The objective of this research is to further clarify the effects of low-level upstream moisture on the amplitude of gravity waves generated by complex terrain when actual cloud formation processes are considered. A particular focus is the net result of two competing processes which will act to strengthen or weaken the wave activity. The method to be used begins with gathering a verification dataset of the upstream cloud structure by using a stereo photogrammetry system during the upcoming DEEPWAVE experiment. These cloud observations will be combined with upper tropospheric gravity wave data obtained by NCAR's High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) and, ideally, upstream wind profiler and radiosonde profiles collected by the Integrated Sounding System (ISS), which have already been requested as part of DEEPWAVE. The observed events will then be studied using numerical simulations in an attempt to identify conditions leading to three scenarios: 1) amplification of wave activity relative to a dry event, 2) weakening of wave activity relative to a dry event, and 3) no change in amplitude due to offsetting of the two factors.
Intellectual Merit : When the special problem of moisture effects on mountain wave activity has been examined by investigators, the focus has been on how the presence of water vapor and latent heat release modifies the air's static stability. However, separate idealized modeling studies of flow blocking show that the actual microphysical processes involved in cloud condensation can result in different behavior than that predicted from pure thermodynamics. The only way to truly know that these effects occur in the real atmosphere is to observe them, after which numerical simulations which closely match the observed behavior can be used to explain the underlying physics. Thus, the research proposed here will allow for a more complete explanation of the effects of moisture on mountain wave activity, which is part of a larger problem involving describing this activity when all possible factors (e.g. boundary layer effects) are considered.
Broader Impacts : The numerous impacts of deep, vertically propagating mountain waves are well covered by the motivation for the DEEPWAVE experiment itself. These include aviation turbulence due to breaking waves, the effect of mountain wave drag on general climate modeling, and the destruction of ozone through formation of polar stratospheric clouds. As with any human impact, there will be a desire to predict these effects and the underlying wave activity which is done with a combination of numerical modeling and subjective forecaster judgment, both of which will be improved by this research. Between the cloud photogrammetry, upstream sounding profiles, and wave information collected by HIAPER, a complete verification dataset exists for testing numerical model output with observations. Obvious areas to look for improvement would be in the microphysics parameterization, which can be matched against the cloud observations. Additionally, documenting the resulting wave activity for different large scale synoptic patterns and moisture amounts will aid human forecasters in anticipating events based on routinely available observations, such as satellite. Since this research is being performed out of an undergraduate meteorology program, there will also be excellent educational opportunities for students at an early stage in their careers. While one student will participate in the actual field campaign itself, along with the planning and subsequent analysis, the datasets collected can be easily incorporated into classroom material (especially cloud physics and wave dynamics), emphasizing the real-world applications of the more theoretical topics.
