One observed fingerprint of Pacific Arctic environmental change, induced by climate warming and a... more One observed fingerprint of Pacific Arctic environmental change, induced by climate warming and amplified local feedbacks, is a shift toward earlier onset of sea ice melt. Shorter freeze periods impact the melt season energy balance with cascading effects on ecological productivity and human presence in the region. Through this study, a non-linear technique, self-organizing maps, is utilized to investigate the subseasonal role of regional pressure patterns and associated lower-tropospheric wind regimes on melt onset in the Beaufort and Chukchi Seas. Focus is directed on the frequency and duration (≥ 3 consecutive days) of offshore, onshore, and zonal/weak flow that tend to precede anomalous (late and early) and average times of melt. Background North Pacific climate forcing ascribed from the Pacific Decadal Oscillation (PDO) phase and Bering Strait oceanic heat flux measurements provide a surface thermal context to the composite wind fields. In early melt onset years, onshore (northerly) winds occur approximately 1-3 fewer days with offsetting increases in zonal and offshore flow in the Beaufort and Chukchi Seas. During these cases, the Beaufort High pattern tends to setup more frequently around the southeastern Beaufort Sea region, yielding winds of a southerly and/or easterly nature that are enhanced by cyclone activity to the south or downstream. Chukchi Sea weather analyses, in particular, suggest that interacting, precursor mechanisms involving warm air advection off snow-free Arctic lands and from southerly latitudes coupled with a slightly positive PDO state and anomalous, poleward oceanic heat transfer condition the seasonal ice pack for increasingly early melt.
International Journal of Climatology, Jun 18, 2019
Winter weather in the subarctic and lower latitudes can be influenced by the repositioning of the... more Winter weather in the subarctic and lower latitudes can be influenced by the repositioning of the polar vortex away from being centered near the North Pole, extending over regional locations of subarctic continents. One example was the "Beast from the East" event in Eurasia in March 2018, which brought snow to much of Europe. We are interested in extended (week to a month) North American weather events, and especially the impacts from a location of the polar vortex center over and near Greenland. For a tropospheric polar vortex location index, we use low 500 hPa geopotential heights (GPH) over greater Greenland from values of the Greenland Blocking Index (GBI) below negative 1.0 standard deviation (1951-2018 base period). February is a preferred month with ten low GBI events beginning 1989. Composite 100 hPa and 500 hPa GPH for these ten cases show hemispheric-wide features with a trough/ridge/trough pattern extending from eastern Siberia eastward to Greenland and spanning both the stratospheric and tropospheric polar vortex. Associated extreme weather as seen in 2015 and 2018 include cold temperatures on the eastern United States, warm monthly temperatures (>5.0°C anomalies) in California with drought conditions, and record sea ice loss in the winter Bering Sea. Results support the concept that November-December has a regional tropospheric pathway for Arctic/midlatitude weather interactions due to delayed autumn sea ice freeze up, whereas January-March has a more hemispheric pathway related to stratospheric polar vortex movement that is delayed into late winter.
Pronounced changes in the Arctic environment add a new potential driver of anomalous weather patt... more Pronounced changes in the Arctic environment add a new potential driver of anomalous weather patterns in midlatitudes that affect billions of people. Recent studies of these Arctic/midlatitude weather linkages, however, state inconsistent conclusions. A source of uncertainty arises from the chaotic nature of the atmosphere. Thermodynamic forcing by a rapidly warming Arctic contributes to weather events through changing surface heat fluxes and large-scale temperature and pressure gradients. But internal shifts in atmospheric dynamics-the variability of the location, strength, and character of the jet stream, blocking, and stratospheric polar vortex (SPV)-obscure the direct causes and effects. It is important to understand these associated processes to differentiate Arctic-forced variability from natural variability. For example in early winter, reduced Barents/Kara Seas sea-ice coverage may reinforce existing atmospheric teleconnections between the North Atlantic/Arctic and central Asia, and affect downstream weather in East Asia. Reduced sea ice in the Chukchi Sea can amplify atmospheric ridging of high pressure near Alaska, influencing downstream weather across North America. In late winter southward displacement of the SPV, coupled to the troposphere, leads to weather extremes in Eurasia and North America. Combined tropical and sea ice conditions can modulate the variability of the SPV. Observational evidence for Arctic/midlatitude weather linkages continues to accumulate, along with understanding of connections with pre-existing climate states. Relative to natural atmospheric variability, sea-ice loss alone has played a secondary role in Arctic/midlatitude weather linkages; the full influence of Arctic amplification remains uncertain.
