Fire/SHEBA Spring Field Campaign 1998 Aircraft Observer Notes
By: William R. Cotton

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In May of 1998 my wife Vollie and I drove to Fairbanks, Alaska where I participated in aircraft flights in the NCAR C-130 as part of the FIRE/SHEBA field program to study Arctic stratus clouds. The following is my aircraft observer notes. For those interested in only the travelogue, I have prepared a separate file entitled "Driving, Ferrying, Flying, Kayaking, Biking, and Hiking Alaska 1998". For those of you interested in the whole story click here

The notes are all taken in Alaska daylight saving time and I indicate times of takeoff so that one can link the notes to the timing on all the aircraft files--just look at the aircraft takeoff time and adjust accordingly.

I bicycled over to Fort Wainright in about 30 minutes along a back road.

0745ADT Weather briefing for today's flight. Some cirrus patches along the way. Winds SE over the ship area, low-level fog, and stratus. Some leads but no major open water regions. Cloud bases at 1.75 km 300m thick, mixed phase. Our ETA 12:30, will do 20 km boxes, then long track through cloud when ER-2 is flying. Then a 50 km rastergrid (saw tooth). SW of ship sky is darker suggests an open lead. The ER-2, scratched because of too strong a cross wind today.

Sitting next to Jim Hudson and his CCN counter. This ship is very noisy already and the engines haven't started! I have earplugs on, compliments of NCAR.

0902 taking off from the Fort Wainright to Fairbanks Intl for fueling.

1024 Finally taking off from Fairbanks after being refueled. Jim Hudson is pounding on his instrument with a hammer! Interesting. 1048 Took picture of stratus with wave structure on top. Also took pictures on Yukon River. Then of Brooks Range. 1057 Took picture of lenticular from 22k ft over the Brooks Range. North of the Brooks Range it looks snowy, with a lot more cloud cover. Goodbye trees!

The view from the flight deck is great. Back in the cabin, I get a small view of the world through a porthole. It is pretty much cloud covered anyway. My GPS locked in fine from the flight deck but couldn't get a lock-on through the porthole.

1207 We've made it to 72 degrees latitude and 146 degrees 52 longitude. Still can see land--sort of. Now we are over the ice.

1229--Took photo of an open lead. Some of the leads are as wide as the Yukon; others appear as narrow cracks. no major open water areas.

12?2 We're now flying over what appears to be stratocumulus. 1245 We've made it to75 latitude; 162 degrees 31' long. A large number of leads are evident.

1302--We're over solid stratus and near the Sheba base. 76.01 lat;164-05lon.

1319 We're flying a boring radiometer sawtooth pattern at 15K. I gather the radiometer suggests that most of the leads are frozen over.

1344--Over some large open leads. You can see the low-level clouds over the open leads. Optically very thin.

1352 Descending through 3000 ft to do some low-level video mapping and then ascend to make cloud measurements. Tops at 1300 ft, We're at 300 ft over the ice. Cloud base was about 500 ft. Pretty darn thin cloud. Could barely feel turbulence in this massive beast! The cloud is multiple layered. Very thin layer at the top, then tenuous stuff down to 500 ft or so. No winds to speak of. Tops almost looked like K-H waves. Not likely. 1407 At 2000 ft into cloud. Sometimes beneath this first deck at 2100 ft. It is so thin I can see blue sky most of the time.

1414-Took photo looking up through upper level cloud.

1415-In and out of cloud at 1100 ft.

1421 Picking up some icing at 900 ft. Temp is 266. 1430 Passed over SHEBA ship at 300 ft got some photos. Great fun flying over the ice at 300 ft.

1437 At 700 ft in and out of cloud.

1441 150 ft right over the ship! Took lots of photos--What fun! In the clouds near the ship, the peak LWC was 0.2g/m**3 and peak LWC +IWC was 0.5. Tara didn't see anything bigger than 20 microns. Dave counted only 0.5/liter of IFN at -20C. Hudson saw CCN at 0.75 percent of 50/cc near the surface. Even the CN was only about that much. At 850mb he is seeing over 400/cc.

The ice surface appears to be generally smooth except near fresh or old leads where it is pretty jumbled up. Most of the leads are frozen over.

