Abstract We use Columbia Glacier as a case study to demonstrate how seismically cataloged calving events in Alaska can track glacier evolution over two decades. By combining this catalog—a serendipitous byproduct of earthquake monitoring—with terminus positions, bathymetry, glacier thickness, surface velocity, and environmental records, we show how this seismicity responds to changes in the glacier. We find that fjord bathymetry at the terminus is a strong control on seismicity. As the glacier recedes into shallow water, the number of glacier quakes increases due to the transition to grounded conditions, which favor serac failure. We find evidence that glacier speed, precipitation, and warm ocean temperatures raise the rate of cataloged glacier quakes. We also observe that the energy of individual quakes increases with the elevation of the terminus. Our results highlight potential future uses of the cataloged calving record in Alaska that spans more than a dozen other glacier systems.

Alaska is a unique US state because of its large size, geographically disparate population density, and physical distance from the contiguous United States. Here, we describe a pattern of SARS-CoV-2 variant emergence across Alaska reflective of these differences. Using genomic data, we found that in Alaska, the Omicron sublineage BA.2.3 overtook BA.1.1 by the week of 27 February 2022, reaching 48.5% of sequenced cases. On the contrary, in the contiguous United States, BA.1.1 dominated cases for longer, eventually being displaced by BA.2 sublineages other than BA.2.3. BA.2.3 only reached a prevalence of 10.9% in the contiguous United States. Using phylogenetics, we found evidence of potential origins of the two major clades of BA.2.3 in Alaska and with logistic regression estimated how it emerged and spread throughout the state. The combined evidence is suggestive of founder events in Alaska and is reflective of how Alaska’s unique dynamics influence the emergence of SARS-CoV-2 variants.

While recent increases in heavy precipitation events in some midlatitude regions are consistent with climate model simulations, evidence of such increases in high latitudes is more tenuous, partly because of data limitations. The present study evaluates historical and future changes in extreme precipitation events in Alaska. Using the ERA5 reanalysis, station data, and output from two downscaled global climate models, we examine precipitation-driven flood events at five diverse locations in Alaska where major historical floods provide benchmarks: Fairbanks (August 1967), Seward (October 1986), Allakaket/Bettles (August 1994), Kivalina (August 2012), and Haines (December 2020). We place these precipitation events into a framework of historical trends and end-of-century (2065–2100) model projections. In all but one of the flood events, the amount of rainfall was the highest on record for the event duration, and precipitation events of this magnitude are generally projected by the models to remain infrequent. All of the cases had subtropical or tropical moisture sources. None of the locations show statistically significant historical trends in the magnitude of extreme precipitation events. However, the frequencies of heavy precipitation events are projected to increase at most of the locations. The frequency of events with 2 year and 5 year historical return intervals is projected to become more frequent, especially in the Interior, and in some cases increase to several times per year. Decreases are projected only for Seward along Alaska’s southern coast.

Abstract We analyze physical processes leading to daily wintertime (December, January, and February) extreme precipitation events in Alaska between 1986 and 2005. This is done by applying self‐organizing maps to environmental conditions corresponding to National Centers for Environmental Information precipitation, using the European Centre for Medium‐Range Weather Forecasts reanalysis (ERA‐Interim) and Coupled Model Intercomparison Project 5 (CMIP5) global climate selected Global climate model (GCM; selected GCMs). We focus on widespread extreme events, defined as the top 0.1% of daily precipitation occurring on at least six grid boxes on the same day. The self‐organizing maps methodology allows identifying large‐scale circulations conducive to extreme events. This methodology identifies distinctive circulation patterns conducive to producing extreme events with a trough west of Alaska leading to south or southwest flow across the state. Extreme events occur along the windward (southern) side of the Alaska Range due to uplift by the mountains in the ERA‐Interim and in all models. In the National Centers for Environmental Information observations, precipitation rates are greater than in any of the selected GCMs. Simulated extreme precipitation decreases as model resolution decreases, and our study suggests that the smoothness of model topography is a reason for the scaling between model precipitation rate and model resolution.

