Ice thickness variability in the Arctic Ocean between 1954–1990, results from a coupled ocean-ice-atmosphere column model

The interannual variation of the Arctic Ocean ice thickness during the period 1954–1990 is investigated by using a coupled ocean-ice-atmosphere column model. The model is forced by poleward energy flux in the atmosphere from NCEP/NCAR reanalysis data, ice export from satellite observations, cloudiness, and precipitation observed at the Russian North Pole drift stations. During the period 1977–1986 the model ice thickness decreased from 3.2 m to 2.0 m. The decrease is mainly caused by extra melting due to larger poleward energy flux in summer, and reduced ice growth in winter as a result of both increased cloudiness and energy flux. Precipitation and ice export are of less importance. A sensitivity study shows that the NCEP/NCAR data is accurate enough with respect to stochastic errors to ensure that the thinning is not caused by forcing errors. It is also shown that the poleward energy flux during summer is the dominant factor for regulating the ice thickness. The column model gives different results compared to other model studies using 2D ice models, especially towards the end of the period. Possible reasons for this disparity are discussed.     

Are Cosmic Rays Influencing Oceanic Cloud Coverage – Or Is It Only El Niño?

The monthly average (C2) cloudcoverage data produced by the International SatelliteCloud Climatology Project (ISCCP) for the period ofJuly 1986–June 1991 show strong global and regionalcloud coverage variations associated with the ElNiño of 1986–1987. The Pacific Ocean, inparticular, shows strong regional variations in cloudcoverage. These agree well with contemporaneoussatellite observations of broadband shortwave infraredcloud forcing measured by the Earth Radiation BudgetExperiment. Svensmark and Friis-Christensen (1997)noted a similarity between the shape of the timeseries curve of average cloud coverage fraction formid- to low-latitude ocean-areas and the time seriescurve of cosmic ray flux intensity. They proposed acausal relationship – a `missing link' for solarcycle influence on Earth climate. Further spatial andtemporal analysis of the same ISCCP C2 data in thispaper indicates that the cloud coverage variationpatterns are those to be expected for the atmosphericcirculation changes characteristic of El Niño,weakening the case for cosmic rays as a climaticforcing factor.     

Multicentury reconstruction of the Canadian Drought Code from eastern Canada and its relationship with paleoclimatic indices of atmospheric circulation

Inter-annual and -decadal scale variability in drought over the Abitibi Plains ecoregion (eastern Canada) was investigated using a 380-year dendroclimatic reconstruction of the Canadian Drought Code (CDC; July monthly average) i.e., a daily numerical rating of the average moisture content of deep organic layers. Spectral analyses conducted on the reconstructed CDC indicated a shift in spectral power after 1850 leading toward a reduction in interdecadal variability and an increase in interannual variability. Investigation on the causes for this shift suggested a decrease in North Pacific forcing after the mid-nineteenth century. Cross-continuous wavelet transformation analyses indicated coherency in the 8–16 and 17–32-year per cycle oscillation bands between the CDC reconstruction and the Pacific Decadal Oscillation (PDO) prior to 1850. Following 1850, the coherency shifted toward the North Atlantic Oscillation (NAO). Principal component analysis conducted over varying time windows reaffirmed that the Pacific forcing was restricted to the period about 1750–1850. Prior to and after this period, the CDC was correlated with the NAO. The shift around 1850 could reflect a northward displacement of the polar jet stream induced by a warming of the sea surface temperature along the North Pacific coast. A northward displacement of the jet stream, which inhibits the outflow of cold and dry Arctic air, could have allowed the incursion of air masses from the Atlantic subtropical regions.     

