Climate Change in the Subtropical Jetstream during 1950–2009   总被引：1，自引：0，他引：1  

B. Abish  P. V. Joseph  Ola. M. Johannessen 《大气科学进展》2015,32(1):140-148

A study of six decades(1950–2009) of reanalysis data reveals that the subtropical jetstream(STJ) of the Southern(Northern) Hemisphere between longitudes 0°E and 180°E has weakened(strengthened) during both the boreal winter(January,February) and summer(July, August) seasons. The temperature of the upper troposphere of the midlatitudes has a warming trend in the Southern Hemisphere and a cooling trend in the Northern Hemisphere. Correspondingly, the north–south temperature gradient in the upper troposphere has a decreasing trend in the Southern Hemisphere and an increasing trend in the Northern Hemisphere, which affects the strength of the STJ through the thermal wind relation. We devised a method of isotach analysis in intervals of 0.1 m s-1in vertical sections of hemispheric mean winds to study the climate change in the STJ core wind speed, and also core height and latitude. We found that the upper tropospheric cooling of the Asian mid-latitudes has a role in the strengthening of the STJ over Asia, while throughout the rest of the globe the upper troposphere has a warming trend that weakens the STJ. Available studies show that the mid-latitude cooling of the upper troposphere over Asia is caused by anthropogenic aerosols(particularly sulphate aerosols) and the warming over the rest of the global mid-latitude upper troposphere is due to increased greenhouse gases in the atmosphere.  相似文献   

Fisheries rent creation and distribution—the imaginary case of Codland     

Ola Flaaten 《Marine Policy》2010

This paper discusses actual and possible achievements and failures of Codland and examines it from the point of view of efficiency and in terms of distribution. Joint analysis of the two approaches is needed when contemplating fisheries management reforms, since such reforms may create both winners and losers. The analysis demonstrates how rent drain from fishing communities and countries may occur despite significant resource rent creation. The change in the Codland economy is illustrated and compared to that of actual countries and to resource economic theory. It is concluded that if distributional and equity objectives matter, other instruments than ITQs, such as conditional tradeable fish quotas and vessel licences, resource taxes, co-management, public ownership, auctions, leases, time limited rights, time and area regulations, territorial user rights (TURFs) and marine protected areas (MPAs), should also be used.  相似文献   

Interannual variability in water masses in the Greenland Sea and adjacent areas   总被引：1，自引：0，他引：1  

Genrich V. Alekseev  Ola M. Johannessen  Alexander A. Korablev  Vladimir V. Ivanov  Dmitry V. Kovalevsky 《Polar research》2001,20(2):201-208

Oceanographic data covering the period 1950–1998 are used to determine interannual variations in the convection intensity and water mass structure in the Greenland Sea and adjacent areas. Extremely cold winters throughout 1965–1970 assisted intensification of the water vertical exchange in the Greenland and Norwegian seas. As a result, cold and fresh Greenland Sea Deep Water (GSDW) production was extremely high in the central Greenland Sea while in the southern Norwegian Sea warm and salty water spread downwards. The recent rapid warming in the Greenland Sea Gyre interior from 1980 originates, we argue, from an increase in the Atlantic Water (AW) temperature due to the advection of warm waters into the region with the Return Atlantic Current. The negative water temperature and salinity trends in the upper 300 m layer of the Atlantic Water in the Norwegian Sea prevailed during 1950–1990, whereas during 1980–1990 the water temperature trends are indicative of warming of that layer. Observation series obtained onboard the Ocean Weather Ship Mike confirmed the existence of layers with advectiondriven high oxygen concentrations in intermediate and deep layers. The depth of oxygen maxima and the values of oceanographic parameters at this horizon can be regarded as indicators of the convection intensity in the Arctic domain. A simultaneous rise in NAO index and GSDW temperature points to a link between atmospheric and thermohaline circulation. Weakening in water exchange with the North Atlantic could be the reason for the Polar Water recirculation increase within the Nordic seas.  相似文献   

Physico/chemical stability of smectite clays     

Roland Pusch  Ola Karnland 《Engineering Geology》1996,41(1-4):73-85

There is convincing evidence from field data that smectite clay undergoes conversion primarily to illite and chlorite if it is fully water-saturated and heated. The conversion may take place through mixed-layer formation with increasing illite/smectite ratio at higher temperatures and pressures. This process requires dehydration of the interlamellar space, for which either an external pressure or drying are needed. An alternative mechanism that takes place without dehydration, is dissolution of smectite and neoformation of illite. Both processes imply reorganization of the smectite crystal lattice for which the activation energy is fairly high, meaning that the conversion is negligible at temperatures lower than about 60°C. At elevated temperatures the conversion rate is controlled by the access to potassium for either mechanism.