International Journal of Climatology, Oct 15, 2020
Siberia saw a heat wave of extreme monthly temperatures of +6° C anomalies from January through M... more Siberia saw a heat wave of extreme monthly temperatures of +6° C anomalies from January through May 2020, culminating with near daily temperature records at the Arctic station of Verhojansk in mid-June. This was a major Arctic event. The proximate cause for the warm extremes from January through April was the record strength of the stratospheric polar vortex (SPV) and tropospheric jet stream. The SPV and high geopotential heights to the south combined to provide strong zonal winds from the west that reduced the potential penetration of cold air from the north. An index of vortex strength is the Arctic Oscillation (AO); averaged over January-April, the AO set extreme positive records in 1989, 1990 and 2020 (baseline starting in 1950). The strength and stability of the SPV over the central Arctic contributed to the winterspring persistence of the heat wave in Siberia. May-June temperatures were related to high tropospheric geopotential heights over Asia. An open question is whether these dynamic events are becoming more persistent. Such record events will not occur every year but one can expect that they will occasionally naturally reoccur over the next decades due to internal atmospheric variability in addition to a continued global warming background.
Deep-sea Research Part Ii-topical Studies in Oceanography, Jun 1, 2018
With the sea-ice cover in the Arctic fast declining, changes to the timing of sea-ice break-up an... more With the sea-ice cover in the Arctic fast declining, changes to the timing of sea-ice break-up and freeze-up is an urgent economic, social, and scientific concern. Based on daily sea-ice concentration data we assess three variables: the dates of sea-ice break-up and freeze-up, and the annual sea-ice duration in the Pacific Arctic. The simulation results from the coupled Atmosphere-Ocean General Circulation Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are the source for this study. Compared with observations, CMIP5 models simulate all three variables well. The length of sea-ice duration is shrinking, with the strongest trend occurring for the period 1990-2014; this downward trend is projected to continue at least through mid-century by the CMIP5 models. Comparisons made at eight Chukchi Sea mooring sites and eight Distributed Biological Observatory (DBO) regions show consistent results. The 30-year averaged trend for annual sea-ice duration in the southern Chukchi Sea is projected to be −0.68 (−0.74) days/year to −1.20 (−1.17) days/year for 2015-2044 under RCP8.5 (RCP4.5) emissions scenarios. This is equivalent to a reduction of 20-36 days in the annual sea-ice duration. A similar negative trend is also found at all eight DBO regions. The reduction in annual sea-ice duration will include both earlier break-up dates and later freeze-up dates. However, models project that a later freeze-up contributes more than earlier break-up to the overall shortening of annual sea-ice duration. Around the Bering Strait area, future changes are the smallest, with less than 20 days change in duration during the next 30 years. In contrast, up to a 60-day reduction of the sea-ice duration in the East Siberian, Chukchi and Beaufort Seas is projected near the middle of the 21st century, when averaged over the period of 2030-2044.