Climatology of deep cyclones over Asia and the Northwest Pacific

Summary A frequency analysis of deep cyclones with central pressure less than or equal to 990 hPa over Asia and the Northwest Pacific in the period 1958–1989 is presented. The most active areas of deep cyclones are: 1) Western Siberia, east of the Ural Mountains; 2) Northeastern China, east of the Mongolia Plateau and, 3) South-west of the Kamchatka Peninsula. The first most active area is related to European cyclones (Schinke, 1993) and starts in the lee of the Ural Mountains; the second is related to cyclones in the lee of Altai-Sayan and the third to East Asian coastal cyclones. After zonal averaging, two frequency maxima of deep cyclones emerged, one between 62.5–67.5° N and the other between 47.5–52.55° N. This is different from the European and North Atlantic regions where only one maximum occurs. The seasonal frequency deep cyclones in Northeastern China reaches maximum in spring and summer while in western Siberia and the Northwest Pacific deep cyclones are more frequent in winter. The annual trend of deep cyclones over the Northwest Pacific shows an increase from the sixties to the eighties while deep cyclones over East Asia decreased during this period. In the 1980's, more deep cyclones occurred over the Northwest Pacific and less deep cyclones over main land Asia which may be associated with the northern hemisphere warming. The monthly number of oceanic deep cyclones in December and January appeared to be positively correlated with the August and September sea surface temperatures over the East Pacific (El Nino regions 1 + 2).With 7 Figures     

华北夏季降水地域特征的旋转主分量研究及其相关分析

用旋转主分量(RPC)方法,研究华北降水的空间分布特征.给出了华北降水空间分布的RPC的前10个模态.它们概括了华北地区降水的基本特征及历史上的大旱和大涝年的地域分布.每一种降水模态的时间系数都表现出了长周期的年代际变化的规律.华北发生大旱与大涝的最可能的分布是模态3、4与模态10.如1965、1968和1983年的大旱;1963和1973年的大涝年等.分析了各个模态与太平洋副热带高压强度、东亚环流指数、前冬赤道东太平洋海温、以及江淮流域降水的相关表明:它们之间的相关都有各自的最佳模态.如对赤道东太平洋海温与太平洋副热带高压强度而言,最佳模态的特征是:当海温呈El Nino型和西太副高偏强时,华北降水的最可能分布是东部沿海为强的干旱区,其余地区降水皆偏多.与江淮流域降水和EAP流型的相关则主要以1954、1980及1991年为代表的第1和第9模态为主要形态.它们与华北降水有极好的反相关.     

Air–Sea Flux Estimates And The 1997–1998 Enso Event

Bulk formulae for wind stress, sensible and latent heat flux are presented that are suitable for strong mesoscale events such as westerly wind bursts that contribute to the El Niño-Southern Oscillation (ENSO). Their exchange coefficients for heat and momentum have a simple polynomial dependence on wind speed and a linear dependence on air–sea temperature difference. The accuracy of these formulae are validated with respect to air–sea fluxes estimated using the standard algorithm adopted by the Tropical Ocean-Global AtmosphereCoupled-Ocean Atmosphere Response Experiment (TOGA COARE). The comparison ismade for observations from 96 Tropical Atmosphere Ocean (TAO) array and National Oceanographic Data Center (NODC) moorings in the equatorial and North Pacific Ocean spanning years 1990–1999. The bulk formulae are shown to have very small median root–mean-square differences with respect to the TOGA COARE estimates: 0.003 N m^-2, 1.0 W m^-2, and 10.0 W m^-2 for the wind stress, sensible heat flux, and latent heat flux, respectively.The variability of air–sea fluxes during the 1997–1998 ENSO is also examined, along with a possible relationship between air–sea fluxes and surface ocean mixed layer depth (MLD). The wind stress and latent heat flux during the 1997 El Niño are found to be greater in the warm pool of the western Pacific than in the central Pacific where the ENSO is most clearly seen. These differences disappear upon the start of La Niña. The MLD in the equatorial Pacific is found to be moderately correlated to air–sea fluxes just before the start of the 1998 La Niña and poorly correlated otherwise.     

