NCEP's Two-way-Interactive-Moving-Nest NMM-WRF modeling system for Hurricane Forecasting

At NCEP, a preliminary version of the moving, two way interactive nested grid NMM-WRF modeling system is now being evaluated and tested for the numerical hurricane predictions. Based on horizontal mesh refinement technique, this nesting capability commonly referred to as “telescopic mesh” currently supports one and two way interactions between a lower-resolution domain and one or more higher-resolution nests and automatic grid motion of the higher-resolution nest. The dynamical system of equations and the numerical techniques are described in Janjic et al, 2001 for a uniform domain and is now extended onto the telescopic, nested domains. All parent-to-nested domain interpolations are done on a rotated lat-lon, E-grid with the reference lat-lon located at the center of the parent domain. Consequently the nested domain can be freely moved anywhere within the grid points of the parent domain, yet the nested domain lat-lon lines will coincide with the lat-lon lines of the parent domain at integral parent-to-nest ratio. This coincidence of grid points between the parent and nested domain eliminates the need for more complex, generalized remapping calculations in the WRF Advanced Software Framework (Michalakes, 2005) and is expected to aid better distributed memory performance, and portability of the modeling system. High-resolution topography and land-sea mask are redefined over the nested domain using the wrfsi dataset. To be consistent with the NMM model numerics, quasi-hydrostatic mass balancing is carried out after introducing the high resolution topography. Cubic spline technique is used to interpolate data back and forth from standard pressure surfaces on to the hybrid surfaces. The grid motion algorithm is based on the variations in dynamic pressure. The so called “stagnation point” was chosen to be the center of the storm (Gopalakrishnan et al 2002). For the two-way interactive technique, grid volume averaged mass, momentum and scalar fields from the high resolution nest is weighed and fed-back into the parent domain.Numerical evaluation of the nest motion technique yields satisfactory performance. Testing of idealized and real cases of Hurricanes of the past seasons will be presented.

References:

(1) S. G. Gopalakrishnan, David P. Bacon, Nash'at N. Ahmad, Zafer Boybeyi, Thomas J. Dunn, Mary S. Hall, Yi Jin, Pius C. S. Lee, Douglas E. Mays, Rangarao V. Madala, Ananthakrishna Sarma, Mark D. Turner and Timothy R. Wait. 2002: An Operational Multiscale Hurricane Forecasting System. Monthly Weather Review: Vol. 130, No. 7, pp. 1830–1847.

(2) Z. I. Janjic, J. P. Gerrity Jr. and S. Nickovic. 2001: An Alternative Approach to Nonhydrostatic Modeling. Monthly Weather Review: Vol. 129, No. 5, pp. 1164–1178.

(3) John Michalakes WRF SOFTWARE. 6th WRF / 15th MM5 Users' Workshop, National Center for Atmospheric Research June 27-30, 2005.