Persistent near-surface warm temperature anomalies have occurred in two localized areas, eastern ... more Persistent near-surface warm temperature anomalies have occurred in two localized areas, eastern Siberia/East Siberian Sea and northeastern Canada/Baffin Bay, during winter and spring in recent years (2000-2005) in contrast to previous decades. The proximate cause in winter was a northward displacement and strengthening of the Aleutian Low and a weakening of the Icelandic Low. Spring showed a dipole pattern with higher sea-level pressure (SLP) on the North American side of the Arctic and lower pressures over Eurasia. Phase space trajectories of arctic climate for 1951-2005 based on the first two EOFs of SLP, the Arctic Oscillation and a Pacific North American-like (PNA*) pattern, show multi-annual variability leading to lower SLP and warmer temperatures in the last decades of the 20th century. Recent winters have some projection onto PNA*, but the SLP dipole in recent springs does not strongly project onto either of the two basic climate patterns. The period from 1928-1935 also had a dipole structure in SLP, which contributed to the interdecadal arctic-wide warm temperature anomalies in the first half of the 20th century. Recognition of the recent persistent and somewhat unique Arctic climate pattern is important as it contributes to the ongoing reorganization of arctic ecosystems.
The objective of this paper is to highlight those characteristics of climate variability that may... more The objective of this paper is to highlight those characteristics of climate variability that may pertain to the climate hypothesis regarding the long-term population decline of Steller sea lions (Eumetopias jubatus). The seasonal changes in surface air temperature (SAT) across the Aleutian Islands are relatively uniform, from 5 to 10°C in summer to near freezing temperatures in winter. The interannual and interdecadal variations in SAT, however, are substantially different for the eastern and western Aleutians, with the transition found at about 170°W. The eastern Aleutians experienced a regime shift toward a warmer climate in 1977, simultaneously with the basin-wide shift in the Pacific Decadal Oscillation (PDO). In contrast, the western Aleutians show a steady decline in winter SATs that started in the 1950s. This cooling trend was accompanied by a trend toward more variable SAT, both on the inter-and intra-annual time scale. During 1986-2002, the variance of winter SATs more than doubled compared to 1965-1985. At the same time in Southeast Alaska, the SAT variance diminished by half. Much of the increase in the intra-seasonal variability for the western Aleutians is associated with a warming trend in November and a cooling trend in January. As a result, the rate of seasonal cooling from November to January has doubled since the late 1950s. We hypothesize that this trend in SAT variability may have increased the environmental stress on the western stock of Steller sea lions and hence contributed to its decline.
The many recent publications on regimes and shifts highlight the importance of decadal variabilit... more The many recent publications on regimes and shifts highlight the importance of decadal variability in understanding climate and ecosystems and their connectivity. This paper explores several issues in the application of regime concepts. Even the definition of regimes is unclear, as usage by different authors highlight: (1) displacement or shifts in timeseries, (2) underlying mechanisms, and (3) the distinction between external forcing and internal reorganization of ecosystems. Such differences arise, and cannot be easily resolved, because of the relatively short duration of available physical and biological timeseries, and the complexity of multivariate process in marine systems with unknown variables and relationships. Climate indices often show a rather Gaussian distribution of values with a single mean, rather than clearly separated discrete multiple states. These physical indices can be represented by a red noise long memory process, where the index can, in fact, deviate substantially from the long term mean for multiple years. If we consider changes in timeseries themselves, then climate variables for the North Pacific display shifts near 1977, 1989 and 1998. Recent variability suggests considerable uncertainty in the current state of the North Pacific. Biological variables often show a broader distribution of shifts over time, which is consistent with different types of responses to climate for different ecosystem elements and the importance of time lags in response to changes in physical forcing. Our current understanding of regime shifts is not a deterministic one, and while one can discuss amplitudes and mean duration of regimes, we cannot predict their precise timing other than to say that they will be a main feature of future climate and ecosystem states. While the authors believe that a single definition for regimes is currently not possible, the concept continues to be useful in moving the discussion of ecosystems away from the assumptions of single species and stationary processes.
The January–February mean central pressure of the Aleutian low is investigated as an index of Nor... more The January–February mean central pressure of the Aleutian low is investigated as an index of North Pacific variability on interannual to decadal timescales. Since the turn of the century, 37% of the winter interannual variance of the Aleutian low is on timescales greater than 5 ...
