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NASA - AMISA Science Report #5, (Flight #6), Aug. 25, 2008
September 11, 2008
 

NASA's DC-8 airborne laboratory completed the fifth and final dedicated data flight of the Arctic Mechanisms of Interaction between the Surface and Atmosphere (AMISA 2008) project on Aug. 25, 2008. The DC-8 was in the vicinity of the Swedish research vessel Oden for almost five hours. The 10.6-hour flight out of Kiruna, Sweden was timed to sample low level Arctic stratus under non-frontal conditions and to map the surface sea ice state under post-freezeup conditions.

The synoptic state was characterized by dry air advecting from the west-southwest over the Oden, over which a pressure ridge was beginning to form. An unexpected jet streak and an attendant frontal wave produced some high clouds and low-level frontal-like structures for the first two hours the DC-8 was in the vicinity of the Oden. A high-altitude mapping grid and racetrack patterns at several fixed and varying altitudes were flown in the vicinity of the Oden.

In planning for this flight, forecast moisture and flow conditions were deemed optimal for low-level Arctic stratus formation, although in general it is exceedingly difficult to forecast this type of cover. Accordingly, the cloud conditions actually encountered were that of inhomogeneous low-level stratus modified by the influence of at least two air masses advecting from slightly differing directions. The inhomogeneous conditions were noted north of Svalbard, where long waves of stratus punctuated by clear air were observed. Inhomogeneities were further observed within the racetrack sampling patterns around the Oden where higher clouds and moisture were noted to the north and northeast of the ship. Upon descent the stratus deck top at about 1.9 km (6,200') was clear above, and thus dominated by cloud-top radiative cooling.

The high-altitude mapping grid consisted of three flight lines and covered an area of 250 x75 km. The grid was aligned with the Advanced Microwave Scanning Radiometer – EOS, or AMSR-E, product grid for use in satellite algorithm validation studies, and covered 20 x 6 =120 pixels. While executing this pattern, five sondes were dropped over the Oden, one at each corner and one in the center, to characterize the synoptic flow and inversion height field around the Oden.

In addition, two each sondes were dropped enroute inbound toward and outbound from the Oden area. The sonde dropped at the southeastern corner of the high altitude grid showed an inversion top of 1.0 km and a cloud top of only 0.5 km, with a dry layer between 500 m and 2,200 m. The western and northern area of the flight pattern were not covered by upper-level clouds and showed low-level stratus clouds with tops near 1,200-1,500 m and a sharp but shallow cloud-top inversion near 1,500 m. This latter cloud structure was the one primarily sampled by the later racetracks.

The first low-altitude racetrack was flown using a sawtooth pattern to provide maximum information on the vertical distribution of cloud and condensation nuclei, or CN. During these sawtooths, a strong correlation was noted between the occurrence or absence of large CN concentration and the presence or absence, respectively, of clouds and moderate amounts of cloud liquid water. These correlations were observed on sawtooth lines between ~600-900 m (~2,000'-3,000') altitude and for cloud liquid amounts of ~0.1-0.15 g/m^3 . Larger cloud liquid amounts (up to ~0.35 g/m^3 ) were observed near the cloud tops. The measurements were mostly of volatile CN, and provided the strongest evidence to date of the importance played by CN in Arctic cloud development. An abundance of CN were observed at transit altitude of about 9.7 km, or 32,000' en route to the Oden over Svalbard, although this upper tropospheric CN did not play a role in the inversion layer cloud dynamics.

Upon completion of the sawtooth pattern, the altitudes of the two mid-cloud racetrack patterns were selected to be ~600 m (~2,000', or within the cloud at the top of the mixed layer), and ~1,000 m (3,300', or just above the cloud layer). First, a ~100 m (350') altitude racetrack pattern was flown during which significant volatile CN concentration and sea ice state was observed. The two successive racetracks at higher altitude produced Clarke probe icing that compromised the LARGE and VACC data, but not before registering significant CN concentrations at the top of the mixed layer at about 600 m altitude. Attempts to take data at 1,000 m altitude led to strong probe icing, which was unable to be shed completely even upon ascent to above the clouds at 1,200 m. Accordingly, the 1,000 m altitude racetrack was called off.