1522 Making several low passes over open leads. Low cu over the leads.

1540-47 Made 150 ft low passes over a large lead pond. No enhancement of CCN with very low counts but Dave observed his highest IFN counts so far of 30/liter at -20C. Winds over the lead were producing nice waves so they were probably 8-10kts. I saw the open lead pond on the way north and marked it on my GPS and directed the plane to it with my GPS.

1616, We did a last low pass over the ship and are now heading back.

0730 briefing. lots of cirrus and mid-level clouds. Then low-level stratus. Hobbs will fly this afternoon if a part for his plane arrives. The clouds suggest the presence of a weak shortwave but the models aren't picking it up. Planned flight pattern includes 5 km raster pattern, descend to 2.5 km and run east--west mapping patterns below the cloud. Then descend to 30m with low-level runs over open leads. Sample the leads. I suggested a run downwind side of lead about 30 km away but it looks like they will sample 1 km away, followed by a raster type pattern and a run right down the lead. Then ascend to the base of the altostratus about 50 km long at 1500 to, coordinate with the ER-2.

0852 Taking off from Fort Wainright and on to Fairbanks Intl for fueling. 1030 After a long refueling stop, and an almost scrubbed mission because of an ER-2 problem, we are finally on our way north.

1124 Just passed a small town on the northern fringe of the Brooks called something like Anatubik Pass. now that is one isolated place. Just an airstrip for access.

1157 Took a photo of the solid stratus covering the North Slope as far as the eye can see.

1207 Took photo showing lower albedo of cloud layer over open water along the coast.

1301 Still flying over solid stratus.

1308 there are patches of altostratus above the low-level stratus.

1310 The altostratus is now almost solid coverage.

1312 Beginning descent into the boundary layer.

1315 The altostratus layer ends abruptly to the north.

1317 There are a few cirrus patches overhead. Tara is seeing rosettas and other crystal clusters from the cirrus patches. 1320 The CPI was showing some riming on the rosettas and other crystal clusters.

1330 We've entered the alto stratus layer.

At 3300-4500m the layer was composed entirely of ice crystals of a few/ per liter. The low-level stratus was from 180m to 450m. We're now doing a low-level run.

1339 The CFD is measuring very low IFN conc's of 5/liter near the surface. Jim is seeing 50/cc CCN at 1 percent SS. 1343 outside temp near the ground is -5C and Tara is seeing occasional snow showers.

1350 The leads here are small and only partly open.

1351 The IFN is seeing about 9/liter at -21C which is a lot less than aloft where he was seeing 60/liter.

1400 The CCN conc's remain pretty uniform at 48-50/cc. IFN are a slightly higher at 12-15/liter at -21C.

1410 Cloud base about 200m, Drop conc's of 100/cc but fairly wet. Top of layer about 500m. CCN conc's higher above the cloud ranging to 150-160/cc. Since cloud droplet conc's are higher than sub-cloud air, it appears primary source of CCN is the entrainment from air above the cloud or at least inversion level air.

1440 At 480-500m is a strong temperature inversion as well as dew point.

1445 We 're right at cloud top at 500m with some big drops 30 microns are so. Possible evidence for radiation broadening of drop spectra.

1456 IFN conc's of 12-15/liter and CCN of 200/cc at 523m.

1459 at 300m, no big drops, temp, -5C. LWC of 0.1g/m**3 with 100/cc conc's. No realtime w measurements. Turbulence is light probably w-rms of 0.25-0.5m/s.

1511 Downwind of the ship you can see enhanced N conc's and depressed LWC??

1513 We're at 243m and in and out of cloud.

1517 CCN conc at cloud base is 60-80/cc. IFN still 10-15/L. Tara is seeing some 50 micron size drops. It feels like w is approaching 1m/s. The low cloud top temperatures were -10C.

1543 Surface temps are about -7C and open leads about -3C*.

1549 The vertical structure of the clouds have been consistent for the three or more soundings we have taken. Aloft, there is only patchy cirrus so the low level cloud is radiating to space for the most part.

1607 The altostratus layer has disappeared and it appears it has left behind enhanced CN concentrations. Possible evidence of cloud processing of aerosol?

1626 This is the boring part of the flight in which we fly above the clouds making radiation measurements for comparison with the ER-2.