Abstract Rain-on-snow (ROS) events can have adverse impacts on high-latitude ungulate populations when rain freezes in the snowpack, forming ice layers that block access to winter forage. In extreme cases, ROS events have led to mass die-offs. ROS events are linked to advection of warm and moist air, associated with extratropical cyclones. However, these conditions are common to many winter precipitation events, challenging our understanding of the particular conditions under which ROS events occur. This study uses the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) to differentiate ROS events in Alaska from precipitation events in which only snow falls on a preexisting snowpack [snow-on-snow (SOS)]. Over the North Slope and Kotzebue Sound, no clear difference exists between the tracks of ROS-producing and SOS-producing storms. However, in the interior, southwest, and Anchorage, tracks of ROS-producing storms tend to be farther north and west than for SOS-producing storms. The northwest shift of ROS-producing storms is linked to the position of upper-tropospheric anticyclones in the eastern Gulf of Alaska during ROS events. ROS-producing storms are no more intense than SOS-producing storms, but their association with atmospheric blocking leads to stronger pressure gradients on the east side of storms and thereby stronger advection of positive anomalies in temperature and precipitable water. For several sites, sea level pressure in the eastern Gulf of Alaska is also significantly higher a few days prior to ROS events than prior to SOS events, further implicating atmospheric blocking as a facilitator and potential predictor of ROS events.

Synoptic‐scale patterns associated with daily temperature and precipitation extremes in Alaska are identified and evaluated for daily variability in order to understand consistency in forcing mechanisms associated with extreme events as well as the tendency for each pattern to produce an extreme event. Daily station data at five locations for the 29‐year period from 1982 to 2010 are used. The widely recognized ClimDex indices are used to identify extreme high temperature, low temperature, and single‐day precipitation events. Pressure patterns during extreme events are evaluated seasonally for summer (JJA) and winter (DJF) at mean sea level pressure, 700 and 500‐hPa geopotential heights. Temperature extremes are largely characterized by synoptic‐scale patterns associated with substantial warm and cold air advection, and precipitation extremes are associated with moisture advection from the North Pacific. Extreme warm and cold temperature events are generally associated with more consistent daily synoptic‐scale patterns than precipitation. Considerable dissimilarities among daily synoptic‐scale patterns associated with extreme events based on location, type of extreme event and season highlight the need for careful consideration in the practice of applying synoptic‐scale forcing patterns to forecast or downscale extreme weather events in Alaska.

Environmental factors influencing the distribution and abundance of Alexandrium catenella in Kachemak bay and lower cook inlet, Alaska

Wet snow and the icing events that frequently follow wintertime rain-on-snow (ROS) affect high latitude ecosystems at multiple spatial and temporal scales, including hydrology, carbon cycle, wildlife, and human development. However, the distribution of ROS events and their response to climatic changes are uncertain. In this study, we quantified ROS spatiotemporal variability across Alaska during the cold season (November to March) and clarified the influence of precipitation and temperature variations on these patterns. A satellite-based daily ROS geospatial classification was derived for the region by combining remote sensing information from overlapping MODIS and AMSR sensor records. The ROS record extended over the recent satellite record (water years 2003–2011 and 2013–2016) and was derived at a daily time step and 6 km grid, benefiting from finer (500 m) resolution MODIS snow cover observations and coarser (12.5 km) AMSR microwave brightness temperature-based freeze–thaw retrievals. The classification showed favorable ROS detection accuracy (75%–100%) against in situ climate observations across Alaska. Pixel-wise correlation analysis was used to clarify relationships between the ROS patterns and underlying physiography and climatic influences. Our findings indicate that cold season ROS events are most common during autumn and spring months along the maritime Bering Sea coast and boreal interior regions, but are infrequent on the colder arctic North Slope. The frequency and extent of ROS events coincided with warm temperature anomalies (p < 0.1), but showed a generally weaker relationship with precipitation. The weaker precipitation relationship was attributed to several factors, including large uncertainty in cold season precipitation measurements, and the important contribution of humidity and turbulent energy transfer in driving snowmelt and icing events independent of rainfall. Our results suggest that as high latitude temperatures increase, wet snow and ROS events will also increase in frequency and extent, particularly in the southwestern and interior regions of Alaska.

