Aleutian Low

Abstract The seasonal change in the development of Aleutian low pressure systems from early fall to early winter is analyzed using a combination of meteorological reanalysis fields, satellite sea surface temperature (SST) data, and satellite wind data. The time period of the study is September–December 2002, although results are shown to be representative of the long-term climatology. Characteristics of the storms were documented as they progressed across the North Pacific, including their path, central pressure, deepening rate, and speed of translation. Clear patterns emerged. Storms tended to deepen in two distinct geographical locations—the Gulf of Alaska in early fall and the western North Pacific in late fall. In the Gulf of Alaska, a quasi-permanent “notch” in the SST distribution is argued to be of significance. The signature of the notch is imprinted in the atmosphere, resulting in a region of enhanced cyclonic potential vorticity in the lower troposphere that is conducive for storm development. Later in the season, as winter approaches and the Sea of Okhotsk becomes partially ice covered and cold, the air emanating from the Asian continent leads to enhanced baroclinicity in the region south of Kamchatka. This corresponds to enhanced storm cyclogenesis in that region. Consequently, there is a seasonal westward migration of the dominant lobe of the Aleutian low. The impact of the wind stress curl pattern resulting from these two regions of storm development on the oceanic circulation is investigated using historical hydrography. It is argued that the seasonal bimodal input of cyclonic vorticity from the wind may be partly responsible for the two distinct North Pacific subarctic gyres.

Download Full-text

Solar Cycle Signals in the Pacific and the Issue of Timings

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-0277.1 ◽

2012 ◽

Vol 69 (4) ◽

pp. 1446-1451 ◽

Cited By ~ 30

Author(s):

Indrani Roy ◽

Joanna D. Haigh

Keyword(s):

Solar Activity ◽

Solar Cycle ◽

Aleutian Low ◽

Positive Signal ◽

Tropical Eastern Pacific ◽

Sea Level Pressure ◽

The Pacific ◽

Strong Positive Signal ◽

The Relationship ◽

The Tropical Pacific

Abstract The solar cycle signal in sea level pressure during 1856–2007 is analyzed. Using composites of data from January–February in solar cycle peak years the strong positive signal in the region of the Aleutian low, found by previous authors, is confirmed. It is found, however, that signals in other regions of the globe, particularly in the South Pacific, are very sensitive to the choice of reference climatology. Also investigated is the relationship between solar activity and sea surface temperatures in the tropical eastern Pacific. A marked overall association of higher solar activity with colder temperatures in the tropical Pacific that is not restricted to years of peak sunspot number is noted. The ENSO-like variation following peak years that has been suggested by other authors is not found as a consistent signal. Both the SLP and SST signals vary coherently with the solar cycle and neither evolves on an ENSO-like time scale. The solar signals are weaker during the period spanning approximately 1956–97, which may be due to masking by a stronger innate ENSO variability at that time.

Download Full-text

A Synoptic Analysis of the Interannual Variability of Winter Cyclone Activity in the Aleutian Low Region

Journal of Climate ◽

10.1175/jcli4077.1 ◽

2007 ◽

Vol 20 (8) ◽

pp. 1523-1538 ◽

Cited By ~ 16

Author(s):

Xiaojie Zhu ◽

Jilin Sun ◽

Zhengyu Liu ◽

Qinyu Liu ◽

Jonathan E. Martin

Keyword(s):

