IOP 1, 28-29 Nov 2001

IOP 1: 28-29 November 2001

Time Period of IOP

1200 UTC 28 Nov-0300 UTC 29 Nov

Overview of IOP

A very intense short wave trough formed over the Pacific Ocean and moved toward and over the Pacific Northwest during 26-27 November 2001. The trough moved into and across Oregon between 1200 UTC 28 November and 0000 UTC 29 November (Fig. 1a, Fig. 1b). The 850 mb winds were generally southwesterly as the trough approached (Fig. 2a, Fig. 2b). A surface cyclone and frontal system were present at the surface in association with this trough (Fig. 3a, Fig. 3b). The warm-frontal clouds moved over Oregon between about 0300 and 1200 UTC; and the cold-frontal clouds came through Oregon about 1200-2000. Fig. 4 shows the infrared satellite view at 1400 UTC. The Eta model and MM5 forecast precipitation moving through the area in conjunction with the cloud system (Fig. 5).

The S-Pol radar showed precipitation moving through the Oregon Cascades from 0400 UTC 28 November 2001 through 1600 UTC 29 November 2001. The warm-frontal precipitation had maximum intensity at about 1000-1100 UTC (Fig. 6) and was quite stratiform, as can be seen in the cross section along the 112 degree azimuth (Fig. 7). Above 2.0 km the particles consisted of dry snow with some wet snow and light rain below (as seen in the RHI along the 85 degree azimuth, Fig. 8). As the cold-frontal region approached the radar, the echoes had embedded convective cells (as can be seen along the 112 degree azimuth, Fig. 9). The wet snow in the melting layer became more obvious, and some graupel was embedded in the pattern (e.g. along the 85 degree azimuth at 1800 UTC, Fig. 10). As the back portion of the frontal echo approached the radar from the northwest, it exhibited elongated NW-SE wavelike rainbands (Fig. 11). The P-3 and Convair aircraft obtained taking data in the region of the S-Pol radar from about 1900 UTC 28 November until about 0100 UTC 29 November (Fig. 12). The P-3 (red track) flew a dual-Doppler pattern, while the Convair (yellow track) flew a vertical profile pattern for microphysics sampling.

After the cold front passed through Oregon, the precipitation took on a more convective character. A secondary trough went through the area between 0900 and 1400 UTC 29 November. The precipitation intensified during this time. Figure (Fig. 13) (PPI of reflectivity at 1.5) shows orographic convection to the east of the radar and the mesoscale echo associated with the secondary trough approaching from the west. The echo tops in the secondary trough were about 7-8 km and there was some evidence of graupel (Fig. 14, Fig. 15).

After 1600 UTC 29 November there were a few decaying convective cells to the east of the radar Fig. 16. From 1700-1922 UTC 29 November, the Convair flew a vertical profile for microphysical measurements over Santiam Pass in these remaining cells (Fig. 17).

The ETL S-band vertically-pointing radar showed detailed vertical and horizontal structures during the passage of the storm over Oregon. The passage of the warm front was evident as a layer of light precipitation which lowered to the surface from about 0730 to 1030 UTC 28 November 2001 (Fig. 18a, Fig. 18b). During the passage of the cold-frontal precipitation, the echo showed small-scale cells in the snow layer extending down through the melting layer as fallstreaks in reflectivity and with indications of updrafts in the cells in the radial velocity data (for example, between 1700 and 1900 UTC 28 November, Fig. 18c). During the postfrontal period the cells became shallower and less frequent (for example, 0800-1100 UTC 29 November, Fig. 18d). The echo associated with the secondary trough was more continuous again between 1200 and 1500 UTC (Fig. 18e, Fig. 18f), but much shallower than the echo associated with the primary cold front. After 1500 UTC the echoes became more scattered in the postfrontal regime (Fig. 18f).

Convair-580 Summary

UW Flight Number:

1891

Period of Flight:

1810-2329 UTC, 28 November 2001

Main Accomplishment of Flight:

Measurements in pre-frontal, frontal and postfrontal conditions across the Oregon Cascades. Landed in Eugene, Oregon

Instrument Problems:

SPEC CPI, Cambridge dew point, Rosemount pressure and PMS 1-D cloud probe.

Flight Scientist:

Peter V. Hobbs

Approximate UTC Timeline (Local time= UTC-8 hours) Activity for UW Flight 1891:

1822	Takeoff from Paine Field
1822-2015	Transit to Oregon.
2035-2048 At 43˚16.1'/124˚29.	9' (on Oregon coast SW of Santiam Pass) SW point and headed N at 12,000 ft.
2048-2053 .	NE --> SW descending
2053-2107 .	SW-NE at 19,500 ft
2109-2132	NE --> SW descending to 17,000 ft.
2134-2148	SW --> NE at 17,000 ft.
2149-3	NE --> SW descending to 14,500 ft. Picked up significant ice on descent to 14,500 ft. Circled in clear air at SW point to shed ice.
~2225-2240	SW --> NE at 17,000 ft.
2240	Return to SW with slow descent (more icing in Cu).
Land at Eugene.
2329	2330 Engines off.

