The role of vibrationally excited nitrogen and oxygen in the ionosphere over Millstone Hill during 16-23 March, 1990

We present a comparison of the observed behavior of the F region ionosphere over Millstone Hill during the geomagnetically quiet and storm period on 16/23 March, 1990, with numerical model calculations from the time-dependent mathematical model of the Earths ionosphere and plasmasphere. The effects of vibrationally excited N₂(v) and O₂(v) on the electron density and temperature are studied using the N₂(v) and O₂(v) Boltzmann and non-Boltzmann distribution assumptions. The deviations from the Boltzmann distribution for the first five vibrational levels of N₂(v) and O₂(v) were calculated. The present study suggests that these deviations are not significant at vibrational levels v = 1 and 2, and the calculated distributions of N₂(v) and O₂(v) are highly non-Boltzmann at vibrational levels v > 2. The N₂(v) and O₂(v) non-Boltzmann distribution assumption leads to the decrease of the calculated daytime NmF2 up to a factor of 1.44 (maximum value) in comparison with the N₂(v) and O₂(v) Boltzmann distribution assumption. The resulting effects of N₂(v > 0) and O₂(v) > 0) on the NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 2.8 (maximum value) for Boltzmann populations of N₂(v) and O₂(v) and up to a factor of 3.5 (maximum value) for non-Boltzmann populations of N₂(v) and O₂(v). This decrease in electron density results in the increase of the calculated daytime electron temperature up to about 1040/1410 K (maximum value) at the F2 peak altitude giving closer agreement between the measured and modeled electron temperatures. Both the daytime and nighttime densities are not reproduced by the model without N₂(v > 0) and O₂(v > 0), and inclusion of vibrationally excited N2 and O2 brings the model and data into better agreement. The effects of vibrationally excited O2 and N2 on the electron density and temperature are most pronounced during daytime.     

Comparison of the measured and modelled electron densities and temperatures in the ionosphere and plasmasphere during 20/30 January, 1993

We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earths ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20/30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. The deviations from the Boltzmann distribution for the first five vibrational levels of N₂(v) and O₂(v) were calculated. The present study suggests that these deviations are not significant at the first vibrational levels of N₂ and O₂ and the second level of O₂, and the calculated distributions of N₂(v) and O₂(v) are highly non-Boltzmann at vibrational levels v > 2. The resulting effect of N₂(v > 0) and O₂(v > 0) on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 1.5. The modelled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 580 K at the F2 peak altitude giving closer agreement between the measured and modelled electron temperatures. Both the daytime and night-time densities are not reproduced by the model without N₂(v > 0) and O₂(v > 0), and inclusion of vibrationally excited N₂ and O₂ brings the model and data into better agreement.     

Lunar perturbations in geomagnetic field and in the characteristics ofF-region over huancayo

Summary The lunar daily (L) and lunar monthly (M) variations in horizontal magnetic field (H), maximum electron density (N _max ), height of peak ionisation (h _max ), semi-thickness (y _m ) of theF ₂ layer and total electron content (N _t ) at Huancayo for the period January 1960 to December 1961 are described. The lunar tidal variations inh _max follow sympathetically the variations inH such that an increase of magnetic field causes the raising of height of peak ionisation. Lunar tides inN _max are opposite in phase to that ofh _max with a delay of about 1–2 hours, suggesting that an increase of height causes a decrease in maximum electron density. The lunar tides in semi-thickness are very similar in phase to that inh _max . The lunar tidal effects in any of the parameters are largest inD-months and least inJ-months. The amplitude of lunar tides in maximum electron density seems to increase with increasing height whereas the phase seems to be constant with height. It is concluded that lunar tides in the ionospheric parameters at magnetic equator are greatly controlled by the corresponding geomagnetic variations.Presented at the Third International Symposium on Equatorial Aeronomy, Ahmedabad, 3–10 February 1969.     

Comparison of models and data at Millstone Hillduring the 5–11 June 1991 storm

We compare measurements of the ionospheric F region at Millstone Hillduring the severe geomagnetic disturbances of 5–11 June 1991 with results from the IZMIRANand FLIP time-dependent mathematical models of the Earths ionosphere and plasmasphere. Somecomparisons are also made with the Millstone Hill semi-empirical model which was previouslyused to model this storm. New rate coefficients from recent laboratory measurements of the O⁺+N₂ and O⁺+O₂ loss rates are included in theIZMIRAN and Millstone Hill models. The laboratory measurements show that vibrationallyexcited N₂ and O₂ (N₂(v) and O₂(v)) are both important at high temperatures such as found in the thermosphere during disturbedconditions at summer solar maximum. Increases in the O⁺+N₂ loss ratedue to N₂(v) result in a factor ∼2 reduction in the daytime F₂ peak electron density. On some days inclusion of N₂(v) improves theagreement between the models and the data, and on other days it worsens it. In the present workwe show for the first time the significant effect that the increase in the O⁺recombination rate due to O₂(v) may have on the calculated NmF₂. There are considerable uncertainties in the model calculations during the unusual,extremely disturbed conditions found during the daytime on 6 June. The results illustratedifficulties involved and the current state of the art in modelling severe disturbances, and thusprovide a benchmark against which future progress can be gauged.     