Deep-sea Research Part Ii-topical Studies in Oceanography, Jun 1, 2012
The meteorology and oceanography of the southeastern Bering Sea shelf was recently dominated by a... more The meteorology and oceanography of the southeastern Bering Sea shelf was recently dominated by a multi-year warm event (2000-2005) followed by a multi-year cold event (2007-2010). We put these recent events into the context of the 95-year air temperature record from St. Paul Island and with concurrent spatial meteorological fields. For March 2000-2005 the mean air temperature anomaly at St. Paul was 2.1 1C above the long-term mean, and for March 2007-2010 the mean temperature anomaly at St. Paul was 4.7 1C below the long-term mean. The only multi-year temperature deviations comparable to the first decade of the 2000s are a cold event from 1971 to 1976 followed by a warm event from 1978 to 1983. There was also a short warm event 1935-1937. The temperature transition between warm and cold events in the 1970s and 2000s took two years. While there are theoretical arguments for some physical memory processes in the North Pacific climate system, we cannot rule out that the recent warm and cold events are of a random nature: they are rare in the St. Paul temperature record, they are dominated by North Pacific-wide sea level pressure events rather than local Bering Sea processes, and they are consistent with a red noise model of climate variability. The 1970s transition appears to have an ENSO (El Niñ o-Southern Oscillation) influence, while the recent events are likely connected to Arctic-wide warming. Evidence provided by the 95-year St. Paul meteorological record reinforces the idea that a red-noise model of climate variability is appropriate for the North Pacific and southeastern Bering Sea. We stress the importance of relatively rare sub-decadal events and shifts, rather than multi-decadal variability associated with the Pacific Decadal Oscillation (PDO). Thus, in the future we can expect large positive and negative excursions in the region that can last for multiple years, but there is as yet little predictability for their timing and duration.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
One observed fingerprint of Pacific Arctic environmental change, induced by climate warming and a... more One observed fingerprint of Pacific Arctic environmental change, induced by climate warming and amplified local feedbacks, is a shift toward earlier onset of sea ice melt. Shorter freeze periods impact the melt season energy balance with cascading effects on ecological productivity and human presence in the region. Through this study, a non-linear technique, self-organizing maps, is utilized to investigate the subseasonal role of regional pressure patterns and associated lower-tropospheric wind regimes on melt onset in the Beaufort and Chukchi Seas. Focus is directed on the frequency and duration (≥ 3 consecutive days) of offshore, onshore, and zonal/weak flow that tend to precede anomalous (late and early) and average times of melt. Background North Pacific climate forcing ascribed from the Pacific Decadal Oscillation (PDO) phase and Bering Strait oceanic heat flux measurements provide a surface thermal context to the composite wind fields. In early melt onset years, onshore (northerly) winds occur approximately 1-3 fewer days with offsetting increases in zonal and offshore flow in the Beaufort and Chukchi Seas. During these cases, the Beaufort High pattern tends to setup more frequently around the southeastern Beaufort Sea region, yielding winds of a southerly and/or easterly nature that are enhanced by cyclone activity to the south or downstream. Chukchi Sea weather analyses, in particular, suggest that interacting, precursor mechanisms involving warm air advection off snow-free Arctic lands and from southerly latitudes coupled with a slightly positive PDO state and anomalous, poleward oceanic heat transfer condition the seasonal ice pack for increasingly early melt.