1727 Took photo illustrating regularity of role structure of tops of stratus layer on our return ferry flight.

Dave said that in the layer 3.6-3.8 km there were higher concentrations of aerosol and IFN conc's jumped by a factor of 5 to about 30/L. This is probably the same layer that the NCAR CN counter showed a peak in CN of almost 400/cc in the layer 2.75- 2.9 km. Concentrations of CN above and below the layer were below 250/cc. I suspect Dave's altitude recollection was off.

It appears that I got here too late to see the mixed phase low-level stratus. The earlier flights exhibited mixed-phase structure, but now they are too warm. I gather the clouds are warming up faster than anyone expected. I may have to check with George Isaac of AES who has flown earlier flights in which the clouds were mixed phase.

1801 On our ferry back flying at 20,000 ft, Tara was seeing ice crystals in low concentrations in a sky that appeared cloud free at a temperature of -25 to -26C.

1914 Hudson is seeing widely fluctuating values of CCN at ferry level south of the Brooks Range. Sometimes as high as several hundred per cc and just a minute ago as low as5-6/cc. Cloud scavenging? I don't see any clouds here now.

Briefing. If it looks like it will be clear at the ship, then the C130

will fly tomorrow. I will not since I am interested in cloud flights, not boring radiation flights. If they don't fly tomorrow then they will definitely fly the C-130.

Overview--They have had five cases with leads. It is now too warm to get cloudy convective plumes. 1 liquid cloudy BL, 5 mixed phase cloudy BL, 2 cases of cirrus and altostratus; 1 storm; 2 multilevel clouds; 5 cloud physics and radiation.

Tara CPI summary--the 4 May case appears to be the best mixed phase case. Yesterdays case had only a few patches if ice crystals.

Hudson--vertical gradient of CN and CCN show factors of 4 to 10 lower conc's near the surface. Conc`s are generally uniform except for a few spikes.

Most CCN are sulfates based on volatility measurements. The CN are non volatile, possibly anthropogenic. he sees some evidence of lead sources of CCN.

Dave Rogers CFD measurements. Near leads IFN conc's jumped from near zero to 10 to even 100/L. On another day this did not happen possibly because the leads were frozen??

Afternoon briefing.

Dave Rogers said that the conc's of IFN were not enhanced over the open water along the coast near Barrow--interesting! The IFN conc's were a bit higher over the ship at low-levels, about 5-8/cc.

Hudson found the CCN conc's to be more uniform with height above the ship, consistent with the absence of cloud scavenging. There was also not substantial enhancement of CCN over the open water along the Barrow coast. As expected it was clear at the ship today.

The satellite shows it severe-clear over the ship today. I've decided to go along even though it won't be very exciting. I hope we find some low clouds near the coast on our return.

0854 Taking off for our refueling stopover at Fairbanks Int.

1008 Takeoff Fairbanks Int.

1055 Photo of the Brooks Range covered with lenticular patches. There are patches of cirrus precipitating crystals from above. We're flying at 18.9k. Dave is seeing IFN conc's less than 5/L--pretty low. CCN conc's are about 300/cc.

1111 Took pictures of images on Tara's CPI and one of the display console and of the radiometer mapper.

1113 As usual the North Slope is covered with low-level stratus.

1115 Photo of the North Slope stratus.

1133 Photo showing low albedo of clouds over the open water along the coast.

1200 the low-level stratus is starting to breakup, but patches of middle-level stratus remain. The ice looks much more broken up than it did a week ago. 1207 We're about 200 miles from the ship. There is a lot more open water than a week ago. There is one large river-like lead to our northeast about 70 miles.

1238 Photo showing broken nature of the ice about 20 miles from the ship.

1244 Marked the position of several open leads on our raster scale flight pattern.

1252 Photo of ship from 13.5k.

1304 There is still a discernable haze in the BL or at least the air immediately above the BL. No clouds are present anywhere near the ship.

1336 We're at 1.5 km in the stable inversion and seeing large fluctuations in CN. We're probably going in and out of the BL top.

1404 Passed over the ship at 600 ft.

1410 Seeing CCN conc's of 220/L and IFN at -17 and 7, percent SS with respect to water of 5/L.

1412 @ 300 ft. CCN conc has been pretty uniform with height at a couple hundred per cc at 1 per cent SS.

