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We characterize the differences in the upward planetary‐scale wave propagation during observed weak polar vortex (WPV) events between heavy‐ and light‐sea‐ice years in the Barents‐Kara Sea based on a composite analysis for the period of 1979–2015. Upward wave propagation during WPV events in heavy‐ice years is dominated by the wavenumber 1 component. In contrast, WPV events occurring in light‐ice years are characterized by stronger wavenumber 2 propagation, which is caused by the tropospheric wavenumber 2 response to sea‐ice reduction in the Barents‐Kara Sea. The above observed features are supported by an Atmospheric General Circulation Model experiment. Thus, under present climate conditions, Arctic sea‐ice loss is a possible factor modulating the wave propagation during the WPV events. We also find that the WPV events in light‐ice years have stronger stratosphere‐troposphere coupling, followed by colder midlatitude surface conditions particularly over Eurasia.

We propose a new scheme based on geopotential height fields to detect cutoff lows starting in the preexisting trough stage. The intensity and scale derived from the proposed scheme will allow for a better understanding of the cutoff low life cycle. These cutoff lows often accompany mesoscale disturbances, causing adverse weather-related events, such as intense torrential rainfall and/or tornadoes. The proposed scheme quantifies the geometric features of a depression from its horizontal height profile. The height slope of a line intersecting the depression bottom and the nearest tangential point (optimal slope) locally indicates the intensity and scale of an isolated depression.The strength of the proposed scheme is that, by removing a local background height slope from a geopotential height field, the cutoff low and its preexisting trough are seamlessly detected as an identical depression. The distribution maps for the detected cutoff lows and preexisting troughs are illustrated along with their intensities, sizes, and local background flows estimated from snapshot height fields. We conducted climatological comparisons of cutoff lows to determine the utility of the proposed scheme.

Cutoff lows are cyclones existing in the upper troposphere developing from precursory preexisting troughs. We introduce a new method to seamlessly detect cutoff lows and even preexisting troughs aiming to improve lead time of meso scale disturbances like tornadoes. The method is based on a geometric character; in this method, a slope defined as the tangential line from a minimum point of each height depression is measured on an isobaric surface. This slope evaluates an intensity and horizontal extension (radius) of each depression. Adopting a mathematical assumption, we successfully achieved to make an algorithm to separate the depression and the local background flow. To remove the background flow enables us to detect both cutoff lows and preexisting troughs seamlessly in reanalysis height fields. So, our method would allow the life cycle to be illustrated continuously from the birth of the cutoff low, that is, from the precursory preexisting trough, and is expected to contribute to the improvement of the lead time for predicting severe weathers. Some further application examples, including tornado accompanying cases, and even for blocking highs, would be shown.

The acoustic properties of a ground surface are well known to be affected strongly by soil moisture contents. Many studies have been conducted to quantify the effects through in-situ and laboratory measurements. The soil moisture is also well known to be influenced by continuous variability of meteorological elements such as rainfall, sunshine, and air temperature. Therefore, it is expected that the meteorological variability alters ground acoustic properties over time. For this study, an in-situ measurement campaign was held during July 2014 to January 2015 at a site in Niigata, Japan. An automatic weather station observed meteorological elements at 1-minute intervals. A buried soil moisture sensor measured water saturation in the ground near the station at 5-minute intervals. The acoustic absorption coefficient of the same ground position was measured once a day using an in-situ measurement technique. The observations showed that the absorption coefficient of the ground surface had variations with multiple timescales from days to months and seasons. Two-stage models of the influence of the weather on the absorption coefficient of the ground surface were derived from the data. The first stage models the short- and long-term effects of rainfall and the air temperature on the water saturation of the soil. The second stage models the effects of water saturation on the absorption coefficient of the ground. The derived models were found to explain the long-term and approximately half of the short-term variation of the acoustic absorption.

Recent evidence from both observations and model simulations suggests that an Arctic sea ice reduction tends to cause a negative Arctic Oscillation (AO) phase with severe winter weather in the Northern Hemisphere, which is often preceded by weakening of the stratospheric polar vortex. Although this evidence hints at a stratospheric involvement in the Arctic-midlatitude climate linkage, the exact role of the stratosphere remains elusive. Here we show that tropospheric AO response to the Arctic sea ice reduction largely disappears when suppressing the stratospheric wave mean flow interactions in numerical experiments. The results confirm a crucial role of the stratosphere in the sea ice impacts on the midlatitudes by coupling between the stratospheric polar vortex and planetary-scale waves. Those results and consistency with observation-based evidence suggest that a recent Arctic sea ice loss is linked to midlatitudes extreme weather events associated with the negative AO phase.