North Pacific ◽

Aleutian Low ◽

Cyclone Activity ◽

Cyclone Intensity ◽

Low Intensity ◽

Interannual Change ◽

The North ◽

Relative Change ◽

Cyclone Frequency ◽

The North Pacific

Abstract An analysis of cyclone activity in winter associated with years of strong and weak Aleutian low in the North Pacific is presented. From 1958 to 2004, 10 winters with a strong Aleutian low are defined as the strong years, while 8 winters with a weak Aleutian low are defined as the weak years. Employing a system-centered Lagrangian method, some characteristics of the cyclone activity in both sets of years are revealed. The cyclone frequency, duration, and intensity are nearly the same in both strong and weak years. The cyclone tracks in the strong years are more zonal than those in the weak years. More intense cyclone events and more large cyclone cases occur in strong years than in weak years and the deepening of cyclones in strong years is stronger than that in weak years. The analyses of geopotential height, wind, stationary Rossby wavenumber, and Eady growth rate index at 500 or 300 hPa reveal that conditions are favorable for more zonal tracks and greater cyclone growth in strong years than in weak years. An estimation of the relative change of cyclone intensity and the relative change of Aleutian low intensity is made, which shows that the interannual change of cyclone intensity is about 73% of the interannual change of Aleutian low intensity. This result suggests that the evolution of individual cyclones may be a significant driver of changes in the Aleutian low.

Download Full-text

Climate and vegetation history from a 14,000-year peatland record, Kenai Peninsula, Alaska

Quaternary Research ◽

10.1016/j.yqres.2009.04.002 ◽

2009 ◽

Vol 72 (2) ◽

pp. 207-217 ◽

Cited By ~ 35

Author(s):

Miriam C. Jones ◽

Dorothy M. Peteet ◽

Dorothy Kurdyla ◽

Thomas Guilderson

Keyword(s):

Vegetation History ◽

Younger Dryas ◽

Aleutian Low ◽

High Moisture ◽

Wet Meadow ◽

Kenai Peninsula ◽

Tundra Vegetation ◽

Climatic Cooling ◽

Vegetation And Climate ◽

Meadow Species

AbstractAnalysis of pollen, spores, macrofossils, and lithology of an AMS 14C-dated core from a subarctic fen on the Kenai Peninsula, Alaska reveals changes in vegetation and climate beginning 14,200 cal yr BP. Betula expansion and contraction of herb tundra vegetation characterize the Younger Dryas on the Kenai, suggesting increased winter snowfall concurrent with cool, sunny summers. Remarkable Polypodiaceae (fern) abundance between 11,500 and 8500 cal yr BP implies a significant change in climate. Enhanced peat preservation and the occurrence of wet meadow species suggest high moisture from 11,500 to 10,700 cal yr BP, in contrast to drier conditions in southeastern Alaska; this pattern may indicate an intensification and repositioning of the Aleutian Low (AL). Drier conditions on the Kenai Peninsula from 10,700 to 8500 cal yr BP may signify a weaker AL, but elevated fern abundance may have been sustained by high seasonality with substantial snowfall and enhanced glacial melt. Decreased insolation-induced seasonality resulted in climatic cooling after 8500 cal yr BP, with increased humidity from 8000 to 5000 cal yr BP. A dry interval punctuated by volcanic activity occurred between 5000 and 3500 cal yr BP, followed by cool, moist climate, coincident with Neoglaciation. Tsuga mertensiana expanded after ~ 1500 cal yr BP in response to the shift to cooler conditions.

Download Full-text

RELATIONSHIP BETWEEN SUMMER TROPICAL CYCLONE GENESIS FREQUENCY AND WINTER ALEUTIAN LOW OSCILLATION

Advances in Geosciences - A 6-Volume Set - Volume 16: Atmospheric Science(AS) ◽

10.1142/9789812838100_0016 ◽

2010 ◽

pp. 179-191

Author(s):

KI-SEON CHOI ◽

DO-WOO KIM ◽

SU-BIN OH ◽

JI-SUN LEE ◽

HI-RYONG BYUN

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclone Genesis ◽

Aleutian Low ◽

Cyclone Genesis ◽

Genesis Frequency

Download Full-text

Recent Warming in the Western North Pacific in Relation to Rapid Changes in the Atmospheric Circulation of the Siberian High and Aleutian Low Systems*