A final 1.7 km (5,500') altitude racetrack was flown to complete AMISA mapping requirements, followed by a 1.3 km (4,000') leg where good VACC and LARGE data were acquired, and a final short sawtooth line oriented orthogonal to the previous lines so as to measure CN concentrations along the flow over the Oden. Again, CN spikes were observed at ~730 m (~2,400') altitude within clouds with liquid amounts of ~0.15 g/m^3 .

During the flight, post-freezeup conditions were predominant around the Oden. The surface was observed to be mostly frozen over by heavy grease ice on all but the largest leads. In some of these partly open cases, the grease ice protruded from the lead edges by tens of meters. Surface reports at the Oden suggested ~5 cm thick ice cover over leads that required the use of swimmers to break up for in situ sampling. All meltponds were frozen over and covered with snow. Accordingly, aerosol production and heat and moisture transfer from the surface was largely precluded. As in the previous Oden flight, the surface albedo was noticeably higher than during the two Oden flights at the start of AMISA.

Although icing on the Clarke probe inlet prevented complete aerosol characterization by VACC and LARGE on the mid-level racetracks, good data was observed by these instruments during all other racetrack and sawtooth lines. The ice buildup was well documented with photos and believed to be resolvable upon outfitting the probe inlet with appropriate heaters. Also, one dropsonde failed upon release, but was immediately re-launched. Otherwise, all instruments exhibited normal operation during the flight. Remnant data from the sonde dropped over the Oden was received upon closest approach about 1.5 hours after release.

The DC-8 AMISA campaign is part of a NASA-sponsored International Polar Year (IPY) project with the goal of understanding the surface and atmospheric radiation and dynamical processes leading to Arctic sea ice freezeup. Research activities on the Oden are sponsored by the Swedish Polar Secretariat, with support from European funding agencies and the U.S. National Science Foundation and the National Ocean and Atmospheric Administration. AMISA participants include personnel from the University of Colorado, the University of Leeds, the Georgia Institute of Technology, and NASA's Dryden Flight Research Center, Goddard Space Flight Center and Langley Research Center.

The first of two AMISA transit flights back to the U.S. occurred on Thursday, Aug. 28, with customs entry in Bangor, Maine. Final reports on this flight and the final return flight to Palmdale on Friday, Aug. 29, are forthcoming. Also forthcoming is a post-mission synopsis covering the entire set of AMISA flights.

Al Gasiewski, Ola Persson
Principal Investigators, AMISA 2008

Professor Albin J. Gasiewski, Ph.D.
Director, NOAA-CU Center for Environmental Technology (CET)
University of Colorado at Boulder
al.gasiewski@colorado.edu
 


AMISA Mission Science Report #4, (Flight #5), Aug. 23, 2008

NASA's DC-8 flying science laboratory completed the fourth dedicated data flight of the Arctic Mechanisms of Interaction between the Surface and Atmosphere (AMISA 2008) project on Aug. 23, 2008. The DC-8 was in the vicinity of the Swedish research vessel Oden for almost 3.5 hours.

The 8.7-hour flight out of Kiruna, Sweden was timed to observe clouds over the Oden associated with the moist air mass observed in the Fram Strait on the previous day's flight during the ice edge mapping mission. This moist air mass had moved north to the Oden, which was located near the western boundary of the air mass.

The flight was designed to study Arctic air mass divergence profiles, Arctic cloud microphysical properties and radiation profiles within clouds, and aerosol transport trajectories and their impact on liquid water production in Arctic clouds. The surface around the Oden was experiencing freezeup, thus fulfilling an important AMISA observation condition. This was also the first AMISA overflight of the Oden during which all ship instruments were in operation.