UW Flight Number:

1892

Period of Flight:

0011-0129 UTC, 29 November 2001

Main Accomplishment of Flight:

Transit from Eugene, Oregon, to Paine Field, Washington. Cloud and precipitation measurements on climb out from Eugene.

Instrument Problems:

As for Flight 1891.

Flight Scientist:

Peter V. Hobbs

Approximate UTC Timeline (Local time= UTC-8 hours) Activity for UW Flight 1892:

00??	Takeoff.
0016-0031	Climb to 10,000 ft. Cloud tops ~15,000 ft.

UW Flight Number:

1893

Period of Flight:

1558-2039 UTC, 29 November 2001

Main Accomplishment of Flight:

Vertical profile from 15,000 ft down to 2,000 ft between Sweet Home and Santiam Pass, Oregon, in postfrontal conditions. Measured CCN spectra in inflow to clouds over Cascades and in outflow. Profile through small cumulus clouds over PNNL PARSL site at Sisters Airport on east side of Cascades.

Instrument Problems:

Discrepancy between FSSP-100 and PVM-100. Intermittent outages of HVPS.

Flight Scientist:

Peter V. Hobbs

Approximate UTC Timeline (Local time= UTC-8 hours) Activity for UW Flight 1893:

1606	Takeoff.
1606-1709	Transit to Sweet Home.
1709-1725	Sweet Home à Santiam à 15,000 ft à 10,500 ft. No cloud at this height.
1725-1750	Return to Sweet Home à descending to get into cloud tops, 10,000 ft à 5,000 ft à 2,000 ft.
1755-1810	CCN spectra in inflow air to clouds just west of Santiam at 2,000 ft.
1810-1830	West à Sweet Home à Santiam.
1830-1855	To PARSL site.
1857-1912	CCN spectra in outflow below cloud base near PARSL site.
1914-1922	Spiral up over Sisters Airport (PARSL site).
1922 .	Transit home

P-3 Summary

P-3 Flight Number:

011128H, IMPROVE 01

Period of Flight:

1936 UTC 28 November-0122 UTC 29 November 2001

Main Accomplishment of Flight:

Support of UW Convair operations (SW-NE transect) over S-POL & Santiam Pass in Oregon Cascades during cold-frontal passage and postfrontal conditions.

Instrument Problems:

Flight Scientist:

Nick Bond

Approximate UTC Timeline (Local time= UTC-8 hours) Activity for P-3 Flight 01:

193613 UTC (47.90024, -122.28056) .755°, 965.6 mb, 3.0 m Engine Start

194312 UTC (47.90022, -122.28049) 5.593°, 965.0 mb, 3.0 m Block Out. Taxi to 16R

195517 UTC (47.90895, -122.28560) 179.130°, 968.6 mb, 5349.0 m Takeoff

195859 UTC (47.77825, -122.42265) 260.415°, 884.1 mb, 901.0 m Cloud physics system up but with some initialization problems.

200534 UTC (47.53393, -122.76604) 181.575°, 689.7 mb, 2593.0 m Radar system up, recording on DR1. Slewable (AOC) antenna. LF at 2 RPM.

201207 UTC (47.20762, -122.95032) 205.434°, 574.3 mb, 4289.0 m Tech swapping cards on precip/cloud probes to get data into proper size range. Echo tops near 6km.

201939 UTC (46.76801, -123.12292) 181.582°, 554.9 mb, 4436.0 m PMS data looked good as we came through echo last few min; now in clear. ETA Pt A is 2047UTC. Echoes thinning out here.

203124 UTC (46.07021, -123.10075) 175.955°, 556.5 mb, 4275.0 m Crossing Columia; echoes picking up, especially east of track

204001 UTC (45.53973, -123.02272) 175.024°, 561.6 mb, 4428.0 m Descending to 7kft, requesting 6kft. Echoes not too horizontally extensive, a little spotty, shallow.

204407 UTC (45.29348, -123.01978) 183.274°, 745.8 mb, 2191.0 m Tech bringing cloud physics back online. Top of BB near 2km.

204853 UTC (45.01687, -123.03389) 180.966°, 794.4 mb, 1774.0 m At Pt A, tracking 180. On tail view (out only to 40km range), echo generally more extensive west of track, tho some stuff hanging over Cascades to east.

