Cold Temperature Anomalies Research Articles

Interannual variability of oceanic CO2 and biogeochemical properties in the Western North Atlantic subtropical gyre

Understanding the relationship between Earth's climate and the oceanic carbon cycle requires an understanding of the time-variations of CO2 in the ocean, it's exchange with the atmosphere, and the rate of uptake of anthropogenic CO2 by the ocean. Since 1988, hydrographic and biogeochemical data have been collected at the Bermuda Atlantic Time-Series Study (BATS) site in the Sargasso Sea, located in the North Atlantic subtropical gyre. With over a decade of oceanographic data, interannual trends of CO2 species and air–sea exchange of CO2 at BATS can be examined. Between 1988 and 1998, surface seawater total carbon dioxide (TCO2) and salinity normalized TCO2 (nTCO2) increased at a rate of 2.2±6.9 and 1.6±5.8 μmol kg−1 yr−1, respectively. During the same period, the partial pressure of CO2 (pCO2) of seawater increased at a rate of 1.4±10.7 μatm yr−1, similar to the rate of increase in atmospheric pCO2 (∼1.3 μatm yr−1). The increase in seawater TCO2 and pCO2 can be attributed to a combination of uptake of anthropogenic CO2 from the atmosphere and interannual changes in hydrographic properties of the subtropical gyre. Underlying interannual trends were examined by determining how hydrographic and biogeochemical anomalies, or deviations from the mean state, vary over time. Significant correlations existed between anomalies of temperature, salinity, integrated primary production, mixed-layer depth, TCO2, salinity normalized TCO2 (nTCO2), and alkalinity. For example, cold temperature anomalies (up to −0.5°C) in 1992 and 1995 were associated with increased mixed-layer depth, higher rates of integrated primary production (<∼100 mg C m2 d−1), and higher concentrations of nTCO2 (<∼5 μmol kg−1). The interannual anomalies of hydrography and ocean biogeochemistry were partially linked to large-scale climate variability such as North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO). Temperature, mixed-layer depth, primary production and TCO2 anomalies were correlated with NAO variability, with cold anomalies at BATS generally coinciding with NAO negative states. Salinity, alkalinity and nTCO2 anomalies were correlated with the Southern oscillation index (SOI), lagging ENSO events by 6–12 months.

Covariation of mesoscale ocean color and sea-surface temperature patterns in the Sargasso Sea

During the lifetime of the Coastal Zone Color Scanner, there were 21 instances in which both satellite-derived ocean color and sea-surface temperature are simultaneously available over large areas of the Sargasso Sea. These images reveal close correspondence between mesoscale structures observed in temperature and pigment fields. In general, higher (lower) pigment biomass occurs in mesoscale features consisting of cold (warm) temperature anomalies. This relationship is consistent with the idea that upward displacement of isopycnals at the base of the euphotic zone by mesoscale eddies is an important mechanism of nutrient supply in the region.

A Study of Temperature Changes in the Upper North Atlantic: 1950–94

In this paper, decadal evolution of warm and cold anomalies in the subtropical and subpolar gyres of the North Atlantic in the 300‐500-m and 100‐250-m depth ranges is described. A series of pentadally averaged objective maps of upper-ocean thermal anomalies, from bathythermograph data, are presented. Warm and cold anomalies in the western subtropical gyre are succeeded by similar anomalies in the subpolar gyre and the east Atlantic and subtropical return flow. Major warm and cold anomalies in the 1950s and 1970s, respectively, are similar to those described previously in SSTs, although there is more temporal continuity in the subsurface anomalies. Two very strong events in the subtropical gyre are identified, a cold anomaly in 1966‐72 and an intense warm anomaly in 1988‐94, that show the greatest temperature anomalies in the North Atlantic during the period of the study. Interisotherm thickness anomalies are shown for the subtropical gyre during these periods. In the warm period, mode waters are both warmer (188‐198C) and of greater volume than on average, and lie in a narrow band south of the Gulf Stream above a depressed thermocline with warm temperature anomalies to at least 800-m depth. In the cold period, the predominant mode water temperature is closer to 178C, but there is reduced water formation overall with a raised thermocline and cold temperature anomalies down to 600-m depth. The bowl of the gyre is flat during the cold period, and the implied recirculation may be weaker and extend farther to the south. The changes appear to be consistent with the intensification of the subtropical gyre in the warm period and a spindown in the cold period, although the relative roles of wind stress and air‐sea heat fluxes in these changes need to be determined.

Molecular Dynamics(MD) simulation of the elasticity of MgSiO3 perovskite and the temperature anomaly in the lower mantle.