The sampling domain around the Oden was located near a frontal boundary with a complex vertical structure that varied from west to east across the sampling area. In the eastern portion of the flight pattern near the Oden, the cloud tops extended to nearly 4000m with uniform south-southwest flow throughout and near moist neutral static stability. The air mass on the western side of the flight pattern had slightly colder near-surface temperatures, and had a shallow moist layer near the surface and only one cloud layer near 3500-4000m above. The air mass on the western side also had winds from the southeast and greater static stability.

Over the Oden, a cloud layer near 1500m was present. Moist static neutrality was present above this layer and moist static stability existed below. The inversion layer altitude as measured at the Oden was at ~250-300m. The eastern side and levels from 1500m and above over the Oden had characteristics of the moist air mass sampled the day before while the western side was different. Oddly enough, the winds obtained from the dropsondes suggested diffluence – or spreading of the wind vectors – near this front throughout the 4km depth of the clouds.

Surface observations showed virtually all meltponds completely frozen over, with leads showing significant coverage by grease ice. Lead surface conditions indicated freezeup in progress, with limited moisture, heat, and aerosol transfer taking place. To the northwest of the Oden, the grease ice coverage was ~80-100%. Ice floes were covered with fresh snow, and exhibited a noticeably higher albedo than during Oden overflights more than a week earlier.

Three patterns were flown over the Oden: A high-altitude Z-box survey pattern, and low-altitude sawtooth box centered around the Oden for cloud microphysical, low-level divergence, and aerosol condensation nuclei (CN) sampling, and a stacked set of straight and level and sawtooth lines over the Oden for cloud radar validation purposes. A total of 11 sondes were released during the flight, including five during the Z-box survey pattern used for synoptic assessment. During the Z-box, the PSR instrument was performing wide area mapping using the Advanced Microwave Scanning Radiometer - EOS (AMSR-E) passive microwave radiometer imaging channels. Observations during this pattern showed enhanced cloud water and likely precipitation southwest of the Oden.

During the sawtooth box pattern, distinct repetitive layers of CN at 1300-2000m altitude were observed, but only on the two southeastern sides of the box. The advection and falloff of CN is hypothesized to have been a cause of significant liquid water over the box, observed to be as high as 0.1 to 0.2 g/m^3 on the east end. Upon ascent, the cloud liquid water was noted to increase from 0 to ~0.2 g/m^3 , consistent with Arctic cloud models that place the liquid thermodynamic engine of the inversion layer at the cloud top.

During low altitude (110 m) lines, large CN concentrations were also observed, and determined to be mostly volatile in composition. Interesting dropouts in CN concentration were also noted in this line. These dropouts are conjectured to be caused by subsidence that would suppress aerosol production from any open leads. Careful analysis of the meteorological structure will be required to understand the observed aerosol variability in the vicinity of this layered interface between two air masses.

All instruments exhibited normal operation during the flight, with the exception of one failed dropsonde that needed to be repeated. The failure was traced to an antenna connection problem known to be present on a few sondes. Pre-flight repairs of the CAPS particle size imager were successful, resulting in good cloud size spectra measurements.

The DC-8 AMISA campaign is part of a NASA-sponsored International Polar Year (IPY) project with the goal of understanding the surface and atmospheric radiation and dynamical processes leading to Arctic sea ice freezeup. Research activities on the Oden are sponsored by the Swedish Polar Secretariat, with support from European funding agencies and the U.S. National Science Foundation and the National Ocean and Atmospheric Administration. AMISA participants include personnel from the University of Colorado, the University of Leeds, the Georgia Institute of Technology, and NASA's Dryden Flight Research Center, Goddard Space Flight Center and Langley Research Center.

The last AMISA science flight occurred on Monday, August 25, over the Oden. The report on this flight is forthcoming.

Al Gasiewski, Ola Persson
Principal Investigators
AMISA 2008

Professor Albin J. Gasiewski, Ph.D.
Director, NOAA-CU Center for Environmental Technology (CET)
Department of Electrical and Computer Engineering
University of Colorado at Boulder
Boulder, CO 80309-0425 USA
al.gasiewski@colorado.edu




AMISA Mission Science Report #3, (Flight #4), Aug. 22, 2008

NASA's DC-8 airborne science laboratory aircraft completed the third dedicated data flight of the Arctic Mechanisms of Interaction between the Surface and Atmosphere (AMISA 2008) project on Aug. 22, 2008, after being postponed on Aug. 19 due to weather conditions. The 8.7-hour flight out of Kiruna, Sweden provided radiometric mapping of an area of strong sea ice concentration gradient under conditions of heavy and homogeneous cloud cover.