Gulf of Alaska Atmosphere-Ocean Variability Over Recent Centuries Inferred from Coastal Tree-Ring Records

Eight tree-ring chronologies from coastal sites along the Gulf of Alaska (GOA) are used to develop a 227-year (1762–1988) reconstruction of spring/summer (March–September) coastal land temperatures for the region. This reconstruction explains 35% of the variance in the instrumental temperature data. The tree-ring records and reconstruction reflect the documented 1976 transition from cold to warm conditions in the North Pacific and are consistent with regional temperature compilations. Three of the eight ring-width series, from elevational timberline sites where trees are particularly stressed by temperature, extend back to A.D. 1600 and are used to identify additional occurrences of such transitions. The first principal component (PC) scores of these three longer records are positively correlated with spring (March–May) land and sea surface temperatures for the GOA region and are used to reconstruct land surface temperatures. Decadal-scale fluctuations in the reconstructions show agreement with decade-long changes in the intensity of the Aleutian Low pressure cell over the past century, suggesting that the tree-ring data may provide an index of past circulation changes for the northeast Pacific. Blackman-Tukey spectral analyses of both reconstructions indicate significant power at 7–11 years, with additional peaks at 3 years for the spring/summer reconstruction and 19 years for the longer spring temperature series. The modes of variation at about 3 and 7 years may correspond to those associated with the El Niño-Southern Oscillation bandwidth, whereas the 19-year term may relate to a proposed 20-year cycle of North Pacific circulation. The spring temperature series shows generally increased growth over the past century, coinciding with warmer spring temperatures in south coastal Alaska over this interval. Comparison with the entire spring series suggests that the recent warming exceeds temperature levels of prior centuries, extending back to A.D. 1600.     

Simulation of the 2014 Anomalous Warming in the Northeast Pacific

The Nucleus for European Modelling of the Ocean (NEMO) numerical model was used to simulate the North Pacific Ocean beginning in January 1960. The model had a horizontal resolution of 0.25^o, 46 vertical levels, and employed a spectral nudging assimilation scheme that, unlike standard nudging, nudges only specific frequency and wavenumber bands. This simulation was nudged to the mean and monthly Levitus climatology of potential temperature and salinity. The model was forced with mean monthly winds, net heat flux, and precipitation from the National Centers for Environmental Prediction (NCEP). The simulation was used to study a recent intrusion of much warmer and less saline water than normal from the west into the Gulf of Alaska, beginning in December 2013 and lasting until at least the early summer of 2014. The observed surface temperature anomalies were more than 4 standard deviations above normal. The model reproduced these anomalies in both a qualitative and quantitative manner, reproducing the same scale of anomalies over the region. An anomalous increase in the North Pacific Current (NPC) was found in the model in 2012 and the beginning of 2013, in agreement with observations. This increase in the NPC is associated with the positive phase of the North Pacific Gyre Oscillation. The causes of the temperature anomalies in the Gulf of Alaska could be due to three key factors: (i) an anomalously high, positive, surface heat flux in 2013 over the greater North Pacific; (ii) a significant decrease in the eastward flow of the NPC starting in late 2013 (with an accompanying decrease in cold water advection) after a period of historically strong eastward flow; and (iii) weaker winds throughout most of 2013 accompanied, however, by a shift to stronger northward winds (with an accompanying increase in warm water advection) in late 2013.     

Interdecadal variability of the Pacific Ocean: model response to observed heat flux and wind stress anomalies