We investigated seasonal changes in carbon demand and flux by mesozooplankton communities at subtropical (S1) and subarctic sites (K2) in the western North Pacific Ocean to compare the impact of mesozooplankton communities on the carbon budget in surface and mesopelagic layers. Fecal pellet fluxes were one order higher at K2 than at S1, and seemed to be enhanced by copepod and euphausiid egestion under high chlorophyll a concentrations. The decrease in pellet volume and the lack of any substantial change in shape composition during sink suggest a decline in fecal pellet flux due to coprorhexy and coprophagy. While respiratory and excretory carbon by diel migrants at depth (i.e., active carbon flux) was similar between the two sites, the actively transported carbon exceeded sinking fecal pellets at S1. Mesozooplankton carbon demand in surface and mesopelagic layers was higher at K2 than S1, and an excess of demand to primary production and sinking POC flux was found during some seasons at K2. We propose that this demand was met by supplementary carbon sources such as feeding on protozoans and fecal pellets at the surface and carnivory of migrants at mesopelagic depths.

Rising atmospheric CO2 contents have led to greater CO2 uptake by the oceans, lowering both pH due to increasing hydrogen ions and CaCO3 saturation states due to declining carbonate ion (CO32−). Here we used previously compiled data sets and new data collected in 2010 and 2011 to investigate ocean acidification of the North Pacific western subarctic gyre. In winter, the western subarctic gyre is a source of CO2 to the atmosphere because of convective mixing of deep waters rich in dissolved inorganic carbon (DIC). We calculated pH in winter mixed layer from DIC and total alkalinity (TA), and found that it decreased at the rate of −0.0011 ± 0.0004 yr−1 from 1997 to 2011. This decrease rate is slower than that expected under the condition of seawater/atmosphere equilibration, and it is also slower than the rate in the subtropical regions (−0.002 yr−1). The slow rate is caused by a reduction of CO2 emission in winter due to an increase in TA. Below the mixed layer, the calcite saturation horizon (~ 185 m depth) shoaled at the rate of 2.9 ± 0.9 m yr−1 as the result of the declining CO32− concentration (−0.03 ± 0.01 μmol kg−1 yr−1). Between 200 m and 300 m depth, pH decline during the study period (−0.0051 ± 0.0010 yr−1) was larger than ever reported in the open North Pacific. This enhanced acidification rate below the calcite saturation horizon reflected not only the uptake of anthropogenic CO2 but also the increase in the decomposition of organic matter evaluated from the increase in AOU, which suggests that the dissolution of CaCO3 particles increased.

We studied time-series fluxes of diatom particles from 4 October 2010 to 18 September 2012 using bottom-tethered moorings with two sediment traps deployed at 180 and 1300 m depths at Station NAP (75° N, 162° W; 1975 m water depth) in the western Arctic Ocean. This paper discusses on the relationship of time-series diatom fluxes to satellite-based sea-ice motion and simulated hydrographic variations. We observed clear maxima of the diatom valve flux in November–December of both 2010 and 2011, and in August 2011. Diatoms in samples were categorized into 98 taxa. The diatom flux maxima were characterized by many resting spores in November–December and by the sea-ice-associated diatom Fossula arctica in August 2011. These assemblages along with abundant clay minerals in the samples suggest a significant influence of shelf-origin materials transported by mesoscale eddies, which developed along the Chukchi Sea shelf break. In contrast, the fluxes of total mass and diatoms were reduced in summer 2012. We hypothesize that this suppression reflects the influx of oligotrophic water originating from the central Canada Basin. A physical oceanographic model demonstrated that oligotrophic surface water from the Beaufort Gyre was supplied to Station NAP from December 2011 to the early half of 2012.

This paper examines the possible linkage between the recent reduction in Arctic sea-ice extent and the wintertime Arctic Oscillation (AO)/North Atlantic Oscillation (NAO). Observational analyses using the ERA interim reanalysis and merged Hadley/Optimum Interpolation Sea Surface Temperature data reveal that a reduced (increased) sea-ice area in November leads to more negative (positive) phases of the AO and NAO in early and late winter, respectively. We simulate the atmospheric response to observed sea-ice anomalies using a high-top atmospheric general circulation model (AGCM for Earth Simulator, AFES version 4.1). The results from the simulation reveal that the recent Arctic sea-ice reduction results in cold winters in mid-latitude continental regions, which are linked to an anomalous circulation pattern similar to the negative phase of AO/NAO with an increased frequency of large negative AO events by a factor of over two. Associated with this negative AO/NAO phase, cold air advection from the Arctic to the mid-latitudes increases. We found that the stationary Rossby wave response to the sea-ice reduction in the Barents Sea region induces this anomalous circulation. We also found a positive feedback mechanism resulting from the anomalous meridional circulation that cools the mid-latitudes and warms the Arctic, which adds an extra heating to the Arctic air column equivalent to about 60% of the direct surface heat release from the sea-ice reduction. The results from this high-top model experiment also suggested a critical role of the stratosphere in deepening the tropospheric annular mode and modulation of the NAO in mid to late winter through stratosphere-troposphere coupling.