205138 UTC (44.86903, -123.03319) 180.763°, 792.6 mb, 1691.0 m Passing over Salem; out of echo, grnd visible thru bkn clouds. LF suggests echo picking up just beyond 100 km, some intermittent NNE-SSW banded structures beyond that, but nothing too noteworthy.

205603 UTC (44.61491, -123.03305) 180.067°, 795.4 mb, 1733.0 m Echo picking up slightly to west of track.

210014 UTC (44.37672, -123.03346) 180.964°, 795.7 mb, 1719.0 m Some orographic enhancement/echo slant suggested on LHS. Cloud & precip probe data continue to look high quality. Melting aggregates, clusters of needles.

210737 UTC (43.97016, -123.03192) 179.703°, 795.6 mb, 1640.0 m Precip picking up as we

210917 UTC (43.87938, -123.03072) 178.763°, 795.4 mb, 1651.0 m Cold-frontal type shear (w/ suggestion of head structure) between 10-20 km range on LHS; some precip enhancement, but certainly no strong NCFR signature

211025 UTC (43.81692, -123.03029) 180.692°, 795.7 mb, 1625.0 m At Pt F, turning east, climbing to 9kft.Top of solid echos 3-3.5 km; top of BL near 2 km (round numbers)

211431 UTC (43.76334, -122.62691) 88.611°, 736.9 mb, 1098.0 m At Pt G, turning to track 360.Nice fallstreaks originating near 4-5 km.

211821 UTC (44.03061, -122.56519) .182°, 736.8 mb, 1827.0 m Continued fallstreaks w/evidence of generating cells

212338 UTC (44.43035, -122.56558) 359.102°, 736.6 mb, 1867.0 m Vr data show continued suggestion of cold-frontal type shear, immediately west of our track. Still no hint of NCFR enhancement however. Bulk of steady precip appears to be ahead of cold-frontal wind transition.

212718 UTC (44.71851, -122.56601) 1.039°, 736.7 mb, 2004.0 m Echoes again on the wane; perhaps general decrease of precip intensity to north, or alt. Tendency for SW-NE cold-frontal orientation putting best echoes farther east at north end of pattern.

213056 UTC (44.99189, -122.55467) 40.073°, 725.5 mb, 2200.0 m At Pt B, turning east & climbing to 11kft

213503 UTC (45.01260, -122.11125) 115.543°, 656.1 mb, 2077.0 m At Pt C, turning to track 180. Echo coverage more extensive to east of track.

213710 UTC (44.89366, -122.08392) 181.803°, 656.6 mb, 1972.0 m Some evidence of orographic enhancement (sharp western edge to heavier precip) 5-10 km west of our track. Tech took brief MPEG movie of tail showing frontal-like shear and associated west edge of frontal and/or orographic precip enhancement.

214242 UTC (44.54816, -122.08353) 179.451°, 656.2 mb, 2152.0 m Suggestion of KH waves at echo top to west of track last few min. More gen cells on RHS 2143-44. Some perturbations on J-W liquid water 2145-46.

215055 UTC (44.07003, -122.08437) 181.335°, 656.6 mb, 1670.0 m Picking up some significant rime ice on wings, J-W reaching ~0.5 g/kg

215303 UTC (43.94911, -122.08315) 179.848°, 656.5 mb, 2403.0 m Radar down at 2148:17. Lost de-ice on Prop #2, need to climb.

215510 UTC (43.82835, -122.08342) 181.248°, 656.4 mb, 2046.0 m Radar back up & recording on DR1. Convair will be at 14.5 kft, so we are requesting 16kft. At Pt H, turning east.

215937 UTC (43.77388, -121.64743) 89.487°, 572.1 mb, 3064.0 m At I. Executing outside turn to track 360. Out of cloud. Will maintain FL 16kft

220753 UTC (44.18489, -121.61774) .023°, 537.2 mb, 3475.0 m Nice visualization of precip spillover on crest to LHS. Echo dissipates totally 10-20 km east of our track.

221729 UTC (45.00552, -121.61293) 28.210°, 542.6 mb, 3719.0 m At Pt D. More precip extending east of our track here at north end, so will proceed with last leg (east-J).

222503 UTC (44.81872, -121.13411) 180.539°, 682.9 mb, 2419.0 m Now south-bound on east-J. Still at -6.1 ^oC, so not much hope of getting rid of ice. Fairly smooth even here in lee.

223217 UTC (44.36913, -121.13553) 179.246°, 682.9 mb, 2174.0 m Some echo on this leg, but not much, principally west of track, desert in view below. Planning J-K-G.

