An investigation of boundary-forcing sensitivities in a regional climate model

The sensitivity of a regional climate model to lateral, upper, and lower dy namical forcing is evaluated for a pan-Arctic domain. The experiments focus on a month-long case study of May 1990, but the results are shown to be ex tendable to January and July 1990. Although the control simulation is found to adequately represent major tropospheric circulation features, a large n egative geopotential height bias of up to 700 m is found at the upper level s of the model. Experiments find these biases are remedied through the repl acement of a reflective rigid lid upper boundary condition with a local wav e-absorbing layer. Geopotential height biases are reduced to a maximum unde restimation of only 50 m at the upper boundary. Substantial improvement is also found in the simulated temperature and zonal wind profiles, transient heat and momentum fluxes, and stationary eddies as seen through the Eliasse n-Palm flux divergence. With this wave-absorbing upper boundary condition i n place, additional improvement is found using a gravity wave drag paramete rization appropriate for this domain's 100 km horizontal resolution. Additi onal sensitivity to lateral forcing is examined, and the relative role of t he upper boundary condition to skillful simulations within the Arctic basin domain is discussed.