We compared wintertime depth distributions of the mesozooplankton community and dominant copepods between the subtropical (S1) and subarctic (K2) Pacific Oceans to evaluate the relative importance of actively transported carbon by vertical migrants to sinking particulate organic carbon flux. Primary production was higher and the ratio of sinking particulate organic carbon flux to primary production was lower at S1 compared with those at K2. The mesozooplankton community was lower in abundance and biomass at S1 compared to K2. Copepods were the dominant group among both mesozooplankton abundance and biomass throughout the water column down to 1000 m at both sites. The depth distribution showed that diel vertical migration was obvious for the mesozooplankton abundance and biomass at S1 but was not apparent for the abundance at K2, because the dominant component was diurnally migrating species at S1 and overwintering species residing at mesopelagic depths at K2. The major components of diel migrants were copepods and euphausiids at S1 and only euphausiids at K2. Respiratory flux by the diurnally migrating mesozooplankton was estimated to be 2 mgC m −2 day −1 at S1 and 7 mgC m −2 day −1 at K2. The respiratory flux was equivalent to 131% of sedimentary fecal pellet flux at S1 and 136% of that at K2. Because pathways of downward carbon flux are facilitated by the mesozooplankton community, the actively transported carbon (respiration of dissolved inorganic carbon, excretion of dissolved organic carbon and egestion of fecal pellets at depth) might be larger during winter than the flux of sinking fecal pellets.

We demonstrated atmospheric responses to a reduction in Arctic sea ice via simulations in which Arctic sea ice decreased stepwise from the present-day range to an ice-free range. In all cases, the tropospheric response exhibited a negative Arctic Oscillation (AO)-like pattern. An intensification of the climatological planetary-scale wave due to the present-day sea ice reduction on the Atlantic side of the Arctic Ocean induced stratospheric polar vortex weakening and the subsequent negative AO. Conversely, strong Arctic warming due to ice-free conditions across the entire Arctic Ocean induced a weakening of the tropospheric westerlies corresponding to a negative AO without troposphere-stratosphere coupling, for which the planetary-scale wave response to a surface heat source extending to the Pacific side of the Arctic Ocean was responsible. Because the resultant negative AO-like response was accompanied by secondary circulation in the meridional plane, atmospheric heat transport into the Arctic increased, accelerating the Arctic amplification.

In the winter of 2009/2010, Japan and the East Asian region experienced a frequent occurrence of cold air outbreaks. Although the winter average temperature in the Japan main islands was slightly positive (+0.81°C for DJF average and +0.71°C for NDJFM average), repeated decline in temperature was notable throughout the season. One explanation for this abnormal winter season is the extremely negative condition of the Arctic Oscillation (AO) that persisted from December to mid-January. However, AO alone does not provide sufficient explanation for the cold air outbreak during November or its intraseasonal periodicity. A case study of the cold air outbreak that reached Japan on Dec. 18 reveals an anomalous ridge forming over the Barents-Kara Sea, which leads to the cold air accumulation over western Siberia. The pressure anomaly subsequently shifted westward to mature into a blocking high which created a wave-train pattern downstream, advecting the cold air eastward towards East Asia and Japan. The sequence of events was also apparent in multiple cases throughout the season. This study suggests that there is a strong and systematic linkage in the intraseasonal timescale between the atmospheric condition over the Barents-Kara Sea and the cold air accumulation over the Eurasian continent, leading to the anomalous cold air outbreak over East Asia and Japan. The mechanism may also provide explanation to extreme winter conditions such as those observed during the winter of 2010/2011.

Using an ensemble of wintertime hindcasts with a high-resolution (T106L60) Atmospheric General Circulation Model (AGCM) forced by observed sea surface temperatures (SSTs) and extending into the stratosphere, we investigate the formation and lifecycle of the Aleutian-Icelandic low Seesaw (AIS) during the 1978 to 1993 period. The AIS has been newly proposed to be an important mode of variability, linking the major wintertime surface lows, the Icelandic Low and the Aleutian Low, in late winter, and thereby linking climate variability over the North Pacific and the North Atlantic. We demonstrate for the first time with a stratosphere-troposphere model, that a coherent, ensemble-mean AIS extension into the stratosphere exists, where its presence modulates ultra-long planetary wave propagation and the polar night jet intensity. The model AIS peaks in February, when the Aleutian and Icelandic Low anti-correlation maximizes at -0.59. The AIS provides a new way to describe the El Nino-Southern Oscillation (ENSO) phenomenon influence into the stratosphere. For example, El-Nino conditions correspond to a deeper than normal Aleutian Low, extending its influence into the Icelandic sector as an AIS negative phase (weakened Icelandic Low), hence enhanced planetary wave vertical propagation and a weakened stratospheric polar vortex. This maturation of the AIS in late winter explains the intra-seasonal variability of the stratospheric response to ENSO, which peaks in late winter. Internal model variability is large and enhanced potential predictability is found primarily in the western hemisphere, with a western Atlantic maxima being more pronounced in the stratosphere than in the upper troposphere.