223621 UTC (44.11808, -121.12251) 179.916°, 682.8 mb, 2040.0 m Running out of echo, 5 min from turn. Shedding some ice here at –5 ^oC. Planning 10 kft J-K. Then climb to >13kft.

224244 UTC (43.74215, -121.11388) 123.986°, 682.9 mb, 1258.0 m At Pt J. Convair preparing to land for refueling; they had major icing issues, unsure if they want to execute 2nd pattern.

225306 UTC (44.26260, -121.47310) 322.695°, 683.2 mb, 2079.0 m Plan climb to FL 130 at K. Once again nice spillover coming off crest LHS

225459 UTC (44.36508, -121.55649) 356.377°, 654.3 mb, 2370.0 m At K, spiraling up. Consulted w/ Roles; suspended recording of Spectal Width and saved to IMPR1; according to Roles this will improve radar system stability (and save tape ;) Mix of pristine crystals (needles, dendrites) and amorphous forms as we climb.

230621 UTC (44.13600, -121.88629) 233.935°, 606.1 mb, 2316.0 m LF suggests increasing postfrontal activity (NNE-SSW bands?) immediately off shore. Some discussion of sticking with today's situation (vs. A separate flight tomorrow) to do postfrontal work.

231008 UTC (44.01292, -122.12607) 234.278°, 606.0 mb, 2636.0 m Elevated "secondary BB" feature exhibits top near our FL

232200 UTC (43.73032, -122.49013) 339.262°, 724.1 mb, 1865.0 m At Pt G. Turning to track 360. Dynamic slip pressure is iced up, so winds messed up, but can be corrected post-flight.

233106 UTC (44.37158, -122.57019) 1.593°, 735.5 mb, 2025.0 m Further suggestion of echo "plumes" coming off sloped terrain features to east (RHS) of our track past few min. However, echo definitely on wane as we proceed north abeam of less impressive terrain. Temps on this leg are running 3 °C cooler than 1st iteration.

234008 UTC (45.04402, -122.55222) 34.309°, 719.1 mb, 2224.0 m At Pt B, climbing to 11kft. Minimal shallow echoes here.

234417 UTC (45.09106, -122.12123) 103.131°, 655.0 mb, 2111.0 m At Pt C, turning to track 180.

000625 UTC (43.79105, -122.03868) 163.161°, 651.1 mb, 1831.0 m At Pt H, climbing to 13 kft. Precip once again picked up toward south end of pattern abeam of higher terrain

000950 UTC (43.71880, -121.70859) 87.814°, 606.4 mb, 2634.0 m At Pt I, turning to track 360. LF continues to suggest NNE-SSW banded structures--one roughly through our present location, and another more closely tied to coastal range, perhaps additional band(s) about 100 km offshore

001656 UTC (44.26968, -121.61063) 1.643°, 606.2 mb, 2874.0 m Just went through biggest bump of day, though nothing obvious on radar.

002258 UTC (44.75838, -121.61922) 359.929°, 606.3 mb, 2829.0 m Still has been suggestion of nice sloped (hydraulic jump?) type flow transition coming off crest on LHS

Will ferry Paine via Olympia at FL 140

002620 UTC (45.03315, -121.62498) 358.606°, 604.8 mb, 2752.0 m At Pt. D. Beginning ferry home.

002926 UTC (45.23274, -121.73640) 334.783°, 537.3 mb, 3658.0 m Switched to dual-PRF (3200/2133, Nyquist of +/- 48) for ferry. Setup file is MPRS1. Evidence of contaminated 1st trip echo (by 2nd trip) at 0034 etc etc.

004957 UTC (46.79881, -122.78369) 332.549°, 537.1 mb, 4679.0 m Radar system temporarily offline

010138 UTC (47.64162, -122.55238) 352.935°, 851.3 mb, 1146.0 m Back in echo, but no sign of 2nd trip, likely owing to low freezing level & absence of nearby terrain. Expecting 16R.

010848 UTC (48.11996, -122.34639) 67.652°, 884.8 mb, 779.0 m Secured radar system

011521 UTC (47.91954, -122.28584) 179.790°, 968.5 mb, 1.0 m Landed

S-Pol Radar Summary

The S-Pol radar was run continuously in the same mode of operation for the complete length of the field project.

Summary of Mobile Upstream Sonde Launches

Launch times at: Creswell, OR, Lat: 43.9200, Lon: -123.0250, Elev: 165 m

1726 UTC 28 Nov

1813 UTC 28 Nov

2051 UTC 28 Nov

Summary of Leeside Sonde Launches

Launch times at: Black Butte Ranch, OR (a.k.a. ISS-3), Lat: 44.379, Lon:-121.679, Elev: 1027 m

1530 UTC 28 Nov