Variability of the Pacific Ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux, wind stress and turbulent kinetic energy (TKE) over the period 1970-88. The model captures the 1976-77 winter time climate shift in sea surface temperature, as well as its monthly, seasonal and longer term variability as evidenced in regional time series and empirical orthogonal function analyses. Examination of the surface mixed-layer heat budget reveals that the 1976-77 shift was caused by a unique concurrance of sustained heat flux input anomalies and very strong horizontal advection anomalies during a multi-month period preceding the shift in both the central Pacific region (where cooling occurred) and the California coastal region (where warming occurred). In the central Pacific, the warm conditions preceding and the cold conditions following the shift tend to be maintained by anomalous vertical mixing due to increases in the atmospheric momentum flux (TKE input) into the mixed layer (which deepens in the model after the shift) from the early 1970s to the late 1970s and 1980s. Since the ocean model does not contain feedback to the atmosphere and it succeeds in capturing the major features of the 1976-77 shift, it appears that the midlatitude part of the shift was driven by the atmosphere, although effects of midlatitude ocean-atmosphere feedback are still possible. The surface mixed-layer heat budget also reveals that, in the central Pacific, the effects of heat flux input and vertical mixing anomalies are comparable in amplitude while horizontal advection anomalies are roughly half that size. In the California coastal region, in contrast, where wind variability is much weaker than in the central Pacific, horizontal advection and vertical mixing effects on the mixed layer heat budget are only one-quarter the size of typical heat flux input anomalies.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil     

Resource use and resource efficiency in the Asia–Pacific region

Over the last few decades, the Asia–Pacific region has experienced the most dynamic economic development of any of the world's regions, leading to a rapid increase in resource use and associated emissions. The region is now a major driver towards overshooting global resource use limits. In this paper, we provide an estimate of material use and resource efficiency in the Asia–Pacific region and its sub-regions for the first time, to complement existing knowledge on global resource use. We show that the Asia–Pacific has become the single largest user of resources globally, and that the efficiency of resource use in the region decreased over the period 1970–2005. Furthermore we show that the region's share of total resource use is now so significant that decreasing resource efficiency there has driven a decrease in overall global resource efficiency, for the first time in a century. Using an IPAT framework we found that rising per capita incomes contributed more strongly to growing material use than did population growth. Technology did not moderate material use growth to the extent expected. We argue that a failure to make these issues a central and immediate focus of public policy in the Asia–Pacific region would compromise competitiveness, resource security, and poverty reduction in the region over the medium to long term.     

Estimates of effective aerosol optical depths from spectral solar radiation measurements

Summary This study reports a 37-year long record of direct beam spectral irradiance measurements made in Athens, Greece. An analysis of aerosol effects on the spectral distribution of solar radiation through effective optical depths, are presented. Thus, spectrally resolved aerosol optical depths were calculated and analyzed for the period 1954–1990. Summertime aerosol optical depths were found to be larger than winter values, while their seasonal variations were related to varying weather conditions throughout the year. The interrelationships between effective optical depths were found to be linear and were related strongly to microphysics of aerosol loading in the atmosphere. For the period 1962–1983 as wavelength exponent ₀ values ranged between 0.76–1.14 the spectrally resolved optical depths were found to increase markedly with respect to remaining periods 1954–1961 and 1984–1990 in which ₀ values ranged between 1.16–1.39. A minimum in aerosol optical depths, believed to be near background levels, was reached during period 1954–1957, while there was some indication that both optical depths continued to decrease reaching background levels at the end of the study period. From the long-term variation of aerosol effective optical depths some interesting information on the time evolution of air quality in Athens was gained. In addition, their frequency distribution, temporal daily variations and some remarks on photosynthetically active radiation for plant development, are presented and discussed.With 7 Figures     

The periodicity of storm surges in the Bering Sea from 1898 to 1993, based on newspaper accounts

Spectral analysis of 96 yr of Bering Sea storm records reported in the Nome News (1899–1903) and Nome Nugget (1901–1993) newspapers indicate regularities in the 11-, 5–7- and 3-yr periods. Statistical tests on the 11-yr period found no statistically significant correlation with sunspot cyclicity despite a tendency toward maximum storminess during low sunspot periods. The 3- and 5–7-yr cycles may correlate with variability in the El Niño Southern Oscillation and easterly shifts in the mean position of North Pacific low pressure anomalies. Storm surges were infrequent from 1916 to 1928 and 1947 to 1959, while the most frequent and intense storms hit during 1900–1913, 1936–1946, 1974–1976 and in 1992.     

