Observations and modeling of breaking waves in the lee of the Medicine Bow Mountains Jeffrey R French1, S. Haimov1, V. Grubišić2, M. Xiao3, L. Oolman1 1 University of Wyoming, Laramie, WY 2 University of Vienna, Vienna, Austria 3 Desert Research Institute, Reno, NV Supported through NASA and NSF 19 August, 2009 13th Conf. on Mesoscale Processes

NASA 06 Field Campaign Pennock Mountain Medicine Bow Peak Sheep Mountain NASA 06 campaign in the medicine bow mountain of SE Wyoming, Used UWKA and WCR to investigate orographic precipitation. 2 opportunities to collect data suitable for investigating dynamics associated with strong mountain lee waves Medicine Bow mountains: Dome shaped 19 August, 2009 13th Conf. on Mesoscale Processes

Objectives: 1. Use observations to describe the internal structure of mountain-induced breaking waves and rotors (scales, turbulent intensity, etc) Example: (2008 Mtn Met. Conf.) Wind Dir Jan26, leg 3; 200 m contours, aircraft altitude 5200m Highest terrain ~3300 m Dual Doppler provides 2D picture of wave (in the presence of sufficient scatterers), resolution from 100-300 m, depending on “stationarity” …. Jan 26 case (French et al) strong breaking wave captured during three passes over ~25 minute period. Dual Doppler analysis reveals strong turbulence with vortices being “shed” downstream of crest. Rapidly developing system, over the period of time it was observed. January 26, 2006 NASA06 Field Campaign 19 August, 2009 13th Conf. on Mesoscale Processes

Objectives: 2. Use numerical simulations to interpret observations and examine environmental conditions under which these features formed Example: (2009 ICAM) Modeling of Jan26 case (Grubisic et al), modleing reproduces temporal evolution of wave with upstream propagation of breaking wave and increase of wavelength over observation period. General characteristic of wave reproduced well by the model; mismatch in resolution, model is unable to capture “sub-rotor” features…more work to be done on this case. NRL COAMPS Model 5 Nested Domains Innermost domain Δx = 333 m 60 sigma-z levels 19 August, 2009 13th Conf. on Mesoscale Processes

Feb 05 Case: Multiple Passes over >1 hour wave transitions from turbulent, breaking(?) to laminar, trapped Lee-wave Wind Dir Pass 1 1,2,3,4: red, yellow, green, blue, Dual Doppler from pass 1 shows strong downslope flow, a primary wave crest with turbulence beneath and Downstream…looks similar to Jan26 case, but weaker. Subsequent passes (not shown) over the same region show much smoother flow, formation of a second, downstream wave crest, and weaker winds (horizontal and vertical) 19 August, 2009 13th Conf. on Mesoscale Processes

Vertical Wind (Single Doppler) Regions of stronger turbulence, weakening with time Vertical Wind (Single Doppler) t = 0 min t = 14 min t = 48 min t = 59 min 4 passes during a 1 hour period, Single, vertical Doppler show: A wave that propagates slightly between the first and second pass, then remains stationary Reasonably strong turbulence beneath and downstream of the primary wave crest (red line) during the 1st pass, weakening by the 2nd pass, and nearly laminar by 3rd and 4th passes. Magnitude of the vertical wind upstream of the first crest weakens from 1st pass to 4th pass 19 August, 2009 13th Conf. on Mesoscale Processes

LEG 1 Potential Temperature: UWKA Vertical Wind: Dual Doppler & UWKA Location of Maximum W No downstream Waves Strong Turbulence Zoomed in, so 0 point is a few km downwind of Med Bow Peak, “Hump” on right side is Sheep Mountain. Scale is such that distance between red-dashed lines corresponds to 6.5 m/s. Areas of interest are shown on the slide…. 19 August, 2009 13th Conf. on Mesoscale Processes

LEG 3 Potential Temperature: UWKA Vertical Wind: Dual Doppler & UWKA Location of first Maximum W Multiple downstream Waves Much weaker Turbulence Essentially the same as last slide, but for later penetration pointing out some of the differences…. 19 August, 2009 13th Conf. on Mesoscale Processes

Initial Modeling Effort for Feb05: 1400 1430 1500 Cross Section along mean flight path at times corresponding to first leg(1400), between 2nd and 3rd legs (1430), and last leg (1500) Black lines at 4200 and 5200 ft MSL correspond to location of flight legs Very generally: model shows wave activity weakening with time strong wave on downwind side of sheep mountain (we did not fly downwind of Sheep…no clouds….)…Interestingly, earlier periods (1300 & 1330) reveal strong single wave on downwind side of sheep mountain with vert vel at 4200 of +/- 4-5 m/s, this wave weakens by the time period shown on these plots. Upstream of Sheep, but downstream of Med Bow Peak (where UWKA was flying), earlier period shows single wave that transitions to multiple wave train by latest period. However, perturbation of pot T and vert velocities appear weaker than observations from aircraft. Wind (at all levels) appears more northerly in the model than observed…but need to look at this closer. 19 August, 2009 13th Conf. on Mesoscale Processes

Initial Modeling Effort for Feb05: Potential Temperature: Model and Observations at 1430Z Wind Speed: Model and Observations at 1430Z From Flight scientist notes: “6am takeoff was called for February 5th in order to catch a quickly moving, but poorly times snowstorm that was moving across the state.” …need to look closer at obs and forecasts across state, does initialization capture reality? Closer inspection….first the sounding comparisons, aircraft slight more stable, particularly right at the surface, upwind of Med Bow, in Saratoga valley, above inversion reasonable comparison… Windspeed & direction comparison: significantly weaker winds in the model than observed, this likely accounts for the much weaker waves produced by the model than seen in the observations…note that windspeed comparison at 1300 looks much more favorable, however, the thermodynamics agree less at that time…possible that the wind being driven by the large scale system is mis-timed in the model used for initialization (flight scientist notes that system moved in later than forecast) but the thermodynamics are more heavily influenced by the diurnal cycle (I know, I know, this is winter time, but still..) 19 August, 2009 13th Conf. on Mesoscale Processes

Initial Modeling Effort for Feb05: Potential Temperature: Model and Observations at 1430Z: Leg 3 Vertical Velocity: Model and Observations at 1430Z: Leg 3 Only showing comparison with leg 3 (not leg 1) Model never produces the vigor (or character of obs from leg 1….) Leg 3 model catches something similar, but much weaker. Location is in correct place, magnitude is way too small. Evolution over next ~1/2 hour looks OK, but evolution over previous half hour is not so good….. 19 August, 2009 13th Conf. on Mesoscale Processes

13th Conf. on Mesoscale Processes Need to complete the summary….. 19 August, 2009 13th Conf. on Mesoscale Processes