The sea ice edge on the east side of the Fram Strait ice tongue was selected as the target area due to strongly varying ice concentration, open ocean location, and accessibility from Kiruna. The mapping grid extended from open water east of the ice tongue in the Fram Strait to concentrated sea ice within the ice pack. A heavy stratus cloud layer over the entire grid provided near-ideal conditions within which to study the impact of clouds on the NASA Advanced Microwave Scanning Radiometer - EOS (AMSR-E) passive microwave radiometer sea ice retrievals. The homogeneity of the southerly flow of moisture was important for providing uniform cloud conditions over both the open water on the southeast portion of the grid as well as the concentrated ice in the Fram Strait ice pack at the northwest end of the grid.

Two complete mapping grids were flown during the sortie: a 3-line grid at 8800 meters altitude covering 250 x 75 km and a nine-line grid at 1700 meters covering 125 x 40 km. These grids correspond to 20 x 6=120 and 10 x 3=30 AMSR-E pixels, respectively. In addition, three 125-km long sub-tracks of the high altitude grid lines were flown at 110 m altitude to measure the total cloud liquid and moisture burden from the surface upwards in the grids.

The total column cloud liquid water and moisture will provide validation data for the atmospheric correction portion of the AMSR-E sea ice concentration algorithm. The total burden is also important for radiative transfer calculations used in satellite inter-comparisons. The maximum sea ice fraction occurred on the west end of the high altitude grid, and was ~75-85 percent. Open water occurred on the east end. The meltpond coverage fraction relative to the lead area was visually estimated to be between ~5-25%, depending on location within the grid.

During the flight, cloud over the area was caused by southerly flow of moisture from a major low-pressure system located southeast of Svalbard. The flow produced stratus extending from ~1600 m up to ~3600 m altitude. Thin higher clouds existed above the eastern side of the stratus deck; slightly greater cloud top liquid and probably radiative cooling existed on west end. Cloud extended to the surface on the west end. The cloud liquid water distribution was noted to be increasing with altitude from near zero at 1300 m - 1600 m and peaking at ~0.3-0.5 g/m^3 at the cloud top (~ 3600 m). This structure is consistent with Arctic cloud profiles in which production of liquid water occurs at the cloud top. The cloud liquid water profiles obtained during the flight are expected to be particularly valuable for radiative transfer calculations and associated retrieval algorithm improvement.

All of the DC-8 instruments operated well throughout the flight with the exception of the particle imaging and large-particle size distribution instrument on the CAPS probe. The CAPS imager suffered an optical misalignment that was corrected after flight. However, it is expected that measured cloud size spectra were compromised during the flight. During the flight three dropsondes were released in order to assess cloud thermodynamic conditions and layering. Two of the three sondes apparently landed intact on the ice and transmitted remnant signals to the DC-8 for up to 4.5 hours after release.

As in previous AMISA flights, this flight was very well managed and accomplished both satellite algorithm validation objectives along with cloud microphysical observations useful for AMISA cloud radiation studies. The timing of the flight with respect to cloud evolution and grid coverage was excellent from the standpoint of mapping goals.

The mapping flight fulfilled a major goal of AMISA in providing data by which to improve AMSR-E sea ice retrieval algorithms by providing a better understanding of the effects of clouds and precipitation on the AMSR-E high frequency microwave channels. Although the best spatial resolution is available from the highest-frequency AMSR-E channels (37 and 89 GHz horizontal polarization), it is these same channels that are most affected by cloud cover. Development of improved means to compensate for cloud cover is expected to lead to more accurate retrievals in marginal zones and better spatial resolution for detecting leads over pack ice.