We performed the molecular dynamics simulation of the elastic properties of MgSiO3 perovskite under the lower mantle conditions to estimate the temperature anomalies in the Earth's interior. The simulated P and S wave velocity anomalies corresponding to the temperature anomaly of 500 K are ±1.11% and ±1.13% respectively at the top of the layer, and are ±0.75% and ±0.78% respectively at the core-mantle boundary. Seismologically observed ratios of the P and S wave velocity anomalies R (=∂lnVs/∂lnVp), due to temperature difference are consistent with the simulated R values, after an anelastic correction, of MgSiO3 perovskite or pyrolite (a mixture of MgO and MgSiO3 perovskite). Both P and S wave velocity anomalies at the top of the lower mantle correspond to the cold temperature anomalies of 120 K for the cold slabs in which MgSiO3 perovskite is dominant. The magnitude of the P wave velocity anomaly observed, after the anelastic correction, at the core-mantle boundary corresponds to about +270 K. The large S wave velocity anomalies at the core-mantle boundary may be accounted for partial melting and/or the chemical heterogeneity due to relatively high iron contents and the temperature anomaly in this region.

Decadal Variabilities of the Upper Layers of the Subtropical North Atlantic: An Ocean Model Study

Numerical simulations of the Atlantic Ocean during the period 1950 to 1989, using a sigma coordinate, free surface numerical model, show long-term variabilities in the upper ocean subtropical gyre similar to those obtained from observations. The simulations show how westward propagating planetary waves, originated in the eastern North Atlantic, affect interdecadal variabilities of ocean properties such as the Bermuda sea level, the Gulf Stream position and strength, and subsurface temperature anomalies in the western North Atlantic. Special attention is given to the dramatic sea level drop at Bermuda in the early 1970s, which is accompanied by cooling of subsurface layers in the western North Atlantic and a northward shift and weakening of the Gulf Stream. Following these events, between 1970 and 1980, the cold temperature anomalies in the upper layers of the western North Atlantic slowly propagated eastward and downward; the strongest propagating signal in the model is found at 200-m depth, suggesting that advection of anomalies downstream by the Gulf Stream current and changes in winter mixing are involved. Significant correlations were found between the sea level anomalies at Bermuda and sea level anomalies in the eastern North Atlantic up to eight years earlier. Sensitivity experiments with different atmospheric forcing fields are used to study the ocean response to observed sea surface temperature and wind stress anomalies. It is shown that on decadal timescales, the ocean model responds in a linear fashion to the combined effect of SST and wind stress anomalies, a fact that might be exploited in future climate prediction studies.

Characteristics and vertical distribution of Atlantic cod (&lt;I&gt;Gadus morhua&lt;/I&gt;) eggs in the northern Gulf of St. Lawrence, and the possible effect of cold water temperature on recruitment

In early May from 1993 to 1995 the water column in the northern Gulf of St. Lawrence was weakly stratified, with cold water (<2°C) extending from ca. 125 m to the surface. Cod (Gadus morhua) eggs were distributed throughout the water column, but higher densities were observed in the cold intermediate layer. The vertical distribution of cod eggs was determined by egg size and organic (lipids, proteins) composition. Stage I egg density estimates in May 1994 ranged from 25.0 to 26.0 kg · m-3, which is higher than the water density of the upper mixed layer. Between 1980 and 1989, there was a weak positive relationship between the cold intermediate layer temperature anomalies and cod year-class strength (i.e., abundance of 3-year-old cod). However, it is unlikely that low recruitment levels caused by below-average temperature of the cold intermediate layer alone had a major impact on the recent collapse of the northern Gulf stock. Nevertheless, the poor state of the spawning stock (low abundance, poor fish condition, and less buoyant eggs) and harsh late winter and early spring conditions in the northern Gulf can limit the potential for high recruitment and rapid recovery of the northern Gulf cod stock.

Characteristics and vertical distribution of Atlantic cod (Gadus morhua) eggs in the northern Gulf of St. Lawrence, and the possible effect of cold water temperature on recruitment

In early May from 1993 to 1995 the water column in the northern Gulf of St. Lawrence was weakly stratified, with cold water (&lt;2°C) extending from ca. 125 m to the surface. Cod (Gadus morhua) eggs were distributed throughout the water column, but higher densities were observed in the cold intermediate layer. The vertical distribution of cod eggs was determined by egg size and organic (lipids, proteins) composition. Stage I egg density estimates in May 1994 ranged from 25.0 to 26.0 kg · m-3, which is higher than the water density of the upper mixed layer. Between 1980 and 1989, there was a weak positive relationship between the cold intermediate layer temperature anomalies and cod year-class strength (i.e., abundance of 3-year-old cod). However, it is unlikely that low recruitment levels caused by below-average temperature of the cold intermediate layer alone had a major impact on the recent collapse of the northern Gulf stock. Nevertheless, the poor state of the spawning stock (low abundance, poor fish condition, and less buoyant eggs) and harsh late winter and early spring conditions in the northern Gulf can limit the potential for high recruitment and rapid recovery of the northern Gulf cod stock.

Dynamical Adjustment of Mesoscale Convective Anvils

Abstract Observational evidence indicates that upper-tropospheric and lower-stratospheric anticyclones occur in mesoscale convective systems, possibly resulting from the vertical redistribution of mass. The authors examine the gradient adjustment process that occurs when mass from the lower troposphere is impulsively injected between isentropic levels in the vicinity of the tropopause. Formulating the quasi-static primitive equations for inviscid, adiabatic, axisymmetric flow on an f plane using entropy and potential radius coordinates allows us to compute the final state in gradient balance by solving a single nonlinear elliptic problem. Solutions of this elliptic problem illustrate the development of an anticyclonic lens at the level of mass injection, with accompanying cold and warm temperature anomalies above and below, respectively. For a given amount of injected mass, a lower-stratospheric injection results in a stronger anticyclone than does an upper-tropospheric injection. Mass injections at low l...