Journal of Climate ◽

10.1175/2011jcli4142.1 ◽

2012 ◽

Vol 25 (10) ◽

pp. 3476-3493 ◽

Cited By ~ 27

Author(s):

Young-Hyang Park ◽

Jong-Hwan Yoon ◽

Yong-Hoon Youn ◽

Frédéric Vivier

Keyword(s):

Wind Stress ◽

North Pacific ◽

Western North Pacific ◽

Rossby Waves ◽

Delayed Response ◽

Aleutian Low ◽

Wind Stress Curl ◽

Siberian High ◽

Sst Variability ◽

The Kuroshio

Abstract On the basis of a new East Asian winter monsoon (EAWM) index and by analyzing the relationship between sea surface temperature (SST) anomalies and different atmospheric and oceanic factors in winter, this study investigates the causes of the recent unusual warming in the western North Pacific Ocean. Analyses presented here emphasize the dual contribution from the atmosphere and ocean to the local SST variability, with the relative importance of each contributor varying with the period and place. During the period 1970–89, the EAWM, controlled mostly by the Siberian high, is predominantly responsible for the SST variability in most of the western North Pacific, whereas in the period 1990–2005 ocean dynamics become increasingly important in most places or even dominant in the Kuroshio–Oyasio Extension (KOE) region. The delayed response of the KOE SST to basinwide wind stress curl forcing via Rossby waves is epoch dependent and is significant at lags of 1, 3, and 4 yr before 1990 but only at 1 yr afterward. This epoch dependency of the impact of Rossby waves is related to the different locations of the centers of action of wind stress curl in the midlatitude North Pacific between the two epochs. In addition, mean advection of the EAWM-driven anomalous SST from the southern East China Sea, which can be transported into the KOE region in about a year by the Kuroshio, likely affects the KOE SST lagged by 1 yr. The strongest positive SST trend observed in the western North Pacific results from the combined effects of the abrupt weakening of the EAWM due to the unprecedented decline of the Siberian high and the increasing role of the ocean. The latter is best evidenced by the 1-yr delayed response of the western North Pacific via the gyre circulation adjustment to the basinwide decadal-scale wind stress curl change associated with the northward shift of the strengthened Aleutian low.

Download Full-text

Evidence for a 55–50 ka (early Wisconsin) glaciation of the Cordilleran ice sheet, Yukon Territory, Canada

Quaternary Research ◽

10.1016/j.yqres.2007.04.002 ◽

2007 ◽

Vol 68 (1) ◽

pp. 141-150 ◽

Cited By ~ 33

Author(s):

Brent C. Ward ◽

Jeffrey D. Bond ◽

John C. Gosse

Keyword(s):

Ice Sheet ◽

Yukon Territory ◽

Canadian Cordillera ◽

Aleutian Low ◽

Climatic Forcing ◽

Apparent Contrast ◽

Oxygen Isotope Stage ◽

Source Areas ◽

Cordilleran Ice Sheet ◽

Exposure Ages

AbstractCosmogenic 10Be ages on boulders of 54–51 ka (n=4) on a penultimate Cordilleran ice sheet (CIS) drift confirm that Marine Oxygen Isotope Stage (MIS) 4 (early Wisconsin) glaciation was extensive in parts of Yukon Territory, the first confirmed evidence in the Canadian Cordillera. We name the glaciation inferred from the mapped and dated drift the Gladstone. These results are in apparent contrast to the MIS 6 (Illinoian) age of the penultimate Reid glaciation to the east in central Yukon but are equivalent to exposure ages on MIS 4 drift in Alaska. Contrasting penultimate ice extents in Yukon requires that different source areas of the northern CIS in Yukon responded differently to climatic forcing during glaciations. The variation in glacier extent for different source areas likely relates to variation in precipitation during glaciation, as the northern CIS was a precipitation-limited system. Causes for a variation in precipitation remain unclear but likely involve the style of precipitation delivery over the St. Elias Mountains possibly related to variations in the Aleutian low.

Download Full-text