The DC-8 AMISA campaign is part of a NASA-sponsored International Polar Year (IPY) project with the goal of understanding the surface and atmospheric radiation and dynamical processes leading to Arctic sea ice freezeup. AMISA participants include personnel from the University of Colorado, University of Leeds (UK), Georgia Institute of Technology, and NASA's Dryden Flight Research Center, Goddard Space Flight Center and Langley Research Center.

The next AMISA science flight occurred on Saturday, August 23, over the icebreaker R/V Oden. A report on that mission will be posted shortly.

Al Gasiewski, Don Cavalieri, Ola Persson
Principal Investigators, AMISA 2008
al.gasiewski@colorado.edu
NOAA-CU Center for Environmental Technology
University of Colorado at Boulder






AMISA Mission Science Report – Flight #3

NASA's DC-8 airborne laboratory completed the second dedicated data flight of the Arctic Mechanisms of Interaction between the Sea and Atmosphere (AMISA 2008) project on August 15, 2008. The 11.2-hour flight out of Kiruna, Sweden was designed to provide synoptic-scale post-frontal observations of a plume of cold, dry air that originated from Greenland and flowed northward along the Fram Strait towards the Swedish research vessel Oden.

The edge of the Arctic ice tongue in the Fram Strait is seen in this photo from NASA's DC-8 flying laboratory.The edge of the Arctic ice tongue in the Fram Strait is seen in this photo from NASA's DC-8 flying laboratory. (NASA photo) Aerosol sampling was performed during three sets of stacked flight lines enroute to and over the Oden to determine the density and composition of biogenic and maritime aerosol flow into the near-polar Arctic inversion layer from the free troposphere. This aerosol is hypothesized to feed the development of Arctic clouds by providing condensation nuclei to seed the growth of liquid water droplets. The flight was performed during pre-freezeup conditions over most of the observed domain, as evidenced by the widespread presence of leads from the Fram Strait ice edge to the Oden. The presence of grease ice on most of the meltponds observed at low altitude at the Oden and the second stack suggested, however, that freezeup was incipient (see photo).

The aerosol sampling stacks were located at three points:


  1. over open water in the northern Fram Strait,
  2. over broken first-year pack ice midway from open water to the Oden
  3. directly over the Oden.

Bracketing each stack were dropsonde releases that were used along with aircraft meteorological data obtained during descent and ascent to estimate the height of the mixed layer and direction of flow. A total of four dropsondes were released. The flight lines within each of the stacks were aligned orthogonal to the prevailing flow to provide maximum averaging of cross-stream flow variations, and hence the best average representation of aerosol characteristics within the flow. Altitudes of the lines were determined to provide sampling of the boundary layer at abut 350' altitude, the mixed layer between 2,500' and 3,000' altitude and the air immediately above the low level clouds and inversion layer at about 5,500' altitude.

Evidence of maritime biogenic aerosols was observed within the boundary and mixed layers at each stack, with methylsulfonic acid (MSA) and possibly sulfuric acid (H_2 SO_4) and biogenic carbon being detected. Despite strong maritime flow, a decided lack of salt aerosols was observed. This observation was consistent with insufficient whitecapping in the Fram Strait. A complex aerosol composition was observed at 5,500' over the Oden, with a gradient increasing in concentration toward the western end of the line. Overall, the observations were suggestive of well-contained transport of maritime aerosols to the Oden by flow within the mixed layer. Although a change in cloud concentration confounded aerosol measurements during the lowest line over open water, good sampling was obtained by the VACC and LARGE instruments on all other lines.

Meltponds and leads in the Arctic ice cap show evidence of refreezing in this photo from NASA's DC-8 airborne laboratory.Meltponds and leads in the Arctic ice cap show evidence of refreezing in this photo from NASA's DC-8 airborne laboratory. (NASA photo) In addition to aerosol sampling, the DC-8 completed a seven-line sea ice imaging grid over the Oden at 5,500' altitude to map sea ice cover around the Oden during post-frontal conditions. The grid covered the same lines as flown during pre-frontal conditions on Aug. 12, thus providing data necessary for inter-comparing ice concentration before and after the frontal passage on the 12th . The clear and consistent nadir video imagery of leads and meltponds during low-altitude lines is expected to be valuable for determining lead and meltpond fraction for retrieval algorithm development. The low-altitude stack lines also facilitated observations of the structure of the Fram Strait ice tongue through which much Arctic ice ultimately flows as a result of transpolar drift (see photo).

