Climatology of Barrier Jets along the Alaskan Coast. Part II: Large-Scale and Sounding Composites

This paper investigates the large-scale flow and thermodynamic structures associated with barrier jets along the Alaskan coast using the National Centers for Environmental Prediction (NCEP) reanalysis, as well as the average wind, moisture, and thermodynamic soundings at Yakutat, Alaska (YAK), and Whitehorse, Yukon Territory, Canada (YXY). Large-scale and sounding composites are constructed for all barrier jets objectively identified around YAK using synthetic aperture radar (SAR) imagery during the cool and warm seasons of 1998–2003. During the cool season the jet events are separated into those with sharp upstream wind gradients (shock jets), highly variable (“gustlike”) surface winds (variable jets), and the other jet events (other jets). Those cool season barrier jets without shock or variable characteristics are associated with an anomalously deep upper-level trough approaching the Gulf of Alaska and an anomalous ridge over western Canada and interior Alaska. The associated surface cyclone and surface ridging result in strong low-level southerlies over southeast Alaska and the advection of 850-mb warm anomalies northward from the subtropics to Alaska. In contrast, the shock events have significant cold anomalies at 850 mb over the interior, while both the shock and variable jets have less upper-level ridging over the interior. The warm season other-jet composite is similar to that for the cool season, except that an 850-mb cool anomaly develops near the coast and the approaching upper-level trough is not significantly deeper than climatology. The sounding composite at YAK of the other-jet type during the cool season is more stable, moist, and slightly cooler at lower levels than the nonjet events. The largest low-level cool, dry, and high stability anomalies are for the shock events at YAK and YXY, which suggests that this cold and dry air source over the interior is an important ingredient for the development of sharp frontlike boundaries to the barrier jet. In contrast, the variable jets have weaker low-level stability, which favors the subsequent mixing of higher momentum to the surface in localized areas. The warm season jets also have cooler lower levels than those for the nonjet events, but the lower levels are nearly well mixed with little stratification, especially over the interior.

The Environment

Hindsight is usually expressed in bravado-tinged phrases. “You have it so easy now” is one. But when scanning the recent history of environmental news, the impression is just the opposite. A few decades ago, anyone with a notepad or camera could have looked almost anywhere and chronicled a vivid trail of despoliation and disregard. Only a few journalists and authors, to their credit, were able to recognize a looming disaster hiding in plain sight. But at least it was in plain sight. The challenges in covering environmental problems today are far greater, for a host of reasons. Some relate to the subtlety or complexity of most remaining pollution and ecological issues now that glaring problems have been attacked. Think of non-point-source pollution, such as runoff from countless farm fields or urban lawns, and then think of the ultimate point of the Exxon Valdez, spilling its heavy load of crude oil into the seas off the Alaskan coast. A little reflection is useful. Most journalists of my generation were raised in an age of imminent calamity. Cold War “duck and cover” exercises regularly sent us to the school basement. The prospect of silent springs hung in the wind. We grew up in a landscape where environmental problems were easy to identify and describe. Depending on where you stood along the Hudson River's banks, the shores were variously coated with adhesive, dyes, paint, or other materials indicating which riverfront factory was nearest. And, of course, the entire river was a repository for human waste, making most sections unswimmable. Smokestacks were unfiltered. Gasoline was leaded. Then things began to change. New words crept into the popular lexicon—smog, acid rain, toxic waste. At the same time, citizens gained a sense of empowerment as popular protest shortened a war. A new target was pollution. Earth Day was something newspapers wrote about with vigor, not an anachronistic, even quaint, notion. Republican administrations and bipartisan Congresses created a suite of laws aimed at restoring air and water quality and protecting wildlife. And, remarkably, those laws began to work. Right through the 19805 the prime environmental issues of the day—and thus the news—continued to revolve around iconic incidents, mainly catastrophic in nature.

Middle Pleistocene to Holocene palynostratigraphy of Ocean Drilling Program Site 887 in the Gulf of Alaska, northeastern North Pacific

A palynological investigation was undertaken on the upper 29 m of sediment at Ocean Drilling Program (ODP) Site 887, spanning the last 430 000 years (i.e., isotopic stages 12 to 1). Pollen and dinocyst assemblages reveal a major ecostratigraphical boundary at the Middle–Late Pleistocene transition. The Middle Pleistocene pollen data document the occurrence of a spruce forest vegetation in the source area, likely located on the adjacent Alaskan coast, whereas the Late Pleistocene is marked by higher inputs of pine, shrub, and herb taxa, suggesting predominant inputs from a more open landscape. The Middle Pleistocene is characterized by a low diversity in dinocyst assemblages, which are dominated by Operculodinium centrocarpum, whereas the Late Pleistocene is marked by the significant occurrence of Pentapharsodinium dalei, Pyxidinopsis reticulata, and by high percentages of Brigantedinium spp. Such assemblages suggest open oceanic and cool temperate conditions during the Middle Pleistocene, changing toward generally colder and less saline conditions during the Late Pleistocene. In addition, large fluctuations in the dinocyst assemblages during the Late Pleistocene are recorded in phase with the main shifts in the isotopic stratigraphy. A new dinocyst taxon, Spiniferites alaskensis sp. nov., exclusively recorded in sediments of the isotopic substage 5e, is described herein.

El Niño and its impact on fire weather conditions in Alaska

Examining the relationship of El Niño to weather patterns in Alaska shows wide climate variances that depend on the teleconnection between the tropics and the northern latitudes. However, the weather patterns exhibited in Alaska during and just after moderate to strong El Niño episodes are generally consistent: above normal temperature and precipitation along the Alaskan coast, and above normal temperature and below normal precipitation in the interior, especially through the winter. The warm, dry conditions in the Alaskan interior increase summer wildfire potential. Statistics on the area burned since 1940 show that 15 out of 17 of the biggest fire years occurred during a moderate to strong El Niño episode. These 15 years account for nearly 63% of the total area burned over the last 58 years. Evidence points to increased dry thunderstorms and associated lightning activity during an El Niño episode; the percentage of total area burned by lightning caused fires during five episodes increased from a normal of less than 40% to a high of about 96%.

Ice in the shore zone and the geomorphology of cold coasts

Approximately 90% of Canada's ocean coastline is affected by seasonal or multiyear sea ice and winter ice develops on most lakes. Recent studies of ice effects in the shore zone have included investigations of ice-congested and protected shores in the north-west Canadian Arctic Archipelago, processes involved in the construction by ice of large shore ridges in the same region, direct ice scour and enhanced hydrodynamic scour in the presence of ice (strudel scour and ice wallow), particularly as potential hazards to buried pipelines in the Beaufort Sea, and the dynamics of boulder-strewn tidal flats and boulder barricades in eastern Canada. The extent and frequency of shore nourishment by ice and details of the processes involved, including the relative importance of ride-up versus pile-up, remain important research questions. Reports emphasizing the contribution of ice rafting to shoreface retreat along the Alaskan coast of the Beaufort Sea suggest the need for quantitative studies of this phenomenon in Canada, in particular with respect to prodelta sedimentation at the mouth of the Mackenzie River. The coastal zone in the Beaufort Sea is particularly sensitive to climate change through effects on thermokarst processes, rising sea level, the relation between ice cover and wave energy through fetch limitation, and potential changes involving ice dynamics and freeze-up processes.