1421 Took some pictures of the ship in the sunshine at a balmy -5C.

1431 Took photo of ice from 50 ft, we're climbing to 700m.

1509 Beginning the next leg of the boring radiation raster grids.

1626 Took photos of the northern edge of a broken stratocumulus layer north of the Barrow coast.

1631 Took photo of cirrus ucinus fall streaks. There was a clear boundary north of Barrow in which the stratocumulus layer began. This is probably associated with the distinctly different low-level flow that Don Wyley showed with the model trajectories. Worth investigating the synoptic/mesoscale dynamics that drives this change in clouds/circulation. We're now descending but I'm not sure what the flight plan is.

1443 Close up view of tops of cloud layer near Barrow.

1446 The layer is quite broken and occasionally I can see the ground through the cloud layer.

1649 Tara said the cloud is mixed phase. We descended through cloud and we are still over the ice. We are going to stay at 1500m which is below cloud base. Hudson said CCN conc's are about 300/cc both below and above cloud top, a little higher than over the ship. Cloud top T is about -8C and IN conc's are about 10/L at -19C. The LWC plot looks like we descended through 5 or more layers, with the most distinct three layers exhibiting peak values of about 0.15g/m""3.

1704 Photo of northern edge of stratocumulus layer taken from 4800 ft. This is pretty close to cloud base. One can see the distinct altocumulus layer above this flight level.

1709 Photo looking north showing the distinct layering of the clouds.

1712 11.5K to 12K ft is the altocumulus layer with cirrus above. Heading 140 degrees.

1716 pos:73deg 06.99min4 159 deg 36.04 in cloud at 10.4K ft. Droplet conc is 250/cc. The LWC peaked between 0.15 and 0.2g/m**3. Tara showed me this odd-shaped ice particle that must have been some kind of sublimated ice crystal.

1902 It appears that in all these clouds, the primary source of CCN and IFN is the air in the inversion via cloud top entrainment. This is because the clouds have scavenged out the ABL and they are for the most part decoupled from the surface, which has only weak sources of CCN and IFN at best.

This makes me think of the Hobbs-Rangno experiments where they measure the rapid formation of ice crystals in cumuli at the time the clouds begin to dissipate. Perhaps these cumuli are dissipating because they are entraining inversion air where there are enhanced concentrations of aerosol including IFN. Thus as the clouds entrain dry, stable inversion air, they also entrain High IFN conc's which lead to vigorous activation of ice crystals by deposition/ condensation-freezing and/or contact nucleation. Dave Rogers and I should design a field experiment to test this hypothesis.

0800 Weather briefing for the last flight of the spring phase.

There is a short wave moving through the ship region. Right now there are multilevel clouds, some of which appear to be deep convective cells. In addition, there is freezing rain at the surface. Winds at the surface are SE at 18knots, very different than my earlier flights. One consequence of the freezing rain is that the surface albedo is expected to decrease from its current values of 0.82.

Proposed patterns:

50 km raster grid at 6 km descend to 4 km; below base of upper cloud top. Another raster type grid at lower levels, cloud penetrations, and low-level runs.

0852 Takeoff from Fort Wainright.

1020 Takeoff Fairbanks Int.

1051 Tara is displaying all sorts of complicated shaped ice crystals as we passes through altostratus on our ferry north. I'm getting to be able to tell when we are in subsaturated regions just by looking at the CPI images. As the crystals sublime they lose their sharp-edged structure and metamorpholize into rounded rather strange looking crystals. We've been flying at 20K ft over the Brooks Range.

1150 Took photos of open water and ice flows north and west of barrow.

1210 We're now flying over what appears to be solid boundary layer stratus.

1213 Took photo of the stratus deck. But, I doubt it came out well because there is a deep haze layer that extends up to our flight level of 20K ft.

1217 Took photo showing holes in the cloud deck that allows seeing the ice below.

1241 Current location of the ship is 76deg 32.55min N; 168deg 0.08 min W

1245 We're about 15 min from Sheba and still over solid stratus. There is an elevated haze layer what appears to be close to our altitude. Below that I can see clear sky except for the BL stratocumulus.