Emission and flux of DMS from the Australian Antarctic and Subantarctic Oceans during the 1988/89 summer

DMS emissions and fluxes from the Australasian sector of the Antarctic and Subantarctic Oceans, bound by 46–68° S and 65.5–142.6° E, were determined from a limited number of samples (n=32) collected during three summer resupply voyages to Australian Antarctic continental research bases between November 1988 and January 1989 (a 92 day period). The maximum DMS emission from this sector of the Antarctic Ocean was in an area near the Antarctic Divergence (60–63° S) and the minimum DMS emission was from the Antarctic coastal and offshelf waters. The greatest emission of DMS from this sector of the Southern Ocean was from the Subantarctic waters. DMS flux from the Australasian Antarctic Ocean was 64.3×10⁶ (±115) mol d^–1 or 5.9 (±10.6)×10⁹ mol based on an emission of 10.9 (±19.5) µmol m^–2 d^–1 (n=26). The flux of DMS from the Australasian sector of the Subantarctic Ocean was probably twice the flux of DMS from the adjacent Antarctic Ocean.     

Antarctic sea-ice relationships with indices of the atmospheric circulation of the Southern Hemisphere

A link between the Antarctic sea-ice extent and low-frequency atmospheric variations, particularly ENSO, has been suggested by recent modeling and empirical studies. This question is examined here using a high-resolution (by week, by region) data base of Antarctic sea-ice extent for the 1973–1982 period. Although of relatively short duration by Northern Hemisphere standards, such a data base offers an opportunity rare in Southern Hemisphere climate studies. The seaice variations are examined in the context of longer-term indices of the large-scale atmospheric circulation. These are a Southern Oscillation Index (SOI) and an index of sea-level pressure (SLP) wavenumber one in the Southern Hemisphere extratropics. The indices are updated through 1982, and their associations with regional-scale pressure indices in the Australia-New Zealand sector are also examined. The 1973–1982 period is anomalous when compared with the period 1951–1972. Correlation analysis of the monthly sea ice and circulation index values reveals that much of the apparent link between the ice and the SOI suggested in previous studies arises from autocorrelations present in both data sets and the strong annual cycle of sea-ice extent. Removing these effects from the data and re-running the correlations reveals that most of the resulting significant associations between the ice and one or other of the circulation indices can probably be explained on the basis of chance. In order to reconcile these findings with previous studies that show some strong ice-circulation interactions on regional scales, only those months in which significant correlations occur between both largescale circulation indices and the sea ice are examined further. These occur preferentially in the Ross and Weddell sectors, which constitute the regions contributing most to the variability of Antarctic sea ice. The analysis suggests that the sea-ice-extent changes lag the SOI by several months but may precede changes in extratropical SLP wavenumber one. Confirmation of these tentative regional ice extent-circulation teleconnections necessarily awaits the forward extension of the high-resolution sea-ice data base beyond the 10 years available here.This paper is based on material presented at the Conference on Mechanisms of Interannual and Longer-Term Climatic Variations held at the University of Melbourne, Australia: December 8–12, 1986.     

Abrupt change in climate regime from summer to fall 1985 and stability in the fall

Summary This paper treats a dramatic transition between the summer and fall of 1985 when temperature and precipitation anomaly patterns and the associated midtropospheric flow over the coterminous United States and adjacent oceans underwent a strong reversal. After this break in regime, the fall patterns locked into a remarkably stable state. It is interesting that this case confirms a more general statistical result from previous completely independent episodes. The hypothesis suggested to explain this strong change and its subsequent persistence draws upon air-sea interactions over the North Pacific and resulting downstream influences.With 11 FiguresPresented at Eleventh Diagnostic Workshop in Urbana, Illinois, U.S.A. on October 14–17, 1986.     