High winds cause waves, storm surge, erosion and physical damage to infrastructure and ecosystems. However, there have been few evaluations of wind climatologies and future changes, especially change in high-wind events, on a regional basis. This study uses Alaska as a regional case study of climatological wind speed and direction. Eleven first-order stations across different subregions of Alaska provide historical data (1975-2005) for the observational climatology and for the calibration of Coupled Model Inter comparison Project (CMIP5) simulations, which in turn provide projections of changes in winds through 2100. Historically, winds exceeding 25 and 35 knots are most common in the Bering Sea coastal region of Alaska, followed by northern Alaska coastal areas. Autumn and winter are the seasons of most frequent high-wind occurrences in the coastal sites, while there is no distinct seasonal peak at the interior stations where high-wind events are less frequent. An examination of the sea level pressure pattern associated with the highest-wind event at each station reveals the presence of a strong pressure gradient associated with an extratropical cyclone in most cases. Northern coastal regions of Alaska are projected to experience increased frequencies of high-wind events during the cold season, especially late autumn and early winter, when reduced sea ice cover in the late century will leave coastal regions increasingly vulnerable to flooding and erosion.

Increasing temperatures have resulted in reduced growth and increased tree mortality across large areas of western North American forests. We use tree-ring isotope chronologies (δ13 C and δ18 O) from live and dead trees from four locations in south-central Alaska, USA, to test whether white spruce trees killed by recent spruce beetle (Dendroctonus rufipennis Kirby) outbreaks showed evidence of drought stress prior to death. Trees that were killed were more sensitive to spring/summer temperature and/or precipitation than trees that survived. At two of our sites, we found greater correlations between the δ13 C and δ18 O chronologies and spring/summer temperatures in dead trees than in live trees, suggesting that trees that are more sensitive to temperature-induced drought stress are more likely to be killed. At one site, the difference between δ13 C in live and dead trees was related to winter/spring precipitation, with dead trees showing stronger correlations between δ13 C and precipitation, again suggesting increased water stress in dead trees. At all sites where δ18 O was measured, δ18 O chronologies showed the greatest difference in climate response between live and dead groups, with δ18 O in live trees correlating more strongly with late winter precipitation than dead trees. Our results indicate that sites where trees are already sensitive to warm or dry early growing-season conditions experienced the most beetle-kill, which has important implications for forecasting future mortality events in Alaska.

Extreme temperature and precipitation events in Alaska are examined in an ensemble of global climate models (GCMs) and an atmospheric reanalysis. Extreme monthly maximum and minimum temperature and the monthly maximum 5-day precipitation amount are evaluated for a 30-year historical period and two 30-year future time slices (2050s and 2080s). Although biases exist, models capture the spatial pattern and seasonality of the extremes depicted by the ERA-40 reanalysis. Discrepancies between station data (Anchorage, Fairbanks and Barrow) and GCMs/reanalysis are larger than the model-reanalysis differences, and are consistent with (1) surface elevation differences arising from the models' resolution and (2) gauge undercatch of precipitation in the station data. GCMs project future changes that are 2–4 times larger than the across-model standard deviations. The largest changes projected by the GCMs are significantly different from the historical mean at the 95% confidence level. Changes in extreme minimum temperature and extreme 5-day precipitation projections are larger than changes in means. The extreme minimum temperatures are projected to increase 2–3 times as much as the extreme maximum temperatures in all seasons except summer, with the largest increases of extreme minima in coastal regions. By the 2080s, the increases in all three extremes indices are twice as large in the Representative Concentration Pathway (RCP) 8.5 as in the RCP 4.5 scenario. The magnitude of the projected increase of maximum 5-day precipitation is largest in southern and inland areas, although the percentage increase is largest in the north. In the RCP 8.5 simulations, the inter-annual variability of extreme temperatures narrows by the end of the century, most notably in autumn. Record-breaking 5-day precipitation events become more common in the RCP 8.5 than in the RCP 4.5 scenario.

