Flight Scientist Notes – NASA-06: 2 February, 2006
18:53-22:06 UTC (~noon-3 pm)
Crew: Thomas Drew, Bart Geerts, Larry Oolman, Perry Wechsler.
Ground instruments:
Glees: hotplate and WV-1500 (5-channel) (10 times under our track incl. one circle)
N. Platte Ranch: WV-1100 (2-channel) N41º15’36’’, W106º46’42’’ (well south of our track)
UWKA flight pattern:
We flew 3 cross legs at 14 kft, then the W part of an H (“WH”), then a sounding over SRT to 17 kft, then across at 17 kft, then the E part of the H (“EH”), then 6 cross-legs at 14 kft. Specifically, the waypoints were: LAR-14GLEE14-14GLEW14-14GLEE14-14GLEW14-9.6WHN8-8WHS8-8GLEW17-17GLEE14-10EHN9-9EHS9-9EHN9-14GLEE14-14GLEW14-14GLEE14-14GLEW14-14GLEE14-14GLEW14-circle over GLEES-14GLEE14-LAR.
definitions:
GLEE, GLEES, and GLEW are aligned along 111.5º-281.5º true
GLEE is the eastern end just east of the tree-less ridge north of Centennial (the turn took us across the little Laramie River), 16 km east of GLEES.
GLEW is 40 km W of GLEES, about 5 km east of Saratoga. We sometimes turned around before reaching GLEW, because of lack of echoes.
the flight levels are shown in kft (14 kft=4276 m MSL)
Sounding above Saratoga: 19:57-20:06 UTC (8-17 kft)
The wind direction at 14 kft generally was from a slightly northerly direction relative to the flight track: the track was 5-20º counterclockwise relative to the wind. The wind backed about 10º during the 3 hrs of flight. Winds veered with height a bit, from ~270º at 8 kft to ~300º at 17 kft. Wind speed was about 15 kts at 14 kft. Temperature was about -20ºC at 14 kft.
Weather: This is a great case for the study of isolated orographic precip development, and of aerosol modification due to this precip. Clouds formed on the upwind side as streamers over the hills, and they rapidly grew into cumuli congesti (tops 15-16 kft) with significant liquid water at flight level, possibly in drizzle-size droplets (suggested by FFSP). The development of snow clearly took some time, as cumuli on the upwind side were mostly echo-free and equally vigorous cumuli closer to the crest produced WCR echoes up to 20 dBZ. On the lee side the clouds lost their definition and collapsed, but WCR echoes continued well after the clouds had dissipated, mostly in a shallow layer 1000-500 m above the terrain, thinning towards the east. Cloud tops were deepest above the crest or just upwind of the crest, and for some time (during the last 6 cross legs) a cirrus layer was present at about 17 kft above the peak only, and some cumuli reached this cirrus.
Earlier in the day (mainly 16-18 Z, 3-1 hr before take-off) the Snowy Range had been blanketed by steady light snow from a deep stratiform layer (cold satellite IR and echoes visible from Cheyenne) that had formed some 6 hrs earlier on the cold side of a strong jet (it was not predicted by MM5 or ETA). That band was moving off at the time of arrival. The first 3 flight legs saw this deeper layer of cloud well above flight level. This layer produced a weak echo up to 1200 m above flt level; the sun was readily visible thru it. It was thicker to the southeast, and it drifted off in that direction. The layer clearly seeded the well-defined clouds below, and the echo was continuous. It extended over the SRT valley, esp. the southern end, but echoes did not reach the ground there. The good isolated orographic cumuli only developed later, while doing the H legs.
The H pattern legs suggest that the wind in the upwind valley is complex, possibly channeled around the Snowy Range and into the gap south of Elk Mtn. Soundings had suggested a stable layer at about 10-12 kft MSL but we did not see that. Light turbulence was encountered in the cumuli, slightly stronger turbulence on the E side of the Range.
A stationary, persistent cloud band formed about 20 km north of Elk Mtn, and extended downwind, and towards the end of the flight it was deep enough to produce some snow towards the east, esp. over the Laramie Range.
Instruments: It appears that all systems worked well. Another CCN unit was used for the first time in NASA06, and apparently it performed well. Questions were raised about the FSSP. At the end of the flight, when shutting the nadir port, Perry noted that the WCR turbo was not set correctly.
Coordination with WMI Cheyenne aircraft (N234K): none (they took off at 22 UTC, about the time we landed).
WCR data: Probably the most interesting observation from the WCR was the growth of echoes during the last 6 cross-mountain legs from the upwind side to the crest. Echoes were relatively weak and shallow, max reflectivity mostly ~10 dBZ. Visible cloud contours appeared much more cumuliform than the WCR echoes. The upward + dual-downward looking configuration of the WCR was used exclusively for this flight, even on the H legs. The number of range gates recorded (150 gates or 4.5 km recorded range) was plenty.