Inter-basin links between the North Pacific and North Atlantic in the wintertime upper-tropospheric circulation over the extratropical Northern Hemisphere, including their structure, dominance and seasonal dependence, are examined based on the structures of the leading EOFs for monthly height anomalies for the second half of the last century. Dominant variability in the upper troposphere is found to reflect the corresponding modulations in the strength of the inter-basin dynamical link between the North Pacific and North Atlantic. The first and second EOFs for the upper troposphere represent hemispheric patterns, showing the coherent variability between the North Pacific and North Atlantic. They essentially reflect the respective out-of-phase and in-phase relationships between the Icelandic low (IL) and Aleutian low (AL), as upper-level manifestations of the AL-IL seesaw and the cold ocean-warm land (COWL) pattern, respectively. Dominance of the AL-IL seesaw in the upper-tropospheric leading EOF is a manifestation of a dynamical linkage between the North Atlantic Oscillation and Pacific-North

The results of the empirical orthogonal function (EOF) analysis applied to the sea-level pressure (SLP) variability in the extratropical Northern Hemisphere is reexamined from viewpoint of statistical independence. For this purpose, “Independent Component Analysis” is introduced, whose effectiveness is demonstrated in its application to a set of simple hypothetical models. While its application to stratospheric variability confirms the relevance of the EOF analysis, its application to the SLP suggests that the two leading components of the EOF analysis are likely superpositions of two statistically independent signals. One of them represents a seesaw-like relationship in the intensities between the surface Aleutian and Icelandic lows, and the other is characterized by a significant long-term trend with the cold ocean-warm land pattern.

An interannual seesaw between the intensities of the Icelandic and Aleutian lows and its impact on surface climate observed during the twentieth century are investigated. In a recent period from the late 1960s to the early 1990s, their seesaw relationship was particularly apparent in late winter. The associated anomalies in surface air temperature were significant in many regions over the extratropical Northern Hemisphere except in central portions of the continents. The seesaw also modified the ocean–atmosphere exchange of heat and moisture extensively over the North Atlantic and North Pacific by changing evaporation and precipitation. Since the seesaw formation was triggered by eastward propagation of stationary Rossby wave trains from the North Pacific into the North Atlantic, anomalous circulation over the North Pacific in January was identified as a good precursor for February surface air temperatures in the Euro–Atlantic sector during that period. The seesaw relationship between the two lows underwent multidecadal modulations during the twentieth century. It was weak in the mid-1950s through the mid-1960s, while it was particularly strong during the preceding period from the 1920s to the 1940s with its impact on surface temperatures as extensive as in the recent period. Although it reached maturity in January, the precursory signal of the seesaw in that early period was also found in the North Pacific one month earlier, which suggests that the formation was through essentially the same mechanisms as in the recent period.

The potential predictability associated with the remote influence of midlatitude tropospheric anomalies over the North Pacific or the North Atlantic, via a seesawlike interannual oscillation between the surface Aleutian and Icelandic lows (AL and IL, respectively) is investigated. Data from a 24-member ensemble of 50-yr atmospheric general circulation model simulation forced with observed sea surface temperature (SST) conditions are analyzed by separating the total simulated fluctuations into the external component forced by the prescribed SST and the internal component generated by atmospheric internal dynamics. The AL–IL seesaw can be identified in both the external and internal components of the variability. In the external variability, determined through the ensemble mean, the seesaw is gradually formed from December to March through the development of a Pacific–North American (PNA) pattern–like wave train, remotely forced by the El Niño–Southern Oscillation. The amplitudes of the externally forced North Atlantic anomalies are only about half as large as the North Pacific anomalies. The potential predictability of the Atlantic anomalies, defined as the ratio of the SST-forced variance to the total variance, does not exceed the 20% level. In the internal component of the variability, determined from the deviations of each ensemble member from the ensemble mean, the negative correlation between the AL and IL anomalies is modest but persistent through winter. It is confirmed that, regardless of the polarity of the AL–IL seesaw, the IL anomalies are formed through eastward wave activity propagation of the stationary Rossby wave train emanating from the AL region in the form of what may be called a “PNAA pattern,” the extension of the PNA-like wave train into the Atlantic. Thus, the midwinter development of North Pacific anomalies is found to be a necessary, though not sufficient, condition for the seesaw formation. The persistence of the North Pacific anomalies beyond a 1-month time span appears to augment the probability of the seesaw formation by sustaining eastward wave activity propagation to the North Atlantic.

