Period Covered by this Report: 1 May 1998 to 30 April 1999

Date: 9 March 1999

1. This is collaborative research between groups at the Army Cold Regions Lab (CRREL), NOAA's Environmental Technology Lab (ETL), the Naval Postgraduate School (NPS), and the Cooperative Institute for Research in Environmental Sciences at the University of Colorado (CIRES) in what has come to be called the SHEBA Atmospheric Surface Flux Program.

We spent seven months of this budget year finishing the SHEBA field program. By the end of that field deployment, the four PI's in the Atmospheric Surface Flux Group, Ed Andreas (CRREL), Chris Fairall (ETL), Peter Guest (NPS), and Ola Persson (CIRES), had spent 10 man-months at the SHEBA ice station overseeing the day-to-day operations of the measurement program and assuring the quality of the data. Overall, personnel directly involved with our program spent over three man-years at the ice station during its year-long drift. The combined three-year NSF awards to our institutions for our SHEBA participation were not enough to cover personnel costs for the field program alone, so clearly our individual institutions have been cost-sharing with NSF and ONR to make SHEBA a success.

We had an extremely successful measurement program at SHEBA. The instruments on and around our main 20-meter tower collected 10 months (early November 1997 to late September 1998) of hourly averaged data with only a few interruptions when power went off during break-ups of the camp. Three of our four Portable Automated Mesonet Stations (PAM's), which were 1-5 km from the main camp, collected 10 1/2 months of hourly data. We estimate that, during the course of SHEBA, our program alone collected roughly 30 billion (i.e., 30,000,000,000) data points.

We are still processing data and applying quality controls. Several instruments underwent post-experiment calibrations that must be included yet in the final data files. We did place data from our tower for November and December 1997 in the SHEBA archive for preliminary analysis by the SHEBA community. The mean meteorological quantities measured by the four PAM stations for the entire year have also been deposited in the SHEBA archive. In addition, we have filled roughly a dozen personal requests from other SHEBA investigators for early access to our data. All of our data will be available from the SHEBA archive in October 1999.

A few observational highlights have come out of our preliminary screening of the data set. The ablation season essentially began in late May with a couple drizzle events. The drizzle wetted the previously white, bright snow surface and altered its albedo enough to produce a step increase in the absorbed shortwave radiation.

The near-surface relative humidity, when figured with respect to ice, was always virtually 100%. That is, contrary to being "dry", the lower Arctic atmosphere is in moisture equilibrium with the ice and snow surface. This finding may facilitate modeling; because now, rather than requiring humidity measurements, we can simply assume that the near-surface air always has 100% relative humidity with respect to ice.

Most of us have been taught for a long time that the net radiation budget is positive at lower latitudes but negative at high latitudes. Our year of net radiation measurements at SHEBA, however, suggests that the total net radiation during our SHEBA deployment was positive (i.e., surface gaining energy radiatively). It is not clear whether this positive budget is typical of SHEBA latitudes or whether the SHEBA year was anomalous. In comparing these SHEBA radiation data with a year of data from Russian drifting station North Pole 4 (NP-4), which was within 5° latitude of the North Pole in 1956 and 1957, we see similarities but also distinct difference. The two radiation series cross from negative to positive in spring and then back from positive to negative in fall on nearly the same dates. But the NP-4 series has a much lower summer maximum than our SHEBA series has and, thus, suggests a total yearly net radiation of roughly zero.

On our main 20-meter tower, we measured surface stress by eddy-correlation. The time series of these stress measurements show many "events" or storms during which the stress was about two orders of magnitude above the general background. In fact, this stress series shows precursors to the break-ups at the ice station in late January 1998 and in late March 1998. Just before these two break-ups, the daily averaged wind stress exceeded 0.3 N/m².

2. Our scope of work for year three is the same as in our revised proposal. Mainly, we will be preparing data sets for the SHEBA archive and beginning analyses described in the proposal.

3. No funds will remain uncommitted at the end of the budget year.

4. The third-year budget is as specified on our revised budget sheets dated 27 March 1997.

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Last update: 5/5/99
Please send all comments and suggestions to the author, Peter Guest,