International Journal of Climatology, Jun 18, 2019
Winter weather in the subarctic and lower latitudes can be influenced by the repositioning of the... more Winter weather in the subarctic and lower latitudes can be influenced by the repositioning of the polar vortex away from being centered near the North Pole, extending over regional locations of subarctic continents. One example was the "Beast from the East" event in Eurasia in March 2018, which brought snow to much of Europe. We are interested in extended (week to a month) North American weather events, and especially the impacts from a location of the polar vortex center over and near Greenland. For a tropospheric polar vortex location index, we use low 500 hPa geopotential heights (GPH) over greater Greenland from values of the Greenland Blocking Index (GBI) below negative 1.0 standard deviation (1951-2018 base period). February is a preferred month with ten low GBI events beginning 1989. Composite 100 hPa and 500 hPa GPH for these ten cases show hemispheric-wide features with a trough/ridge/trough pattern extending from eastern Siberia eastward to Greenland and spanning both the stratospheric and tropospheric polar vortex. Associated extreme weather as seen in 2015 and 2018 include cold temperatures on the eastern United States, warm monthly temperatures (>5.0°C anomalies) in California with drought conditions, and record sea ice loss in the winter Bering Sea. Results support the concept that November-December has a regional tropospheric pathway for Arctic/midlatitude weather interactions due to delayed autumn sea ice freeze up, whereas January-March has a more hemispheric pathway related to stratospheric polar vortex movement that is delayed into late winter.
Pronounced changes in the Arctic environment add a new potential driver of anomalous weather patt... more Pronounced changes in the Arctic environment add a new potential driver of anomalous weather patterns in midlatitudes that affect billions of people. Recent studies of these Arctic/midlatitude weather linkages, however, state inconsistent conclusions. A source of uncertainty arises from the chaotic nature of the atmosphere. Thermodynamic forcing by a rapidly warming Arctic contributes to weather events through changing surface heat fluxes and large-scale temperature and pressure gradients. But internal shifts in atmospheric dynamics-the variability of the location, strength, and character of the jet stream, blocking, and stratospheric polar vortex (SPV)-obscure the direct causes and effects. It is important to understand these associated processes to differentiate Arctic-forced variability from natural variability. For example in early winter, reduced Barents/Kara Seas sea-ice coverage may reinforce existing atmospheric teleconnections between the North Atlantic/Arctic and central Asia, and affect downstream weather in East Asia. Reduced sea ice in the Chukchi Sea can amplify atmospheric ridging of high pressure near Alaska, influencing downstream weather across North America. In late winter southward displacement of the SPV, coupled to the troposphere, leads to weather extremes in Eurasia and North America. Combined tropical and sea ice conditions can modulate the variability of the SPV. Observational evidence for Arctic/midlatitude weather linkages continues to accumulate, along with understanding of connections with pre-existing climate states. Relative to natural atmospheric variability, sea-ice loss alone has played a secondary role in Arctic/midlatitude weather linkages; the full influence of Arctic amplification remains uncertain.
International Journal of Climatology, Oct 15, 2020
Siberia saw a heat wave of extreme monthly temperatures of +6° C anomalies from January through M... more Siberia saw a heat wave of extreme monthly temperatures of +6° C anomalies from January through May 2020, culminating with near daily temperature records at the Arctic station of Verhojansk in mid-June. This was a major Arctic event. The proximate cause for the warm extremes from January through April was the record strength of the stratospheric polar vortex (SPV) and tropospheric jet stream. The SPV and high geopotential heights to the south combined to provide strong zonal winds from the west that reduced the potential penetration of cold air from the north. An index of vortex strength is the Arctic Oscillation (AO); averaged over January-April, the AO set extreme positive records in 1989, 1990 and 2020 (baseline starting in 1950). The strength and stability of the SPV over the central Arctic contributed to the winterspring persistence of the heat wave in Siberia. May-June temperatures were related to high tropospheric geopotential heights over Asia. An open question is whether these dynamic events are becoming more persistent. Such record events will not occur every year but one can expect that they will occasionally naturally reoccur over the next decades due to internal atmospheric variability in addition to a continued global warming background.