Heat transfer coefficients, and relative importance of factors affecting surface turbulent heat flux in sea-ice covered ocean, were investigated using data obtained by rawinsonde observations over, and around, the southwestern region of the Sea of Okhotsk from Jan. to Feb. in 1998, 1999 and 2000. The range of the fluxes estimated by an atmospheric heat budget analysis was large, associated with the ice concentration and synoptic situation. The turbulent heat fluxes from the open water surrounded by the sea ice are always positive (upward). However, the heat flux through sea-ice surface tends to be negative (downward) over sea-ice area associated with the relationship between the air and ice-surface temperature. Using the obtained turbulent heat fluxes and a bulk formula, relationships of turbulent heat fluxes with ice concentrations and atmospheric parameters were investigated, and a representative value of the bulk heat transfer coefficient was obtained. The estimated conditional bulk heat transfer coefficient (1:33 × 10-3) in the Sea of Okhotsk shows a smaller value than that in the Arctic region, reflecting the difference of the ice conditions, and thermal conditions in the boundary layer. Through an idea of the insulating coefficient, which measures degrees of the insulating effect of sea ice on the heat transfer, we explained that the sea ice works as a more effective insulator in weaker cold-air outbreaks. From a regression analysis, we found that the primary contribution to the amount of turbulent heat flux is the ice concentration, and second is the air temperature in the boundary layer.

Three-dimensional structure of quasi-stationary circulation anomalies observed in the course of a typical life cycle of an interannual seesaw between the surface Aleutian and Icelandic lows (AL and IL, respectively) is examined by using a reanalysis data set for the last three decades. A diagnosis is applied in a particular framework where the 31-day mean anomalies are regarded as stationary Rossby waves embedded in the zonally varying climatological-mean flow. It reveals that the upward propagation of wave activity into the stratosphere occurs in late winter primarily from the tropospheric anomalies corresponding to the anomalous IL, which develops below the entrance region of the lower-stratospheric polar night jet as a remote influence from the North Pacific. Accordingly, the North Atlantic anomalies exhibit apparent amplification and westward phase tilt with height, whereas the North Pacific anomalies are much more like the external mode. It appears that, in the presence of the zonal wavenumber 1 (k = 1) component of the climatological-mean planetary waves, the polar-night jet over the Pacific is shifted too far north to allow the stationary anomalies associated with the anomalous AL to propagate upward as stationary Rossby waves. Unlike the predominant signal of the Arctic Oscillation (or annular mode) that alters the intensity of the polar vortex, the seesaw modifies the stratospheric planetary-wave patterns in a modest but signifi-cant manner. In late winter when the AL is weaker than normal associated with a particular phase of the seesaw, the k = 1 component is masked by the enhanced zonal wavenumber 2 (k = 2) component embedded in the intensified polar-night jet. In contrast, the predominant k = 1 component embedded in the relatively weak polar-night jet dominates over the diminished k = 2 component in late winter, when the AL is stronger associated with the other phase of the seesaw. Our examination of seven late-winter major events of stratospheric sudden warming over the three recent decades suggests that the polarity of the AL-IL seesaw might set up a condition of which planetary wave component (k = 1 or k = 2) is more strongly involved in a late-winter warming event.

Through analysis of observational data for the period of 1973–94, the late-winter formation of an interannual seesaw between the surface Aleutian and Icelandic lows (AL and IL, respectively) is shown to significantly impact the covariance structure of the leading mode of the interannual variability in the geopotential height field over the extratropical Northern Hemisphere. The tropospheric leading mode for early winter (November–January) is characterized by a polar–midlatitude dipole over the Euro–Atlantic sector with a high degree of the annularity, coupled with the anomalous lower-stratospheric polar vortex. Over the North Pacific, no significant anomalies are associated with this mode. After the formation of the AL–IL seesaw, however, the dipole no longer dominates in the upper-tropospheric variability. The dipole signature is masked in late winter (February–April) by the predominant combined signature of the so-called Pacific–North American pattern and a meridional dipole over the northweste...

The seasonal dependence and life cycle of the well-known interannual seesawlike oscillation between the intensities of the surface Aleutian and Icelandic lows (AL and IL, respectively) are investigated, based on the National Meteorological Center operational analyses for the period from 1973 to 1994. It is found that the correlation between the AL and IL intensities is significantly negative only from February to mid-March. It is also found that the seesaw exhibits an equivalent barotropic structure within the troposphere. For this late-winter period an index is defined that measures the intensity difference between the two lows. A linear lag regression analysis between this index and circulation anomalies averaged in each of the nine 45-day periods from early winter to midspring reveals that the stationary AL and IL anomalies constituting the seesaw do not start developing simultaneously over the respective ocean basins in the course of a particular winter season. Rather, the seesaw formation is...