The response of an ocean general circulation model to long time‐scale surface temperature anomalies

Abstract A series of experiments are performed to examine the response of an ocean general circulation model to different surface temperature anomalies. The model used is the Bryan‐Cox primitive equation model, with a horizontal resolution of 2° × 2° in longitude/latitude and an idealized North Atlantic basin geometry. Ten levels are used in the vertical. The model is forced at the surface by temperature anomalies with magnitudes characteristic of simulated global warmings. The time‐scales of the forcing consist of an abrupt switch‐on, as well as a gradual switch‐on forcing over 100 years. The sensitivity to lateral and isopycnal mixing, and the asymmetry of the responses to warm and cold temperature anomalies are also examined. There is an asymmetric behaviour in the transient response for the warm and cold anomaly cases, with the cold case responding more energetically. However, the new equilibrium circulations are approximately symmetric. The warm anomaly case forces a weakened ther‐mohaline circulation in the short term and a strengthened thermohaline circulation in the long term. The opposite behaviour is observed for the cold anomaly case. The abrupt and gradual time‐scales of the forcing produce identical equilibrium circulations but different transient responses. The isopycnal mixing parametrization yields a more rapid and energetic response compared to lateral mixing.

Tropopause Undulations and the Development of Extratropical Cyclones. Part I. Overview and Observations from a Cyclone Event

Abstract The hypothesis that the development of extratropical cyclones is influenced by the evolution of tropopause undulations is described and examined. These undulations exhibit large temperature and potential vorticity anomalies, and are often observed prior to and during surface cyclogenesis. Typically, an undulation has a half wavelength of approximately 2000 km and a vertical amplitude of over 200 mb. Warm and cold temperature anomalies which lie respectively over the low and under the high portions of the undulation, are often embedded within strong upper-level flow, so that large temperature advections are found upstream and over developing cyclones. A case analysis of a cyclone event indicates that the distributions of tropospheric height change and vorticity change can be strongly sensitive to the undulation-related temperature changes in the lower stratosphere, especially near 200 mb.

インドにおける夏のモンスーンの変動に関する解析

Temporal fluctuations appearing in the summer monsoon over India are investigated by using the data of 1962. By the method of spectrum analysis, it is revealed that two major periodicities exist, at least, in the temporal fluctuation of the monsoon. One is the oscillation around 5 days period and the other is around 15 days pericd.The oscillation around 5 days period appears mainly in the range from the north Bay of Bengal through the monsoon trough region in northern India. The structure of the disturbance which causes this periodicity is examined by the method of cross spectrum analysis. The results show that the disturbance is a westward-moving one and its longitudinal wavelength is about 30°. This disturbance seems to represent the so-called monsoon low. The vertical structure of these monsoon lows indicates that their cyclonic circulation is prevailing in the lower troposphere and the axis of the trough slightly tilts westward. Moreover, the monsoon low is accompanied with a distinct warm core in the upper troposphere. In the lower levels, the amplitude of the temperature is mall and the disturbance is neither warmnor cold cored. It is also shown that the monsoon low has a steering level at the height around 500mb level.The oscillation around 15 days period is revealed to be in connection with the active/weak cycle of monsoon. The intense wind fluctuations associated with this cycle appear both in the upper and the lower troposphere, being in phase with each other. At the stage of active monsoon, it is revealed that the area with cyclonic circulation is formed over the Bay of Bengal. This cyclonic circulation is accompanied with cold temperature anomalies in the lower troposphere and warm anomalies in the upper levels. Besides, it is also shown that the depth of the moist layer over the Bay increases at this stage. These situations strongly suggest that the active monsoon condition over India is characterized by the enhanced convective activity over the Bay. Nearly opposite situations occur at the stage of weak monsoon and the anticyclonic circulation is formed over the Bay. The latitudinal shift of monsoon trough can be explained by superposing these two circulations on the distribution of the mean flow.The transition between the active and the weak stage is also investigated by applying the time-composite technique to the time series of surface pressure anomalies. At the stage of active monsoon, a large low pressure area is formed over the Bay of Bengal and the high pressure anomalies appear at the weak stage. By examining the time sequences of this transition, it is shown that a pair of high- and low pressure anomalies rotate clockwise over the wide area including the Bay of Bengal, Tibetan Plateau, whole Indian subcontinent and Indo-China. As for the nature of this rotation, it is suggested that the north-south standing oscillation between Tibetan Plateau and the Bay of Bengal together with the east-west one between Indo-China and the Indian continent can cause the clockwise rotation mentioned above. It is also discussed that these oscillations seem of reflect the temporal variations of the intensity of the mean meridional- and the mean zonal circulation cells respectively.