Deep-sea Research Part Ii-topical Studies in Oceanography, Jun 1, 2018
With the sea-ice cover in the Arctic fast declining, changes to the timing of sea-ice break-up an... more With the sea-ice cover in the Arctic fast declining, changes to the timing of sea-ice break-up and freeze-up is an urgent economic, social, and scientific concern. Based on daily sea-ice concentration data we assess three variables: the dates of sea-ice break-up and freeze-up, and the annual sea-ice duration in the Pacific Arctic. The simulation results from the coupled Atmosphere-Ocean General Circulation Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are the source for this study. Compared with observations, CMIP5 models simulate all three variables well. The length of sea-ice duration is shrinking, with the strongest trend occurring for the period 1990-2014; this downward trend is projected to continue at least through mid-century by the CMIP5 models. Comparisons made at eight Chukchi Sea mooring sites and eight Distributed Biological Observatory (DBO) regions show consistent results. The 30-year averaged trend for annual sea-ice duration in the southern Chukchi Sea is projected to be −0.68 (−0.74) days/year to −1.20 (−1.17) days/year for 2015-2044 under RCP8.5 (RCP4.5) emissions scenarios. This is equivalent to a reduction of 20-36 days in the annual sea-ice duration. A similar negative trend is also found at all eight DBO regions. The reduction in annual sea-ice duration will include both earlier break-up dates and later freeze-up dates. However, models project that a later freeze-up contributes more than earlier break-up to the overall shortening of annual sea-ice duration. Around the Bering Strait area, future changes are the smallest, with less than 20 days change in duration during the next 30 years. In contrast, up to a 60-day reduction of the sea-ice duration in the East Siberian, Chukchi and Beaufort Seas is projected near the middle of the 21st century, when averaged over the period of 2030-2044.
Persistent near-surface warm temperature anomalies have occurred in two localized areas, eastern ... more Persistent near-surface warm temperature anomalies have occurred in two localized areas, eastern Siberia/East Siberian Sea and northeastern Canada/Baffin Bay, during winter and spring in recent years (2000-2005) in contrast to previous decades. The proximate cause in winter was a northward displacement and strengthening of the Aleutian Low and a weakening of the Icelandic Low. Spring showed a dipole pattern with higher sea-level pressure (SLP) on the North American side of the Arctic and lower pressures over Eurasia. Phase space trajectories of arctic climate for 1951-2005 based on the first two EOFs of SLP, the Arctic Oscillation and a Pacific North American-like (PNA*) pattern, show multi-annual variability leading to lower SLP and warmer temperatures in the last decades of the 20th century. Recent winters have some projection onto PNA*, but the SLP dipole in recent springs does not strongly project onto either of the two basic climate patterns. The period from 1928-1935 also had a dipole structure in SLP, which contributed to the interdecadal arctic-wide warm temperature anomalies in the first half of the 20th century. Recognition of the recent persistent and somewhat unique Arctic climate pattern is important as it contributes to the ongoing reorganization of arctic ecosystems.
The objective of this paper is to highlight those characteristics of climate variability that may... more The objective of this paper is to highlight those characteristics of climate variability that may pertain to the climate hypothesis regarding the long-term population decline of Steller sea lions (Eumetopias jubatus). The seasonal changes in surface air temperature (SAT) across the Aleutian Islands are relatively uniform, from 5 to 10°C in summer to near freezing temperatures in winter. The interannual and interdecadal variations in SAT, however, are substantially different for the eastern and western Aleutians, with the transition found at about 170°W. The eastern Aleutians experienced a regime shift toward a warmer climate in 1977, simultaneously with the basin-wide shift in the Pacific Decadal Oscillation (PDO). In contrast, the western Aleutians show a steady decline in winter SATs that started in the 1950s. This cooling trend was accompanied by a trend toward more variable SAT, both on the inter-and intra-annual time scale. During 1986-2002, the variance of winter SATs more than doubled compared to 1965-1985. At the same time in Southeast Alaska, the SAT variance diminished by half. Much of the increase in the intra-seasonal variability for the western Aleutians is associated with a warming trend in November and a cooling trend in January. As a result, the rate of seasonal cooling from November to January has doubled since the late 1950s. We hypothesize that this trend in SAT variability may have increased the environmental stress on the western stock of Steller sea lions and hence contributed to its decline.