An ongoing detailed investigation of this subject has led to a tentative model for the smectite-to-illite conversion in natural sediments and in canister-embedding clay in high-level radioactive waste (HLW) repositories.  相似文献   

Limestone deposits and small-scale production of lime in Nigeria     

Samuel A. Ola 《Engineering Geology》1977,11(2):127-137

A general survey of limestone deposits in Nigeria is presented. From these deposits five locations representing the geographical distribution of these deposits were selected and hydrated lime prepared from them. An A-7-6 lateritic soil was stabilized with these locally prepared hydrated limes as well as a commercial lime and the results of unconfined compression, CBR and optimum dry density compared. The results show that the locally prepared limes are not inferior to the commercial limes for soil stabilization and strength characteristics. The results also show that because of the low contents of MgO, the limestones were not sensitive to overheating.  相似文献   

On the turbulent Prandtl number in the stable atmospheric boundary layer     

Andrey A. Grachev  Edgar L Andreas  Christopher W. Fairall  Peter S. Guest  P. Ola G. Persson 《Boundary-Layer Meteorology》2007,125(2):329-341

This study focuses on the behaviour of the turbulent Prandtl number, Pr _t , in the stable atmospheric boundary layer (SBL) based on measurements made during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA). It is found that Pr _t increases with increasing stability if Pr _t is plotted vs. gradient Richardson number, Ri; but at the same time, Pr _t decreases with increasing stability if Pr _t is plotted vs. flux Richardson number, Rf, or vs. ζ = z/L. This paradoxical behaviour of the turbulent Prandtl number in the SBL derives from the fact that plots of Pr _t vs. Ri (as well as vs. Rf and ζ) for individual 1-h observations and conventional bin-averaged values of the individual quantities have built-in correlation (or self-correlation) because of the shared variables. For independent estimates of how Pr _t behaves in very stable stratification, Pr _t is plotted against the bulk Richardson number; such plots have no built-in correlation. These plots based on the SHEBA data show that, on the average, Pr _t decreases with increasing stability and Pr _t < 1 in the very stable case. For specific heights and stabilities, though, the turbulent Prandtl number has more complicated behaviour in the SBL.  相似文献   

A comparison of aeromagnetic levelling techniques with an introduction to median levelling     

Eirik Mauring  Les P. Beard  Ola Kihle  Mark A. Smethurst 《Geophysical Prospecting》2002,50(1):43-54

Aeromagnetic data collected in areas with severe diurnal magnetic variations (auroral zones) are difficult to level. This paper describes levelling of an aeromagnetic survey where such conditions prevail, and where sophisticated levelling techniques are needed. Corrections based on piecewise low‐order polynomial functions are often used to minimize mis‐ties in aeromagnetic data. We review this technique and describe similar mis‐tie fitting methods based on low‐pass filter levelling, tensioned B‐spline levelling and median levelling. It is demonstrated that polynomial levelling, low‐pass filter levelling and tensioned B‐spline levelling depend on the careful editing of outlying mis‐ties to avoid the introduction of false anomalies. These three techniques are equally efficient at removing level errors. Median levelling also removes level errors efficiently, but it is more robust in the sense that mis‐tie editing is not required. This is due to the inherent noise‐removal capabilities of the median filter. After mis‐tie editing, the total field anomalies of the other three techniques closely resemble the unedited median‐levelled total field anomaly.  相似文献   

Calendar time interpolation of amplitude maps from 4D seismic data          下载免费PDF全文

Anders Fredrik Kiær  Ola Eiken  Martin Landrø 《Geophysical Prospecting》2016,64(2):421-430

A calendar time interpolation method for 2D seismic amplitude maps, done in two steps, is presented. The contour interpolation part is formulated as a quadratic programming problem, whereas the amplitude value interpolation is based on a conditional probability formulation. The method is applied on field data from the Sleipner CO₂ storage project. The output is a continuous image (movie) of the CO₂ plume. Besides visualization, the output can be used to better couple 4D seismic to other types of data acquired. The interpolation uncertainty increases with the time gap between consecutive seismic surveys and is estimated by leaving a survey out (blind test). Errors from such tests can be used to identify problems in understanding the flow and possibly improve the interpolation scheme for a given case. Field‐life cost of various acquisition systems and repeat frequencies are linked to the time‐lapse interpolation errors. The error in interpolated amplitudes increased by 3%‐4% per year of interpolation gap for the Sleipner case. Interpolation can never fully replace measurements.  相似文献   

Sedimentological interpretation of coastal ditch cuttings: implications for subsurface geology and provenance in Dahomey Basin,Nigeria     

Peter Sunday Ola  Ekundayo Joseph Adepehin 《Arabian Journal of Geosciences》2017,10(3):65

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A long-term Arctic snow depth record from Abisko, northern Sweden, 1913–2004     

Jack Kohler  Ola Brandt  Margareta Johansson  Terry Callaghan 《Polar research》2006,25(2):91-113

A newly digitized record of snow depth from the Abisko Scientific Research Station in northern Sweden covers the period 1913-present. Mean snow depths were taken from paper records of measurements made on a profile comprising 10 permanent stakes. This long-term record yields snow depths consistent with two other shorter term Abisko records: measurements made at another 10-stake profile (1974-present) and at a single stake (1956-present). The measurement interval is variable, ranging from daily to monthly, and there are no data for about half of the winter months in the period 1930-1956. To fill the gaps, we use a simple snowpack model driven by concurrent temperature and precipitation measurements at Abisko. Model snow depths are similar to observed; differences between the two records are comparable to those between profile and single stake measurements. For both model and observed snow depth records, the most statistically significant trend is in winter mean snow depths, amounting to an increase of about 2 cm or 5 % of the mean per decade over the whole measurement period, and 10% per decade since the 1930-40s, but all seasonal means of snow depth show positive trends on the longest timescales. However, the start, end, and length of the snow season do not show any statistically significant long-term trends. Finally, the relation between the Arctic Oscillation index and Abisko temperature, precipitation and snow depth is positive and highly significant, with the best correlations for winter.  相似文献