Climate change has contributed to increasing temperatures, earlier snowmelts and thinning ice packs in the Arctic, where crossing frozen bodies of water is essential for transportation and subsistence living. In some Arctic communities, anecdotal reports indicate a growing belief that falling-through-the-ice (FTI) are increasing. The objective of this study was to describe the morbidity and mortality associated with unintentional FTIs in Alaska. We searched newspaper reports to identify FTI events from 1990 to 2010. We also used data from a trauma registry, occupational health and law enforcement registries and vital statistics to supplement the newspaper reports. Morbidity and mortality rates were calculated for Alaska Native (AN) people and all Alaskans. During the 21-year period, we identified 307 events, affecting at least 449 people. Events ranged from no morbidity to fatalities of five people. More than half of the events involved transportation by snow machine. Mortality rates were markedly higher for AN people than that for all Alaskans. We provide a numeric estimate of the importance of FTI events in Alaska. FTIs may represent an adverse health outcome related to climate changes in the Arctic, and may be particularly critical for vulnerable populations such as AN people.

Creation of ice layers in snow due to thaw-refreeze events can lock away winter forage, preventing access by large mammals and causing population declines. Data are limited, however, on the frequency, timing, extent, and size of thaw-refreeze events in northern latitudes given the area’s remoteness and paucity of weather stations. We used a remote sensing approach to detect thaw-refreeze events in Alaska during winter between 2001 and 2008. We also compared these results to a regional climate reanalysis dataset that identified rain events (freezing and non-freezing rain). All areas of the state, except high elevation sites, had ≥1 thaw-refreeze event during the study period. Southwestern Alaska had the highest frequency of thaw-refreeze events with an average of >4 events each winter, whereas northern Alaska had the lowest frequency with an average of <2 events. We observed substantial inter-annual variation in the distribution and frequency of thaw-refreeze events. For most of the state, thaw-refreeze occurred at similar rates each winter month, except in northern Alaska where thaw-refreeze events were most frequent in early and later winter. The median extent of individual thaw-refreeze events was 469 km2, however, events in the interior of the state tended to be larger. Remotely sensed thaw-refreeze detections generally had low correspondence with observations from the climate reanalysis dataset. Our results support the use of remotely sensed data to identify thaw-refreeze events.

We detected a slow slip event in the south central Alaska Subduction Zone by analyzing continuous GPS data from the Plate Boundary Observatory (PBO) network. The slow slip event started in early 2010 at a depth of 35 km beneath the Cook Inlet, near the down‐dip end of the locked zone, and is ongoing as of November 2011 with an accumulated magnitude ofMw 6.9. Analysis of the earthquake catalog in the same area using the stochastic Epidemic Type Aftershock Sequence model (ETAS) shows a small but detectable seismicity increase during the slow slip event. We also find a change in seismicity rate around 1998, that may suggest an earlier slow slip event in the same region. Slow slip events in Alaska appear more widespread than previously thought but have remained undetected due to their long durations, the time intervals between them, and the limited time records from the continuous GPS.

