Quarterly Journal of the Royal Meteorological Society
Q. J. R. Meteorol. Soc. 137: 1657–1658, October 2011 A
Editorial
IPY-THORPEX
Jón Egill Kristjánssona * and Erik W. Kolstadb
a
b
University of Oslo, Norway
Bjerknes Centre for Climate Research, Bergen, Norway
*Correspondence to: J. E. Kristjánsson, University of Oslo, Department of Geosciences, P.O.Box 1022, Blindern, Oslo,
0315, Norway. E-mail: jegill@geo.uio.no
DOI:10.1002/qj.965
The fourth International Polar Year (IPY) of 2007–2009 fostered broad international collaboration to address scientific
challenges in the polar regions. Among these challenges are those related to weather phenomena and weather prediction
in the harsh, remote, data-sparse high latitudes.
Small-scale, unexpected severe weather events are well-documented in Norwegian historical sources. The poet and priest
Petter Dass (1647–1707) wrote about how fishing villages along the coast of northern Norway were devastated when most
of the male population perished in the same storms. Often, the fishermen would go out to sea when the weather cleared
after days of strong, mild southerly winds, only to be surprised by what were most likely polar lows or Arctic fronts from
the north. Similarly, the historian Eilert Sundt wrote about drownings along the entire Norwegian coast around 1850, and
found that although the population was lower in the northern (Arctic) regions, the number of casualties at sea far exceeded
those further south.
Objective measures of NWP forecast skill indicate that the largest forecast errors in the North Atlantic are found
north of the Arctic circle (e.g., Jung and Leutbecher, 2007). To meet some of the challenges associated with forecasting
and understanding mesoscale Arctic weather phenomena a cluster of projects, termed IPY-THORPEX, was formed,
linking directly to The Observing System Research and Predictability Experiment (THORPEX) programme of the World
Meteorological Organization (WMO). The IPY-THORPEX cluster, led from Norway, consisted of ten individual IPY
projects from nine countries with the overall objective of improving forecasting of high impact weather in the polar
regions. In order to achieve these objectives, better exploitation of satellite data and other observations was targeted, as
well as efforts to improve our understanding of physical and dynamical processes in the polar atmosphere.
One of the projects of the IPY-THORPEX cluster was the Greenland Flow Distortion experiment (GFDex), which was
described in a special issue of the Quarterly Journal of the Royal Meteorological Society in 2009. In the current issue, we
describe another project of the cluster, ‘‘IPY-THORPEX: improved forecasting of adverse weather in the Arctic – present
and future’’, hereafter called IPY-THORPEX for brevity. The project was funded by the Norwegian Research Council
through its IPY programme and dealt with three types of Arctic weather phenomena; polar lows, Arctic fronts and
orographic wind storms in stable Arctic air masses. These mesoscale weather phenomena have in common that they are
poorly captured by the conventional observational network and there are significant gaps in our understanding of them.
Among these three phenomena, there was a special focus on polar lows in the project.
Polar lows form in marine cold air outbreaks during the winter (Kolstad et al., 2009), when very high turbulent fluxes
from the sea to the atmosphere occur. In addition to the intense convection that takes place, they almost invariably form in
a baroclinic environment, and the interplay between low-level baroclinicity, upper-level potential vorticity (PV) forcing,
latent heat release and sensible heat fluxes is not well understood.
The most ambitious part of the IPY-THORPEX project was a 3-week aircraft-based measurement campaign in FebruaryMarch 2008 (Kristjánsson et al., 2011). The campaign was carried out in collaboration with the German Aerospace Centre
(DLR), with their Falcon-20 aircraft, combining traditional dropsonde releases and in situ turbulence measurements with
remotely sensing humidity and wind LIDAR systems (Wagner et al., 2011). Further support for the campaign was obtained
from EUFAR, the Norwegian Coast Guard and the Norwegian Meteorological Institute.