Rawinsonde observation was performed in late January through early February in 1998 around the southwestern part of the Sea of Okhotsk to estimate the turbulent fluxes of sensible and latent heat over the ice-covered ocean during the winter monsoon. Upstream cold and stable air mass originated from the Eurasian continent was significantly modified through heat and moisture supply from warm sea surface with offshore cold-air outbreaks, which consequently formed mixed layer characterized by neutral stability over downstream areas. Associated with reduction of the top of the mixed layer height through the observational period, estimated heat fluxes also decreased gradually from 210 W m-2 to 30 W m-2. These decrease tendencies of the mixed layer height and estimated heat fluxes may reflect the increase of the insulating effect of the sea-ice cover on heat and moisture exchanges between the atmosphere and ocean.

Radio sounding and in-situ observations at land-based (26 January-11 February 1998) and ship stations (4-11 February 1998) were performed over the southwestern Sea of Okhotsk covered with sea ice to estimate turbulent heat flux and investigate characteristics of thermodynamic air mass transformation processes during cold-air outbreaks. Surface heat flux estimations were carried out using two indirect methods; an atmospheric heat budget analysis using the radio sounding data at three stations and a bulk method utilizing meteorological and sea ice thickness data obtained by the ship observations. The estimated total upward turbulent heat flux over the analyzed area was approximately 100 Wm-2 even within the intense cold-air outbreak period. The height of the mixing layer associated with this small amount of the heat flux is only about 1 km, which implies that sea ice acts as an insulating material between the ocean and atmosphere and thus significantly reduces the turbulent heat fluxes. Nevertheless, the upward turbulent heat flux from the ice surface was found to be non-negligible during cold-air outbreaks and it is suggested that the sea ice grows through the sea or ice surface cooling.

Influence of sea-ice extent anomalies within the Sea of Okhotsk on the large-scale atmospheric circulation is investigated through an analysis of the dynamic and thermodynamic characteristics of the response in an atmospheric general circulation model to specified anomalous sea-ice cover. Significant response appears not only around the Sea of Okhotsk, but also downstream over the Bering Sea, Alaska, and North America in the form of a stationary wave train in the troposphere. This remote response, associated with wave activity flux emanating from the Okhotsk area to the downstream, is regarded as a stationary Rossby wave generated thermally by the anomalous turbulent heat fluxes from the ocean surface as a result of the anomalous sea-ice cover. The Pacific storm track in the model that extends zonally at 35°N is located too far south of the Sea of Okhotsk to exert substantial feedback forcing on the local and remote response. Since a similar stationary wave train is identified in the composite di...

An atmospheric general circulation model was used to investigate the influence of Okhotsk sea ice on large-scale atmospheric circulation. Significant differences in the model responses between heavy and light ice cover are evident not only around the Sea of Okhotsk but also downstream towards North America in the form of a stationary wavetrain in the troposphere. Because the wave activity flux associated with the wavetrain emanates downstream from the Sea of Okhotsk, this remote response is regarded as a stationary Rossby wave excited thermally through an anomalous surface heat flux over the Sea of Okhotsk. The wavetrain is thermally reinforced downstream by the anomalous heat flux associated with wind anomalies over the ocean surface, which are induced by the wavetrain itself.

We investigated the interannual variation of the sea ice over the Sea of Okhotsk by using radar observation data and gridded ice-coverage data for the years 1969-1994. It became evident that the abrupt decrease of sea ice over the southern part of the Sea of Okhotsk occurred in 1989, and that this reduced-ice condition has continued since then. In addition, the winter time Aleutian low has abruptly weakened since 1989. According to the lag-correlation analysis, this weakening has brought about the reduction in extent of the ice-coverage.

Variations of air temperature in Hokkaido during winter are characterized by the presence of two minima in ten-day normals; days 21-30 (end of January) and days 41-50 (middle of February). We name this tendency the "W-phenomenon", which is significant in the northern coastal area of Hokkaido facing the Sea of Okhotsk. The second minimum occurs when the ice cover is most extensive along the Okhotsk coast of Hokkaido. We examine this relation using rotated principal component analysis (RPCA). The RPCA results show that the second mode is a factor of the ice cover that is related to the second minimum. However, the correlation coefficient between rotated principal components of the second mode and ice concentration is rather low, -0.56. The RPCA results also show that the wind field is another factor that governs the "W-phenomenon". The relationship between the rotated principal components and wind directions shows that the drop in temperature in Hokkaido is associated with not only heavy ice cover but also northeasterly wind. Two mechanisms of the northeasterly wind system are expected : weak winds from an anticyclone over Okhotsk ice cover off Hokkaido and strong winds from a cyclone over the Pacific Ocean off the southeast coast of Hokkaido. Both these cases are possibly caused by the heavy ice cover in the Sea of Okhotsk. In the former mechanism, the wind directly carries cold air flow cooled over the sea ice. In the latter, the heavy ice cover prevents cyclones from moving into the Sea of Okhotsk.

