In accordance with idealized theory regarding the occurrence of varying degrees of “upstream blocking”, in which an appreciable fraction of the incident flow is forced to divert around (vs. surmounting) a major mountain barrier, data from the NOAA P-3 platform are processed for two diverse events: (1) a case of profoundly blocked flow exhibiting minimal precipitation enhancement directly over the orography but with appreciable low-level convergence and echo extension upstream of the Alps during IOP8 of MAP (the Mesoscale Alpine Programme, conducted in autumn of 1990), and (2) a case of relatively unimpeded (i.e. “unblocked”) flow exhibiting significant orographic precipitation enhancement over the windward (western) slopes of the Oregon Cascades during IOP11 of IMPROVE-II (the second phase of the “Improvement of Microphysical PaRameterization through Observational Verification Experiment”), conducted during late 2002.
In both cases, the arrival of strong, moist pre-frontal flows supported the development of deep, horizontally extensive precipitation shields that in turn provided the means to illuminate large atmospheric volumes over and around a zone of sharply rising terrain. Composite analysis approaches encompassing multiple flight legs are employed in both cases to gain a spatially expansive “barrier-scale” view of mesoscale flow and precipitation patterns adjacent to (or in the case of IMPROVE, on both sides of) the mountain crestline. The execution of overlapping dual-Doppler scans as obtained via a regimented “square wave” flight pattern employed during IMPROVE-II allows evaluation of traditional upper-boundary condition assumptions via a direct quad-Doppler solution technique first employed during TOGA-COARE. This test is particularly relevant in the presence of an intense mountain-wave signature, such as that shown to extend well beyond echo top in high-resolution MM5 simulations of the IMPROVE IOP11 case. More spatially limited but temporally continuous data from other platforms (e.g., ground-based S-POL and vertically-pointing S-band measurements confined to the mountain slopes) being discussed by other IMPROVE-II PI’s making submissions to this conference serve to provide desirably comprehensive description of these events.