During overflight, the Oden was moored to an ice floe at 87.40ºN latitude, 5.77ºW longitude. The Oden had a number of instruments operating, including the millimeter-wave cloud radar, 449 MHz wind profiling radar, S-band precipitation radar, sodar, and 60-GHz profiling radiometer. Setup of the remaining ASCOS instruments was proceeding but hampered by the presence of two polar bears.

As in the previous (pre-frontal) flight, this flight was very well managed and accomplished multiple science objectives over the Oden and within the stacks enroute. The timing of the flight was again excellent from the standpoint of AMISA science goals, with sampling of the mixed layer flow being performed along a long band of well-defined southerly flow.

Most of the DC-8 instruments operated well throughout the flight. During one Oden overpass at 2,800' the VACC and LARGE instruments were largely inoperative due to ~75% probe icing, but recovered upon ascent out above the low level cloud layer. At this level the cloud liquid was supercooled and the water content was noted to be ~ 0.05 g/m3 at the western end and 0.25 g/m^3 at the eastern end, as measured by the CAPS probe. This gradient appeared to be associated with longwave radiative effects from an upper-level cloud layer over the western half of the leg.

The DC-8 AMISA campaign is part of a NASA-sponsored International Polar Year (IPY) project with the goal of understanding the surface and atmospheric radiation and dynamic processes leading to Arctic sea ice freezeup. Research activities on the Oden are sponsored by the Swedish Polar Secretariat with support from European funding agencies, the U.S. National Science Foundation and the National Ocean and Atmospheric Administration (NOAA). AMISA participants include personnel from the University of Colorado, University of Leeds (UK), Georgia Institute of Technology, and NASA's Dryden Flight Research Center, Goddard Space Flight Center and Langley Research Center.

The AMISA science flight planned for Tuesday afternoon, August 19, was scheduled to map the sea ice edge in the northern Fram Strait under conditions of heavy clouds. The mapping activity will serve to improve NASA satellite imaging of sea ice concentration by providing a better understanding of the impact of clouds and precipitation on the AMSR-E high frequency microwave channels.

Al Gasiewski
Principal Investigator, AMISA mission
Director, NOAA-CU Center for Environmental Technology (CET)
University of Colorado at Boulder
al.gasiewski@colorado.edu
 




AMISA Mission Science Report – Flight #2

NASA's DC-8 airborne laboratory was photographed from the bridge of the Swedish research vessel Oden as it made a low pass adjacent to the ship, moored in the Arctic ice fields during the AMISA science mission.NASA's DC-8 airborne laboratory was photographed from the bridge of the Swedish research vessel Oden as it made a low pass adjacent to the ship, moored in the Arctic ice fields during the AMISA science mission. (NASA photo) The NASA DC-8 aircraft completed the first dedicated data flight of the Arctic Mechanisms of Interaction between the Sea and Atmosphere (AMISA 2008) project on August 13, 2008. The 9.8 hour flight out of Kiruna, Sweden, was timed to coincide with passage of a major warm moist air plume originating from Siberia over the Swedish research vessel Oden. The midtropospheric plume produced significant clouds and precipitation over the DC-8's observation grid, centered over the Oden.

The flight served a number of science objectives, including observations of prefrontal and frontal conditions, air sampling in and above the Arctic inversion layer at several altitudes, wide-area mapping of sea ice cover, clouds, and moisture, and profiling of the Arctic inversion layer across a strong frontal gradient. Sampling of the atmosphere and surface imaging across the area of frontal flow enroute to the Oden was also performed. The area enroute was characterized by significant sea ice divergence and associated developing lead structure. The flight was exceptionally well managed, especially given the complexity of the sampling plan, multiple science objectives, and timing of the flight with regard to the evolving weather. A total on-station time of ~3.5 hours around the Oden was achieved.