1992年8月17日から30日までの間, グリーンランド海における国際共同観測に参加した。ノルウェーの観測船R/V LANCEに同国のほか, ドイツ, イギリス, 米国, 日本から計5カ国17名の研究者が乗船し, 係留系の設置・回収, 採水, CTD観測などを実施した。日本側は水温観測を担当し, 流氷縁から東方の海域(77°～79°N, 3°W～15°E)2測線53点において水温の鉛直分布を測定した。流氷縁やスピッツベルゲン島近海では, 氷塊の融解や陸水の流入に起因すると考えられる複雑な水温構造が形成されていた。, Oceanographic observations in the Greenland Sea were conducted as a part of an international cooperative program. Seventeen scientists from five countries (Norway, Germany, England, U.S.A. and Japan) participated in the R/V LANCE cruise from August 17 to 30,1992. Mooring work, CTD measurements, water sampling and others were carried out both in the ice-covered and open sea. Temperature profiles from XBT casts were obtained at 53 points. The thermal structure of the eastern Greenland Sea seems to be strongly influenced by ice melting near the ice edge and land-water influx from Spitsbergen.

Climate Dynamic Geophysical Mon Copyright 2010 b 10.1029/2008GM Structure and dynamics of the Northern Hemisphere planetary waves, which cause geographically fixed longitudinal dependence to the climate, are examined through dynamical diagnoses applied tomodern global data sets. Summertime planetarywave signature in the Western Hemisphere includes surface maritime subtropical anticyclones, for which pronounced land-sea thermal contrasts across the west coasts of subtropical continents are important as thermal forcing. Its Eastern Hemisphere counterpart is dominated by continental-scale cyclone and anticyclone in the lower and upper troposphere, respectively, associated with Asian monsoon. Wintertime planetary waves are forced orographically and thermally in middle/subpolar latitudes, with pronounced land-sea thermal contrasts, including a contribution from diabatic heating along oceanic “storm tracks.” Wave activity thus generated propagates southeastward, maintaining an upper-level vorticity dipole over the Atlantic with an eddy-driven polar-front jet (PFJ) separated from a subtropical jet (STJ). Its Pacific counterpart is in the opposite sense with a predominant single jet with PFJ-STJ hybrid characteristics. Stationary circulation anomaly patterns that cause regional climate variability are strong in winter over the midlatitude ocean basins, extracting kinetic energy effectively from diffluent westerly jets and with feedback forcing by transient eddies along storm tracks. In the summertime Asian STJ exit, a stationary baroclinic anomaly pattern is dominant, maintaining itself by extracting potential energy from the jet and negating it by anomalous cumulus activity. Each of these patterns thus bears characteristics of a dynamical mode. Generation of shallow, cold surface anticyclones is discussed from a viewpoint of interaction of stationary Rossby waves with surface baroclinic zones.

[1] Influence of low Arctic sea-ice minima in early autumn on the wintertime climate over Eurasia is investigated. Observational evidence shows that significant cold anomalies over the Far East in early winter and zonally elongated cold anomalies from Europe to Far East in late winter are associated with the decrease of the Arctic sea-ice cover in the preceding summer-to-autumn seasons. Results from numerical experiments using an atmospheric general circulation model support these notions. The remote response in early winter is regarded as a stationary Rossby wave generated thermally through an anomalous turbulent heat fluxes as a result of anomalous ice-cover over the Barents-Kara Seas in late autumn, which tends to induce an amplification of the Siberian high causing colder conditions over the Far East. The late-winter cold anomalies over Eurasia are also reproduced in our experiment, which is associated with the negative phase of the North Atlantic Oscillation.

An analysis of satellite sea-ice records for recent decades reveals a highly coherent spatial and temporal structure of the Northern Hemisphere (NH) wintertime sea-ice variability and its close link to anomalous atmospheric circulation. The dominant mode of the wintertime sea-ice variability is characterized by a double-dipole composed of one dipole over the North Atlantic and the other over the North Pacific, which are mutually correlated interannually. This dominant sea-ice mode is lag correlated with the winter-averaged North Atlantic Oscillation (NAO) index at lags up to two winters when the NAO leads. In the sub-Arctic, significant lead–lag relationships exist between sea-ice extent (SIE) anomalies on regional scales, which are closely associated with atmospheric circulation anomalies. An eastward evolving pattern is identified in regional SIE anomalies from the Labrador to Nordic and farther to the Okhotsk Sea at multi-year time-scales, led by anomalously weak Aleutian and strong Icelandic lows. The results suggest the presence of climate memories over the North Atlantic and Eurasia, which are crucial for recent downward trends in the NH SIE by transforming atmospheric influences into slower changes in sea-ice conditions. The summer Okhotsk high, which leads to a sea-ice reduction along the east Siberian coast and further affects sea-ice conditions over the Arctic Ocean, is a key link between summer Arctic and winter sub-Arctic sea-ice trends. We also conjecture that variations and changes in the NH sea-ice conditions are linked to climate variability in the tropics.