1250 There are some patches of altostratus (5-10K ft??) above the BL stratus.

1252 We're beginning the raster pattern.

1257 At flight level 20Kf ft we're seeing IFN conc's of 40/L at -16C which is pretty high. Hudson's CCN counter is showing conc's of 775/cc which are also high. This is probably related to the haze layer I mentioned earlier. CN conc is almost 10,000/cc.

1307.winds at flight level 103@28kts. Are there forest fires SE of us??

1313 Photo showing haze layer we are flying in and BL stratocumulus below.

1319 Photo showing pop can as a "high-tech" component of Jim's CCN counter.

1323 Photo showing edge of slightly higher cloud extending in a roughly 210 to 030 direction. This band of deeper cloud extends north for 50 or 60 km where it appears to open up to the low-level cloud again.

Some places where the higher level cloud opens up it looks like a cloud "canyon". I wonder if the canyons are locations where the cloud has glaciated? Nope, as seen below temp's are warm.

1337 Took photo of narrow opening in cloud that looks like a ship track but it doesn't seem to be tied to the ship at all.

1339 photo showing mesoscale structure to the cloud organization.

1341 We're heading right towards the edge of the higher cloud structure. We're at 7000 ft, a 1000 ft or so above the deeper cloud layer. Cn conc 7982, CCN 470, ?? Temp is a balmy -1.7C!

1653 Photo showing multi-layered structure of cloud to our SE.

1700 descending through the cloud. Tara is seeing 100 micron drizzle drops so what I inferred as "glaciation" is actually "drizzlization". We've gone through 3 layers of cloud so far. It is very clean CCN conc has dropped to less than 50/cc.

1406 There are 2 major peaks in LWC one at 1500m and another at 200m with peaks of 0.2g/m**3. We descended to 300m.

1415 at 5700 ft and right at cloud top and the entrainment interface zone.

1427 We climbed to 5700 ft and are now descending.

1434 We're at 3000 ft and flying beneath an altocumulus layer and above the stratus layer.

1436 Photo shows us in the cloud sandwich!

1449 Flying just above cloud top--CCN conc over 400/cc; CN conc over 10,000/cc and 'not much IFN'.

1458 We're now at 2500 ft and can occasionally see the ice surface. It is very broken up compared to the last flight. Turbulence is very weak here compared to near cloud top.

1513 At 1800 ft and in and out of cloud.

1517 Photo from 1800 ft shows the partly cloudy BL.

1519 We've descended to 1400 ft and in and out of cloud.

The CCN conc is down to 25-35/cc and CN of less than 300/cc. Droplet conc's are about 120/cc.

1529 We're now at 1100 ft and still in and out of cloud wisps.

1532 Photo showing the stratus deck above, and the broken cloud that we are in plus the ice surface.

1536 at 700 ft and still in and out of cloud wisps; a bit like driving in fog.

1543 The larger leads are frozen over, only the small ones are partly open.

1544 at 400 ft approaching ship.

1556 at 250 ft .

1558 photo of open lead from 200 ft.

1615 Been making 100 ft passes over leads which are hardly open at all. CN count is less than 1000/cc and CCN is less than 50/cc. IFN conc's are running about 8/L.

As I recall(I'm adding this later) on the ferry back to Fairbanks at 18Kft, Hudson was seeing wide variations of CN and CCN ranging for CN from something like less than 50/cc to values over 700/cc. I suspect that we were flying across mountain patterns as there was considerable lenticulars beneath us. What I think was happening is that we were flying close to the tropopause and the wave was at time made up of stratospheric aerosol and at times made up of tropospheric aerosol.

1644 We're on the way back. This completes our flights for the spring season. I suspect the summer won't be too different because it was anonymously warm this spring. The leads should be more open in the summer, though.

I didn't get the impression that the leads were all that important as the coverage of truly open leads is very low. Moisture is probably supplied by horizontal advection more than lead fluxes. And CCN and IFN are probably supplied by entrainment from the dirtier air above the inversion. Likewise for the period I was here, the ice phase was only of consequence in the higher level clouds and not boundary layer clouds unless it was through a seeder-feeder mechanism. We shall see when we go through the numbers.

1756 To my surprise we're cruising at 35m above the ice just to the NW of Barrow. We are now going over large open water patches. 1751 Took photo of the beach near Barrow--anyone for sunbathing?

That ends the Spring 1998 FIRE/SHEBA field campaign.