The many recent publications on regimes and shifts highlight the importance of decadal variabilit... more The many recent publications on regimes and shifts highlight the importance of decadal variability in understanding climate and ecosystems and their connectivity. This paper explores several issues in the application of regime concepts. Even the definition of regimes is unclear, as usage by different authors highlight: (1) displacement or shifts in timeseries, (2) underlying mechanisms, and (3) the distinction between external forcing and internal reorganization of ecosystems. Such differences arise, and cannot be easily resolved, because of the relatively short duration of available physical and biological timeseries, and the complexity of multivariate process in marine systems with unknown variables and relationships. Climate indices often show a rather Gaussian distribution of values with a single mean, rather than clearly separated discrete multiple states. These physical indices can be represented by a red noise long memory process, where the index can, in fact, deviate substantially from the long term mean for multiple years. If we consider changes in timeseries themselves, then climate variables for the North Pacific display shifts near 1977, 1989 and 1998. Recent variability suggests considerable uncertainty in the current state of the North Pacific. Biological variables often show a broader distribution of shifts over time, which is consistent with different types of responses to climate for different ecosystem elements and the importance of time lags in response to changes in physical forcing. Our current understanding of regime shifts is not a deterministic one, and while one can discuss amplitudes and mean duration of regimes, we cannot predict their precise timing other than to say that they will be a main feature of future climate and ecosystem states. While the authors believe that a single definition for regimes is currently not possible, the concept continues to be useful in moving the discussion of ecosystems away from the assumptions of single species and stationary processes.
The January–February mean central pressure of the Aleutian low is investigated as an index of Nor... more The January–February mean central pressure of the Aleutian low is investigated as an index of North Pacific variability on interannual to decadal timescales. Since the turn of the century, 37% of the winter interannual variance of the Aleutian low is on timescales greater than 5 ...
Deep-sea Research Part Ii-topical Studies in Oceanography, Jun 1, 2012
The meteorology and oceanography of the southeastern Bering Sea shelf was recently dominated by a... more The meteorology and oceanography of the southeastern Bering Sea shelf was recently dominated by a multi-year warm event (2000-2005) followed by a multi-year cold event (2007-2010). We put these recent events into the context of the 95-year air temperature record from St. Paul Island and with concurrent spatial meteorological fields. For March 2000-2005 the mean air temperature anomaly at St. Paul was 2.1 1C above the long-term mean, and for March 2007-2010 the mean temperature anomaly at St. Paul was 4.7 1C below the long-term mean. The only multi-year temperature deviations comparable to the first decade of the 2000s are a cold event from 1971 to 1976 followed by a warm event from 1978 to 1983. There was also a short warm event 1935-1937. The temperature transition between warm and cold events in the 1970s and 2000s took two years. While there are theoretical arguments for some physical memory processes in the North Pacific climate system, we cannot rule out that the recent warm and cold events are of a random nature: they are rare in the St. Paul temperature record, they are dominated by North Pacific-wide sea level pressure events rather than local Bering Sea processes, and they are consistent with a red noise model of climate variability. The 1970s transition appears to have an ENSO (El Niñ o-Southern Oscillation) influence, while the recent events are likely connected to Arctic-wide warming. Evidence provided by the 95-year St. Paul meteorological record reinforces the idea that a red-noise model of climate variability is appropriate for the North Pacific and southeastern Bering Sea. We stress the importance of relatively rare sub-decadal events and shifts, rather than multi-decadal variability associated with the Pacific Decadal Oscillation (PDO). Thus, in the future we can expect large positive and negative excursions in the region that can last for multiple years, but there is as yet little predictability for their timing and duration.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Uploads
Papers by James Overland