Guðrún Nína Petersen

Ash generation and distribution from the April-May 2010 eruption of Eyjafjallajökull, Iceland

The 39-day long eruption at the summit of Eyjafjallajökull volcano in April–May 2010 was of modest size but ash was widely dispersed. By combining data from ground surveys and remote sensing we show that the erupted material was 4.8±1.2·1011 kg (benmoreite and trachyte, dense rock equivalent volume 0.18±0.05 km3). About 20% was lava and water-transported tephra, 80% was airborne tephra (bulk volume 0.27 km3) transported by 3–10 km high plumes. The airborne tephra was mostly fine ash (diameter <1000 µm). At least 7·1010 kg (70 Tg) was very fine ash (<28 µm), several times more than previously estimated via satellite retrievals. About 50% of the tephra fell in Iceland with the remainder carried towards south and east, detected over ~7 million km2 in Europe and the North Atlantic. Of order 1010 kg (2%) are considered to have been transported longer than 600–700 km with <108 kg (<0.02%) reaching mainland Europe.

THE GREENLAND FLOW DISTORTION EXPERIMENT

Greenland has a major influence on the atmospheric circulation of the North Atlantic-western European region, dictating the location and strength of mesoscale weather systems around the coastal seas of Greenland and directly influencing synoptic-scale weather systems both locally and downstream over Europe. High winds associated with the local weather systems can induce large air-sea fluxes of heat, moisture, and momentum in a region that is critical to the overturning of the thermohaline circulation, and thus play a key role in controlling the coupled atmosphere-ocean climate system. The Greenland Flow Distortion Experiment (GFDex) is investigating the role of Greenland in defining the structure and predictability of both local and downstream weather systems through a program of aircraft-based observation and numerical modeling. The GFDex observational program is centered upon an aircraft-based field campaign in February and March 2007, at the dawn of the International Polar Year. Twelve missions were fl...

A Climatology of Wintertime Barrier Winds off Southeast Greenland

A climatology of barrier winds along the southeastern coast of Greenland is presented based on 20 yr of winter months (1989‐2008) from the ECMWF Interim Reanalysis (ERA-Interim). Barrier wind events occur predominantly at two locations: Denmark Strait North (DSN; 67.78N, 25.38W) and Denmark Strait South (DSS; 64.98N, 35.98W). Events stronger than 20 m s 21 occur on average once per week during winter with considerable interannual variability—from 7 to 20 events per winter. The monthly frequency of barrier wind events correlates with the monthly North Atlantic oscillation (NAO) index with a correlation coefficient of 0.57 (0.31) at DSN (DSS). The associated total turbulent heat fluxes for barrier wind events (area averaged) were typically about 200 W m 22 with peak values of 400 W m 22 common in smaller regions. Area-averaged surface stresses were typically between 0.5 and 1 N m 22 . Total precipitation rates were larger at DSS than DSN, both typically less than 1 mm h 21 . The total turbulent heat fluxes were shown to have a large range as a result of a large range in 2-m air temperature. Two classes of barrier winds—warm and cold—were investigated and found to develop in different synoptic-scale situations. Warm barrier winds developed when there was a blocking high pressure over the Nordic seas, while cold barrier winds owed their presence to a train of cyclones channeling through the region.

Meteorological buoy observations from the central Iceland Sea

We present the first continuous in situ atmospheric observations from the central Iceland Sea collected from a meteorological buoy deployed for a 2 year period between 23 November 2007 and 21 August 2009. We use these observations to evaluate the ERA-Interim reanalysis product and demonstrate that it represented low-level meteorological fields and surface turbulent fluxes in this region very well. The buoy observations showed that moderate to strong winds were common from any direction, while wind speeds below 5 ms−1 were relatively rare. The observed low-level air temperature and surface heat fluxes were related to the wind direction with cold-air outbreaks most common from the northwest. Mean wintertime turbulent heat fluxes were modest (<60 Wm−2), but the range was substantial. High heat flux events, greater than 200 Wm−2, typically occurred every 1–2 weeks in the winter, with each event lasting on average 2.5 days with an average total turbulent heat flux of ∼200 Wm−2 out of the ocean. The most pronounced high heat flux events over the central Iceland Sea were associated with cold-air outbreaks from the north and west forced by a deep Lofoten Low over the Norwegian Sea.

Comparison of the ocean surface vector winds from atmospheric reanalysis and scatterometer-based wind products over the Nordic Seas and the northern North Atlantic and their application for ocean modeling

Ocean surface vector wind fields from reanalysis data sets and scatterometer-derived gridded products are analyzed over the Nordic Seas and the northern North Atlantic for the time period from 2000 to 2009. The data sets include the National Center for Environmental Prediction Reanalysis 2 (NCEPR2), Climate Forecast System Reanalysis (CFSR), Arctic System Reanalysis (ASR), Cross-Calibrated Multiplatform (CCMP) wind product version 1.1 and recently released version 2.0, and QuikSCAT. The goal of the study is to assess discrepancies across the wind vector fields in the data sets and demonstrate possible implications of these differences for ocean modeling. Large-scale and mesoscale characteristics of winds are compared at interannual, seasonal, and synoptic timescales. A cyclone tracking methodology is developed and applied to the wind fields to compare cyclone characteristics in the data sets. Additionally, the winds are evaluated against observations collected from meteorological buoys deployed in the Iceland and Irminger Seas. The agreement among the wind fields is better for longer time and larger spatial scales. The discrepancies are clearly apparent for synoptic timescales and mesoscales. CCMP, ASR, and CFSR show the closest overall agreement with each other. Substantial biases are found in the NCEPR2 winds. Numerical sensitivity experiments are conducted with a coupled ice-ocean model forced by different wind fields. The experiments demonstrate differences in the net surface heat fluxes during storms. In the experiment forced by NCEPR2 winds, there are discrepancies in the large-scale wind-driven ocean dynamics compared to the other experiments.

Mapping Offshore Winds Around Iceland Using Satellite Synthetic Aperture Radar and Mesoscale Model Simulations

The offshore wind climate in Iceland is examined based on satellite synthetic aperture radar (SAR), coastal meteorological station measurements, and results from two atmospheric model data sets, HARMONIE and NORA10. The offshore winds in Iceland are highly influenced by the rugged coastline. Lee effects, gap flow, coastal barrier jets, and atmospheric gravity waves are not only observed in SAR, but are also modeled well from HARMONIE. Offshore meteorological observations are not available, but wind speed and wind direction measurements from coastal meteorological masts are found to compare well to nearby offshore locations observed by SAR. More than 2500 SAR scenes from the Envisat ASAR wide swath mode are used for wind energy resource estimation. The wind energy potential observed from satellite SAR shows high values above

Observations of the altitude of the volcanic plume during the eruption of Eyjafjallajökull, April–May 2010

{1000}\;{Wm}^{ - {2}}

The impact of the atmosphere on the Eyjafjallajökull 2010 eruption plume

in coastal regions in the south, east, and west, with lower values in the north. The most promising region for wind energy production is the southwestern coastal region.