The Doug Lilly Symposium


The application of WRF-Climate in the East Africa: the customization of buffer zones

Xuejin Zhang, North Carolina State Univ., Raleigh, NC; and L. Xie, F. H. M. Semazzi, and X. Z. Liang

As the external forcing to drive regional climate model, lateral boundary conditions can significantly affect the successful modeling of regional climate. One should consider two factors of treating the lateral boundary condition. One is the treatment of buffer zones (Liang, et al. 2001). The other is the uncertainty of the driving datasets (e.g. Santer, et al. 1999). The global reanalyses such as ERA40 and NCEP/NCAR reanalysis are usually used as the driving datasets of the lateral boundary conditions for regional climate modeling. Due to heterogeneity of the observations in space and time and the deficiencies of the assimilation system itself (e.g. Kalnay et al., 1996; Simmons and Gibson, 2000; Trenberth et al.,2001; Santer et al., 2004), the reanalyses have the systematic bias in particular regions. Therefore, the locations of the buffer zones have significant effects on the regional climate simulation. On the other hand, regional climate model is integrated more than 1 month (usually 1-4 months) so the Low Frequency Oscillation (LFO) and teleconnection pattern of the general circulation must also be considered in the buffer zones. The long-term temporal and spatial variations of the general circulation can propagate into the internal simulation region through buffer zones. This study presents these issues related to the customization of buffer zones of the regional climate simulation. First, data uncertainty always affects the regional climate simulation. The data uncertainty results from the assimilation system fed by inhomogeneous observation and assimilation system itself. Through the correlation analysis of ERA40 and NCEP/NCAR reanalysis, the uncertainty areas are identified around the simulation region of the East Africa. The different configurations of the buffer zones of the lateral boundary indicate that the large uncertain areas should be avoided to eliminate the systematic bias. Second, the integration time of regional climate model system (1-4 months) is significantly different from numerical weather prediction (3-7 days). Therefore, beside the planetary and synoptic systems, much larger temporal and spatial scale phenomena such as LFO and teleconnection systems can also influence the regional climate. In order to penetrate through the buffer zones, the variation of these systems should be included in the buffer zones. The related LFO and teleconnection pattern of the region are identified by the data analysis. Numerical experiments are also performed to indicate the effects of the LFO and teleconnection patterns. Our results indicate the effective buffer zones can improve the regional climate simulation. The customization of buffer zone supported by physical considerations can optimize the buffer zones and contribute to improvement of the regional climate modeling.

Poster Session 1, Doug Lilly Symposium Posters
Thursday, 2 February 2006, 9:45 AM-11:00 AM, Exhibit Hall A2

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