The Arctic is becoming more accessible as sea ice extent continues to decline, resulting in higher human exposure to Arctic storms. This study compares Arctic storm characteristics between the ECMWF-Interim Reanalysis, 55-year Japanese Reanalysis, NASA-Modern Era Retrospective Analysis for Research and Applications Version 2 and National Centre for Environmental Prediction-Climate Forecast System Reanalysis datasets between 1980 and 2017, in winter (DJF) and summer (JJA). It is shown that Arctic storm characteristics are sensitive to the variable used for storm tracking. Arctic storm frequency is found to be similar in summer and winter when using sea level pressure minima to track Arctic storms, whereas, the storm frequency is found to be higher in winter than summer when using 850 hPa relative vorticity to track storms, based on using the same storm tracking algorithm. It is also found that there are no significant trends in Arctic storm characteristics between 1980 and 2017. Given the sparsity of observations in the Arctic, it might be expected that there are large differences in Arctic storm characteristics between the reanalysis datasets. Though, some similar Arctic storm characteristics are found between the reanalysis datasets, it is found that the differences in Arctic storm characteristics between the reanalysis datasets are generally higher in winter than in summer. Overall, the results show that there are differences in Arctic storm characteristics between reanalysis datasets, but even larger differences can arise between using 850 hPa relative vorticity or mean sea level pressure as the storm tracking variable, which adds to the uncertainty associated with current Arctic storm characteristics.

<p>Arctic sea ice has reduced significantly over recent decades and is projected to reduce further over this century. This has made the Arctic more accessible and increased opportunities for the expansion of business and industrial activities.  As a result, the exposure and risk of humans and infrastructure to extreme storms will increase in the Arctic.</p><p>Our understanding of the current risk from storms comes from analysing the past, for example, by using storm tracking algorithms to detect storms in reanalysis datasets.  However, there are multiple reanalysis datasets available from different institutions and there are multiple storm tracking methods.  Previous studies have found that there can be differences between reanalysis datasets and between storm tracking methods in the climatology of storms, particularly in mid-latitude regions rather than the Arctic.  In this study, we aimed to improve the understanding of Arctic storms by assessing their characteristics in multiple global reanalyses, the ECMWF-Interim Reanalysis (ERA-Interim), the 55-Year Japanese Reanalysis (JRA-55), the NASA-Modern Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2), and the NCEP-Climate Forecast System Reanalysis (NCEP-CFSR), using the same storm tracking method based on 850 hPa relative vorticity and mean sea level pressure.</p><p>The results from this study show that there are no significant trends in Arctic storm characteristics between 1980-2017, even though the Arctic has undergone rapid change.  Although some similar Arctic storm characteristics are found between the reanalysis datasets, there are generally higher differences between the reanalyses in winter (DJF) than in summer (JJA).  In addition, substantial differences can arise between using the same storm tracking method based on 850 hPa relative vorticity or mean sea level pressure, which adds to the uncertainty associated with current Arctic storm characteristics.</p>

Abstract. Understanding the location and intensity of hazardous weather across the Arctic is important for assessing risks to infrastructure, shipping, and coastal communities. Key hazards driving these risks are extreme near-surface winds, high ocean waves, and heavy precipitation, which are dependent on the structure and development of intense synoptic-scale cyclones. This study aims to describe the typical lifetime, structure, and development of a large sample of past intense winter (DJF) and summer (JJA) synoptic-scale Arctic cyclones using a storm compositing methodology applied to the ERA5 reanalysis. Results show that the composite development and structure of intense summer Arctic cyclones are different from those of intense winter Arctic and North Atlantic Ocean extra-tropical cyclones and from those described in conceptual models of extra-tropical and Arctic cyclones. The composite structure of intense summer Arctic cyclones shows that they typically undergo a structural transition around the time of maximum intensity from having a baroclinic structure to an axi-symmetric cold-core structure throughout the troposphere, with a low-lying tropopause and large positive temperature anomaly in the lower stratosphere. Summer Arctic cyclones are also found to have longer lifetimes than winter Arctic and North Atlantic Ocean extra-tropical cyclones, potentially causing prolonged hazardous and disruptive weather conditions in the Arctic.

Abstract. Understanding the location and intensity of hazardous weather across the Arctic is important for assessing risks to infrastructure, shipping, and coastal communities. A key driver of these risks are the high winds, high ocean waves and heavy precipitation, which are dependent on the structure and development of intense synoptic-scale cyclones. This study aims to describe the typical lifetime, structure, and development of a large sample of past intense winter (DJF) and summer (JJA) synoptic-scale Arctic cyclones, using a storm compositing methodology applied to the ERA5 reanalysis. Results show that the composite development and structure of intense Arctic summer cyclones is different to that of intense winter Arctic and North Atlantic Ocean extra-tropical cyclones, and to that described in conceptual models of extra-tropical and Arctic cyclones. The composite structure of intense Arctic summer cyclones shows that they typically undergo a structural transition around the time of maximum intensity from having a baroclinic structure to an axi-symmetric cold-core structure throughout the troposphere, with a low-lying tropopause and large positive temperature anomaly in the lower stratosphere. Arctic summer cyclones are also found to have longer lifetimes than these other cyclones, potentially causing prolonged hazardous and disruptive weather conditions in the Arctic.

<p>The Arctic has undergone significant change over the past few decades, and there has been great reductions in Arctic sea ice extent. The Arctic ocean has become more accessible, and this has allowed for more human activity in the Arctic.  The risk of storms impacting human activities in the Arctic has consequently increased, and as sea ice extent continues to decline in the near-future, the risk of storms impacting human activities in the Arctic is likely to increase further.  In this study, the present climatology of Arctic storms is evaluated between modern reanalysis datasets, and the future climatology of Arctic storms is also evaluated in climate model simulations.</p><p>There are multiple reanalysis datasets available from different institutions, which each give an approximation of past atmospheric conditions over the last few decades.  In addition, there are multiple storm tracking methods, which may impact the climatology of Arctic storms that is identified in a reanalysis datasets.  In this study, we aimed to improve the understanding of Arctic storms by assessing their characteristics in multiple global reanalyses, the ECMWF-Interim Reanalysis (ERA-Interim), the 55-Year Japanese Reanalysis (JRA-55), the NASA-Modern Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2), and the NCEP-Climate Forecast System Reanalysis (NCEP-CFSR), using the same storm tracking method based on 850 hPa relative vorticity and mean sea level pressure.  In addition, the response of Arctic storms to climate change has been evaluated in the UPSCALE climate simulations, and the affect of horizontal resolution on the representation of future Arctic storminess has been assessed.</p><p>The results show that there are no significant trends in Arctic storm characteristics between 1980-2017, even though the Arctic has undergone rapid change.  Although some similar Arctic storm characteristics are found between the reanalysis datasets, there are generally higher differences between the reanalyses in winter (DJF) than in summer (JJA).  In addition, substantial differences can arise between using the same storm tracking method based on 850 hPa relative vorticity or mean sea level pressure, which adds to the uncertainty associated with current Arctic storm characteristics.</p><p>The results also show that Arctic storms will change significantly in a future climate, particularly in their spatial distribution.  Differences have been found between the future simulations of Arctic storms between an ensemble of high resolution climate models (25km) and low resolution climate models (130km), which adds uncertainty to how Arctic storms may change in a future climate.  The possible reasons for why the representation of future climate Arctic storms may be different in climate models of differing horizontal resolution has been explored.</p>