[1] Time-series observations of optical fields in the euphotic layer and particle fluxes at 150 m were made in the western North Pacific for half year of 2005. The ratio of surface photosynthetically available radiation (surface PAR) to in situ quantum irradiance at ca. 40 m (in situ QI), as an index of turbidity, began to increase in the middle of April, peaking between the end of June and the middle of July. Seasonal variability in the ratio of spectral irradiance at a wavelength of 555 nm to that at 443 nm (Ed(555)/Ed(443)) at 40 m, as an index of chlorophyll abundance, synchronized well with the surface PAR/in situ QI ratio. Organic carbon flux also increased between the end of June and the middle of July and correlated well with optical variability. This result suggests that primary produced carbon in the euphotic layer was quickly transported to the ocean interior. Using the Ed(555)/Ed(443) and an empirical equation from shipboard observations, primary productivity was estimated to be ca. 300 mgC m−2 day−1 on average. Assuming that trapping efficiency was only 20% and organic carbon flux decreased drastically between 100 m and 150m, the export ratio at 100 m was estimated to be ca. 30 ± 10%, which is significantly higher than that in other oceans.

[1] An intra-seasonal relationship, including a possible feedback, is investigated between the North Atlantic Oscillation (NAO) and a hemispheric-scale seesaw-like pattern dominant in sea ice variability over the wintertime Northern Hemisphere, with one polarity in the Bering and Labrador Seas and the other in the Okhotsk and Greenland-Barents Seas. Statistical analysis using observational data suggests that a particular phase of NAO and anomalous atmospheric circulation in the Pacific during early winter contribute toward the development of the midwinter hemispheric sea-ice seesaw. In contrast, the ice seesaw tends to damp the preexisting NAO signal during late winter, indicating a reversal of the phase relation between them. This NAO damping may be triggered by the Pacific sea-ice anomalies. Results from numerical experiments generally support this notion and further suggests a stationary Rossby wave train emanated from the North Pacific as a dynamical mechanism for damping the NAO signal.

and high latitudes. Conversely, Thompson and Lorenz [2004] attempted to detect the effects of both hemispheric annular modes (AMs) on the tropics. They showed coupling between the AMs and tropical atmosphere and that a wintertime positive (negative) AM generates the upper tropospheric zonal mean westerly (easterly) anomalies in the tropics after a 2-week lag. These results suggest a link between the NAM and tropical variability. However, they did not note any direct influences of the NAM on the ENSO. [3] This study examined the influences of NAM on the ENSO. Based on the results of previous studies, we examined the lead and lag relationships between the NAM and ENSO in all seasons using a reanalysis data set. The observational evidence revealed a statistically significant relationship between the NAM signature and the ENSO. To strengthen this finding, we also used an atmospheric general circulation model (AGCM) to simulate climatological monthly mean sea surface temperature (SST) distributions.

A warmer Arctic climate is influencing air pressure over the North Pole and wind patterns over the Northern Hemisphere. In response, recent data and modeling suggest that more cold and snowy winters can be expected in Europe, eastern Asia, and eastern North America. These were some of the issues discussed at the International Polar Year (IPY) conference, the largest polar science meeting ever held, with more than 2400 attendees. More than 80 scientific papers debated the state of the science regarding Arctic amplification and midlatitude connections. Arctic amplification is just that: The Arctic is warming twice as fast as the rest of the planet, caused by unique physical processes related in part to loss of sea ice. Arctic amplification is also a consequence of changes in atmospheric circulation that are anthropogenically forced, part of chaotic variability, or both.

An analysis of satellite sea-ice records for recent decades reveals a highly coherent spatial and temporal structure of the Northern Hemisphere (NH) wintertime sea-ice variability and its close link to anomalous atmospheric circulation. The dominant mode of the wintertime sea-ice variability is characterized by a double-dipole composed of one dipole over the North Atlantic and the other over the North Pacific, which are mutually correlated interannually. This dominant sea-ice mode is lag correlated with the winter-averaged North Atlantic Oscillation (NAO) index at lags up to two winters when the NAO leads. In the sub-Arctic, significant lead–lag relationships exist between sea-ice extent (SIE) anomalies on regional scales, which are closely associated with atmospheric circulation anomalies. An eastward evolving pattern is identified in regional SIE anomalies from the Labrador to Nordic and farther to the Okhotsk Sea at multi-year time-scales, led by anomalously weak Aleutian and strong Icelandic lows. The results suggest the presence of climate memories over the North Atlantic and Eurasia, which are crucial for recent downward trends in the NH SIE by transforming atmospheric influences into slower changes in sea-ice conditions. The summer Okhotsk high, which leads to a sea-ice reduction along the east Siberian coast and further affects sea-ice conditions over the Arctic Ocean, is a key link between summer Arctic and winter sub-Arctic sea-ice trends. We also conjecture that variations and changes in the NH sea-ice conditions are linked to climate variability in the tropics.