Xiaoqian (Michael) Zhang
Research page
I have been working on a number of projects based on understanding and predicting circulation over the Texas-Louisiana continental shelf. The Texas-Louisiana shelf is a broad shelf with strong buoyancy forcing from the Mississippi and Atchafalaya rivers. Seasonal wind patterns cause the fresh water from these rivers to pool up south of Louisiana in the summertime, and to flow downcoast along the Texas coast during the rest of the year.
We run a nowcast/forecast model of wind-driven circulation over the Texas-Louisiana continental shelf for oil spill trajectory modeling. We use predicted wind fields (the NCEP ETA model) to drive a circulation. This work is funded by the Texas General Land Office.
Seasonal hypoxia forms in near-bottom waters over the Texas-Louisiana shelf in late summer. My research involves examining the influence of physics on the formation, maintenance and destruction of seasonal hypoxia. I have demonstrated that there are different regions along the shelf in which the processes that form hypoxia are distinct. This work is funded by the National Oceanic and Atmospheric Administration.
Near the vicinity of 30° latitude, the coincidence of the period of sea breeze and inertial period of the ocean leads to a maximum near-inertial ocean response to sea breeze. This produces a propagating inertial internal (Poincare) wave response that transfers energy laterally away from the coast and provides significant vertical mixing. We investigate the latitudinal dependence of this wave propagation and its associated vertical mixing primarily using a nonlinear numerical ocean model. Three-dimensional idealized simulations show that the coastal oceanic response to sea breeze is trapped poleward of 30° latitude, however, it can propagate offshore as Poincare waves equatorward of 30° latitude. Near 30° latitude, the maximum oceanic response to sea breeze moves offshore slowly because of the near-zero group speed of Poincare waves at this latitude. The lateral energy flux convergence plus the energy input from the wind is maximum near the critical latitude, leading to increased local dissipation by vertical mixing. This local dissipation is greatly reduced at other latitudes. We consider the implications of these results for the Gulf of Mexico (GOM) at ~30°N. Simulations with realistic bathymetry of the GOM confirm that a basin-wide ocean response to coastal sea breeze forcing is established in form of Poincare waves. Enhanced vertical mixing by sea breeze is shown on the model northern shelf, consistent with observations on the Texas-Louisiana Shelf.
ROMS is an open-source, community ocean model. ROMS uses a horizontal, curvilinear C-grid and a stretched vertical coordinate. In addition to the core hydrodynamic engine, ROMS has many additional packages for calculating biogeochemical processes, sediment transport. I have been using ROMS for nearly a decade, and have contributed to the code base by adding riverine fresh-water fluxes.
Python is a high-level scripting language, similar to perl or matlab. Python has powerful numerical computing packages, primarily based on numpy/scipy that make it ideal for scientific computation and analysis. For visualization, I use the matplotlib package. In many ways, Python is as simple to learn and as powerful MATLAB, both in terms of computational ability and speed as well as visualization. However, Python is based on a more powerful, object-oriented programing language. For more information, see my Python page.
I maintain a number of high-performance cluster computers. These machines are either Intel or AMD processors, and are connected with Infiniband. I have purchased my most recent clusters from Advanced HPC. Links to the ganglia pages for each cluster:
Texas A&M University
Department of Oceanography