The frontal band around which the flight was planned was typical of major polar storm activity known to disrupt the radiation balance within the inversion layer and lead to freeze-up. The flight occurred during pre-freeze, as was evidenced by a preponderance of leads and meltponds in the vicinity around the Oden. However, evidence of incipient freeze-up was observed as a ubiquitous presence of grease ice on meltponds and leads. Accordingly, the timing of this flight was excellent from the standpoint of AMISA science goals being that observations were carried out during critical sea ice and inversion layer transition conditions.

A total of seven dropsondes were released during the flight: three enroute to the grid within the frontal band, two over the Oden as the front passed the sampling grid, and two enroute to back to Kiruna within the pre-frontal wrap-around flow. Two well-defined inversion layers within the front over the Oden were clearly seen in the soundings. Within the inversion layer, icing conditions were present, but mostly on west (prefrontal) end of grid, whereas warmer air was observed on the east (frontal) end. Moderate amounts of total cloud liquid water (up to ~0.5 g/m3) were observed at 5,500'.

Alignment of the DC-8 sampling grid was chosen to provide atmospheric cloud and aerosol sampling along tracks orthogonal to the low-level flow around the Oden. As such, the sampling strategy provided good signal-to-noise conditions along tracks for aerosol measurement (i.e., long sampling time along an aerosol contour) and precluded contamination of atmospheric chemistry sensors operating on the Oden. Both sea salt and biogenic sulfate aerosols were observed within the upper part of the inversion layer, providing evidence of trapped long-range transport of natural cloud-producing aerosols. The source may have been the Kara and Laptev Seas, which are ice-free along the Siberian coastline, as the high wind-speed low-level prefrontal flow traversed it along its trajectory to the Oden site. This low-level prefrontal flow ended up in the warm layer at the top of the inversion over the Oden.

The Oden overpass occurred at 2100Z, and was coordinated using both aircraft-to-ship Iridium and VHF radio communications. In-flight updates on the ship's position and operations were essential to achieve an overflight that passed within ~5 nmi of the ship and a coordinated release of a rawinsonde from the Oden.

From the time the Oden had moored to an ice floe (~12Z) until the DC-8 overpass time (~00Z) the ship drifted southeast with the ice pack a distance of ~5 nmi. The low altitude (400') line was accordingly shifted south during flight to accommodate this drift, resulting in a closest overpass occurring ~200 m downwind of the Oden and at ~350' altitude (see photo). Most DC-8 instruments operated exceptionally well throughout the flight.

Among problems being diagnosed are data acquisition failures on the C-band radiometer. The LARGE and VACC sensors were unable to operate at 2,500 feet altitude due to icing of the Clarke inlet probe, although this problem was resolved upon ascent to warmer air above the inversion layer. The utility of in-flight data network in downloading updated MODIS satellite maps was again clearly demonstrated. Also useful was an in-flight spreadsheet program to lay out and overlay the evolving Oden grid pattern on the Google Earth in-flight position display.

The DC-8 AMISA campaign is part of a NASA-sponsored International Polar Year (IPY) project with the goal of understanding the surface and atmospheric radiation and dynamical processes leading to Arctic sea ice freezeup. Research activities on the Oden are sponsored by the Swedish Polar Secretariat, with support from European funding agencies, the U.S. National Science Foundation and the National Oceanic and Atmospheric Administration (NOAA). AMISA participants include personnel from the University of Colorado, University of Leeds (UK), Georgia Institute of Technology, and NASA's Dryden Flight Research Center, Langley Research Center, Ames Research Center and Goddard Space Flight Center.

The next AMISA science flown on Friday morning, August 15, observed what was forecast to be drier and colder air flowing from the Fram Strait to over the Oden.

Al Gasiewski
Principal Investigator, AMISA mission
Director, NOAA-CU Center for Environmental Technology (CET)
University of Colorado at Boulder
al.gasiewski@colorado.edu



 
 
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