overall stronger convection in the eyewall.
Vasu Misra (Florida State) — High resolution coupled ocean-atmosphere modeling over the Intra-American Seas — We have conducted coupled downscaled integrations over the Intra-American Seas at 15km grid resolution and compared the results with available observations and CFSR. A highlight of the talk is the substantial improvement in the ocean circulation features of the Intra-American Seas compared to CFSR. We argue that coupled regional ocean-atmosphere models offer a new paradigm for downscaling especially for coastal regions, especially when the progress in the improvement of global models is excruciatingly slow.
John Dunne (GFDL) — Prototyping global Earth System Models at high resolution: Representation of Eastern Boundary Currents — The world’s major Eastern Boundary Currents (EBC) are critically important areas for global fisheries. Computational limitations have divided past EBC modeling into two types: high resolution regional approaches that resolve the strong meso-scale structures involved, and coarse global approaches that represent the large scale context for EBCs, but only crudely resolve only the largest scales of their manifestation. These latter global studies have illustrated the complex mechanisms involved in the climate change and acidification response in these regions, with the EBC response dominated not by local adjustments but large scale reorganization of ocean circulation through remote forcing of water-mass supply pathways. While qualitatively illustrating the limitations of regional high resolution studies in long term projection, these studies lack the ability to robustly quantify change because of the inability of these models to represent the baseline meso-scale structures of EBCs. In the present work, we compare current generation coarse resolution (one degree) and a prototype next generation high resolution (1/10 degree) Earth System Models (ESMs) from NOAA’s Geophysical Fluid Dynamics Laboratory in representing the four major EBCs. We review the long-known temperature biases that the coarse models suffer in being unable to represent the timing and intensity of upwelling-favorable winds. In promising contrast, we show that the high resolution prototype is capable of representing not only the overall meso-scale structure in physical and biogeochemical fields, but also the appropriate offshore extent of temperature anomalies and other EBC characteristics. In terms of representation of large scale circulation, results were mixed, with the high resolution prototype addressing some, but not all, of the biases in the coarse resolution ESM. The ability to simulation EBCs in the global context at high resolution in global ESMs represents a fundamental milestone towards both seasonal to inter-annual ecological forecasting and long term projection of climate, ecosystem, and acidification baselines and sensitivity.