Interannual variability of the surface heat budget over the northern North Atlantic and North Pacific Oceans

Summary The January anomaly time series for each term of the surface heat budget (solar and longwave radiation, sensible and latent heat fluxes) are calculated for Ocean Weather Stations (OWSs) in the North Pacific and North Atlantic Oceans. The data set used is the Comprehensive Ocean-Atmosphere Data Set (COADS). The dominant term is the latent heat flux. The results for OWS P in the northern North Pacific show that the interannual variability of the heat budget parameters is correlated with the synoptic variability of the Aleutian low. There is also an interdecadal signal present in the heat budget anomaly time series, with the sign of the anomaly persisting for about 8–10 years. In contrast, for OWS J in the northern North Atlantic, no correlation is found between the variability of the heat budget parameters and the corresponding synoptic variability of the Icelandic low. The station J air-sea heat fluxes also show a higher frequency variability, compared to those of station P. The results suggest the variability of the January air-sea heat exchange processes are fundamentally different over the two ocean basins.With 3 Figures     

太平洋海气CO2通量对气候事件的响应

应用一个嵌套了海洋生物地球化学循环的太平洋环流碳循环模式,分析了1960～2000年太平洋不同海区海气碳通量随时间的变化。模拟结果显示,赤道太平洋为大气CO₂的排放区,南、北太平洋(南、北纬15°至模式计算区域南、北边界)为吸收区。3个海区海气碳通量随时间均存在显著的波动,其中赤道太平洋海气碳通量年际波动最显著。3个海区海气碳通量年际波动对气候事件的响应并不一致,在El Niño年赤道太平洋冷舌的强度和总溶解无机碳(DIC)的浓度以及输出生产力均会受到上升流减弱的影响而降低,La Niña年这些海气碳通量控制要素的分布情况则正好相反,但在南北太平洋副热带以及高纬度海区,El Niño和La Niña对这些要素带来的影响却并不一定相反,对输出生产力的影响甚至是一致的。以海表温度(SST)为例考察海气碳通量与物理场之间的关系表明,在赤道太平洋上升流对DIC的影响是控制海气碳通量变化的主要因素,而在其他海区,尤其是副热带海区,由于垂直运动的年际变化较小,且生物生产力水平较低,SST的波动对海气碳通量年际变化的影响更加重要。     

A hybrid technique for computing the monthly mean net longwave surface radiation over oceanic areas

Summary Global maps of the monthly mean net upward longwave radiation flux at the ocean surface have been obtained for April, July, October 1985 and January 1986. These maps were produced by blending information obtained from a combination of general circulation model cloud radiative forcing fields, the top-of-the-atmosphere cloud radiative forcing from ERBE and TOVS profiles and sea surface temperature on ISCCP C1 tapes. The fields are compatible with known meteorological regimes of atmospheric water vapor content and cloudiness. There is a vast area of high net upward longwave radiation flux (> 80 W m^–2) in the eastern Pacific Ocean throughout most of the year. Areas of low net upward longwave radiation flux (< 40 Wm^–2) are the tropical convective regions and extra tropical regions that tend to have persistent low cloud cover. The technique used in this study relies on GCM simulations and so is subject to some of the uncertainties associated with the model. However, all input information regarding temperature, moisture and cloud cover is from satellite data having near global coverage. This feature of the procedure alone warrants its consideration for further use in compiling global maps of the net longwave radiation at the surface over the oceans.With 9 Figures     

北太平洋海表温度与500hPa西太平洋副高和极涡相互作用的统计分析

本文采用斜交PROMAX因子分析方法分析了1954—1986年北太平洋逐月海表温度与500hPa西太平洋副高和极涡环流指数(7个因子)的相互关系,指出(1)500hPa西太平洋副高和极涡指数与北太平洋海温的相关值存在明显的年变化,以赤道太平洋区最敏感,(2)赤道东太平洋海表温度的变化与10个月前的极涡中心强度、同期和1—3个月前西太平洋副高面积、强度、位置变化有联系,(3)500hPa西太平洋副高面积和强度的变化受到前3—5个月赤道东太平洋和3个月前赤道中太平洋海表温度的影响,500hPa西太平洋副高位置与前3—5个月赤道东太平洋海表温度有联系.