ABSTRACT The NOAA Emergency Response Division (ERD aka Hazmat) provides a complete set of scientific assistance and support to the U.S. Coast Guard in response to an offshore oil spill. Historically NOAA National Weather Service (NWS) has provided the operational weather support component for ERD in the form of forecasts and observations. The dearth of conventional weather data in remote locations provide unique challenges for providing weather support for Hazmat events in locations such as the Aleutian Island Chain of Alaska. Weather support for Hazmat events in Alaska are further complicated during the storm season from October through March due to the frequency and intensity of storms in Alaska combined with the vast distances to reach the scene. Such was the case when the M/V Selendang Ayu grounded on Unalaska Island in the Aleutian Islands, 800 miles southwest of Anchorage, within the AOR of NWS Weather Forecast Office Anchorage. Unalaska Island has a handful of permanent observational platforms, all in the vicinity of Dutch Harbor. However, the M/V Selendang Ayu was foundering on the west side of the island, in a different meteorological and oceanographic regime. WFO Anchorage developed a plan that included siting a land-based weather station near the wreck, a specialized processing of Synthetic Aperture Radar Satellite (SARSat) passes, and a Selendang Ayu event web portal populated with tailored products for the event within 24 hours. Given the significance of the event within a highly vulnerable ecosystem, one of the first actions that the ERD Alaska Scientific Support Coordinator initiated was to exercise an agreement with the NWS to bring their Incident Meteorologist on scene as part of the NOAA Scientific Support Team. The NWS response was immediate and effective. Within a week the first Incident Meteorologist (IM) was on scene providing regional and localized weather reviews and forecasts for the IC Post as well as weather briefings on request for helo pilots and boat skippers. On scene IM support continued for the next two months. Weather support through the spring and summer was provided via phone and web by the Anchorage Forecast Office.

Survival of immersions during recreational boating events in Alaska, 1999–2004

This section summarizes downstream developments of the previous month. Exploration &amp; Production are covered in 'Upstream Review'. Crude oil prices rose on news that BP was to shut‐in its 400,000 bpd Prudhoe Bay field, following the discovery of corrosion in a pipeline serving the field. Dated BFO went to a record high of $78.72/bbl on 8th August. Speculation that refiners on the US West Coast would seek to replace the lost Alaska North Slope crude with supplies from the Asia/Pacific region caused prices to rise there as well. US crude prices were rather less affected than elsewhere by events in Alaska as it rapidly became clear that stock levels were sufficient to deal with any loss of production. It also emerged that BP was able to keep about half of Prudhoe Bay in production. By that time, however, oil markets had latched on to an entirely different source of worry. The announcement in London that police had uncovered a plot to blow‐up aeroplanes crossing the Atlantic led to concerns of a sharp fall in passenger travel. Traders were not simply worried about the effect of this on the demand for jet fuel, but expressed concerns of a more general loss of business confidence across the world. Fears over a fall in jet fuel consumption did not appear to have spread to Singapore, where jet kerosine traded at an all‐time high of $91.75/bbl early in August.

Hospitalizations for immersion-related injuries in Alaska 1991–2000

Xylem embolism was measured in nine tree species for one or more years. Species were ring—porous (Quercus sp.), diffuse—porous (Alnus, Betula, Populus spp.) or coniferous (Picea, Larix, Abies spp.). Intraspecific (Populus tremuloides) and intrageneric (Betula, Alnus) comparisons were made between sites in northern Utah and interior Alaska. Most embolism, &gt;90% in some dicot species, occurred in winter. Within sites, dicot trees embolized more than conifers. Between sites, Alaskan dicot trees embolized less than their Utah counterparts. Differences were explained by vulnerability to embolism caused by freeze—thaw cycles. Most conifers were entirely resistant, whereas dicot trees were vulnerable. Less embolism in Alaskan dicot trees was associated with fewer freeze—thaw events in Alaska vs. Utah. Vulnerability was positively correlated with conduit volume and hydraulic conductance per unit xylem area (ks). Tracheids were superior to vessels in avoiding freeze—thaw—induced embolism, and had lower ks. At the other extreme, ring—porous xylem had the highest ks but lost &gt;90% of hydraulic conductance after a single freeze—thaw event. Vulnerability to water—stress—induced cavitation was not correlated with conduit volume or ks. Dicot species either reversed winter embolism by refilling vessels with positive root pressures during spring (Betula, Alnus spp.), or tolerated it and relied on new xylem production to restore hydraulic conductance (Quercus sp.). Conifers reversed embolism by refilling tracheids in the absence of positive pressure. Populus species behaved inconsistently, showing some reversal one year but none the next. Even without embolism reversal, Populus species had hydraulic conductances per unit leaf area equal to other diffuse—porous species.