A major achievement of the 2008 campaign was the capture – at three different stages of development – of a vigorous
polar low over the Norwegian Sea on 3–4 March, providing a unique data set for step-by-step validation of NWP models
during a polar low development. The paper by Føre et al. presents an analysis of the data from the 55 dropsondes of those
three flights, combined with satellite imagery and PV inversions. This is followed by a paper by McInnes et al., in which
the ability to simulate the polar low at different horizontal resolutions is explored. The Irvine et al. study explores the
conceivable benefit of additional observations by targeting flights into ‘sensitive’ areas, following up on a related study
during the GFDex campaign (Irvine et al., 2009). The study by Randriamampianina et al. assesses the potential of closing
the observational gap in the Arctic by exploiting new satellite data (IASI) with high spectral and vertical resolution.
c 2011 Royal Meteorological Society
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J. E. Kristjánsson and E. W. Kolstad
The study by Adakudlu and Barstad deals with another polar low that was captured by a flight on 1 March. Using
the campaign data for verification, they performed numerical simulations to investigate the sensitivity of the polar low
evolution to varying sea surface temperatures. The final campaign-based study in this issue is the paper by Barstad and
Adakudlu, which deals with gap flow and wake formation induced by the orography of Svalbard. This is followed by a
study by Reeve and Kolstad of tip jets near the southern tip of Spitsbergen, the largest island in the Svalbard archipelago.
We then present a climatology of polar lows by Kolstad, who, recognizing the inability of climate models to resolve polar
lows, defined a simple parameter-based index or proxy for polar lows, with possible applications in climatological studies
and weather forecasting. This is followed by an updated climatology of polar lows in the Nordic Seas by Noer et al., based
on infrared satellite images for the years 2000–2009.
The final two studies of this volume deal with polar low case studies in the Nordic Seas. Kristjánsson et al. describe a
polar low northwest of Iceland, for which they find evidence for a strong influence of flow distortion from East Greenland’s
orography. Nordeng and Røsting investigate an intense polar low that struck the coast of Northern Norway in November
2008.
In a warming climate, the frequency and preferred locations of polar lows may change (Kolstad and Bracegirdle, 2008).
Increasing human activities with decreasing sea ice in the Arctic may then encounter polar lows in areas further north than
before, highlighting the societal importance of the type of research presented here.
We are very grateful to the Quarterly Journal for publishing this special issue. In addition to being a highly respected
and widely read journal, it has published several key papers on mesoscale weather phenomena, including the early polar
low papers of Duncan (1977) and Rasmussen (1979). It has been a great pleasure to work with the editors and staff of the
Quarterly Journal and Wiley, especially John Thuburn, Georgina Lea, Alison Hunter and Timothy Roberts.
References
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Irvine EA, Gray SL, Methven J, Renfrew IA, Bovis K, Swinbank R. 2009. The impact of targeted observations made during the Greenland Flow
Distortion Experiment. Q. J. R. Meteorol. Soc. 135: 2012–2029.
Jung T, Leutbecher M. 2007. Performance of the ECMWF forecasting system in the Arctic during winter. Q. J. R. Meteorol. Soc 133: 1327–1340.
Kolstad EW, Bracegirdle TJ. 2008. Marine cold air outbreaks in the future: an assessment of IPCC AR4 model results for the Northern Hemisphere.
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Kolstad EW, Bracegirdle TJ, Seierstad IA. 2009. Marine cold-air outbreaks in the North Atlantic: temporal distribution and associations with
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Kristjánsson JE, Barstad I, Aspelien T, Føre I, Hov Ø, Irvine E, Iversen T, Kolstad E, Nordeng TE, McInnes H, Randriamampianina R, Sætra Ø,
Shapiro M, Spengler T, Ólafsson H. 2011. The Norwegian IPY-THORPEX: Polar Lows and Arctic Fronts during the 2008 Andøya campaign.
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c 2011 Royal Meteorological Society
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