New electron energy transfer rates for vibrational excitation of N2

In this paper we present the results of a study of the electron cooling rate, the production rates of vibrationally excited N₂(v), and the production frequency of the N₂ vibrational quanta arising from the collisions of electrons with unexcited N₂(0) and vibrationally excited N₂(1) molecules as functions of the electron temperature. The electron energy transfer rates for vibrational excitation of N₂ have been calculated and fit to analytical expressions by use of the revised vibrationally excited N₂ cross sections. These new analytical expressions are available to the researcher for quick reference and accurate computer modeling with a minimum of calculations.     

Space-Time scales of internal waves

Abstract

We have contrived a model E(αω) α μ^?1ω^?p+1(ω ²?ω _i ²)^?+ for the distribution of internal wave energy in horizontal wavenumber, frequency-space, with wavenumber α extending to some upper limit μ(ω) α ω ^r-1 (ω ²?ω _i ²)^½, and frequency ω extending from the inertial frequency ω _i to the local Väisälä frequency n(y). The spectrum is portrayed as an equivalent continuum to which the modal structure (if it exists) is not vital. We assume horizontal isotropy, E(α, ω) = 2παE(α₁, α₂, ω), with α₁, α₂ designating components of α. Certain moments of E(α₁, α₂, ω) can be derived from observations. (i) Moored (or freely floating) devices measuring horizontal current u(t), vertical displacement η(t),…, yield the frequency spectra F _(u,η,…)(ω) = ∫∫ (U ², Z ²,…)E(α₁, ∞₂, ω) dα₁ dα₂, where U, Z,… are the appropriate wave functions. (ii) Similarly towed measurements give the wavenumber spectrum F _(…)(α1) = ∫∫… dα₂ dω. (iii) Moored measurements horizontally separated by X yield the coherence spectrum R(X, ω) which is related to the horizontal cosine transform ∫∫ E(α1, α2 ω) cos α₁ Xdα₁ dα₁. (iv) Moored measurements vertically separated by Y yield R(Y, ω) and (v) towed measurements vertically separated yield R(Y, α₁), and these are related to similar vertical Fourier transforms. Away from inertial frequencies, our model E(α, ω) α ω ^?p-r for α ≦ μ ω ω ^r, yields F(ω) ∞ ω ^?p, F(α₁) ∞ α₁ ^?q, with q = (p + r ? 1)/r. The observed moored and towed spectra suggest p and q between 5/3 and 2, yielding r between 2/3 and 3/2, inconsistent with a value of r = 2 derived from Webster's measurements of moored vertical coherence. We ascribe Webster's result to the oceanic fine-structure. Our choice (p, q, r) = (2, 2, 1) is then not inconsistent with existing evidence. The spectrum is E(∞, ω) ∞ ω ^?1(ω ²?ω _i ^{2 ?1}, and the α-bandwith μ ∞ (ω ²?ω _i ²)⁺ is equivalent to about 20 modes. Finally, we consider the frequency-of-encounter spectra F([sgrave]) at any towing speed S, approaching F(ω) as S ≦ S _o, and F(α₁) for α₁ = [sgrave]/S as S ≧ S _o, where S _o = 0(1 km/h) is the relevant Doppler velocity scale.     

An anomalous subauroral red arc on 4 August, 1972: comparison of ISIS-2 satellite data with numerical calculations

This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth’s ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the fluxes of precipitating electrons and the additional production rates of N⁺₂, O⁺₂, O⁺(⁴S), O⁺(²D), O⁻(²P), and O⁺(²P) ions, and O(¹D) in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1.05 eV cm⁻³ s⁻¹ was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N₂(v > 0) and O₂(v > 0) in the calculations of the O⁺(⁴S) loss rate improves the agreement between the calculated N_e and the data on 4 August, 1972. The N₂(v > 0) and O₂(v > 0) effects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O⁺ + N₂ rate factor due to the vibrationally excited nitrogen produces the 5–19% reductions in the calculated quiet daytime peak density and the 16–24% decrease in NmF2 in the SAR arc region. The increase in the O⁺ + N₂ loss rate due to vibrationally excited O₂ produces the 7–26% decrease in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O₂(a¹δ_g) and O₂(b¹σ_g⁺), and rotational excitation of O₂, and found that the effect of these cooling rates on T_e can be considered negligible during the quiet and geomagnetic storm period 3–4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O(³P) with thermal electrons with excitation of O(¹D), and the electron cooling rates by vibrational excitation of O₂ and N₂ are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N₂(B³π_g⁺), N₂(C³π_u), and N₂(A³σ_u⁺) at several vibrational levels, O(¹S), and the volume emission rate and integral intensity at 557.7 nm in the region between 120 and 1000 km. We found from the model that the integral integral intensity at 557.7 nm is much less than the integral intensity at 630 nm.     

The role of vibrationally excited oxygen and nitrogen in the ionosphere during the undisturbed and geomagnetic storm period of 6–12 April 1990

We present a comparison of the observed behavior of the F-region ionosphere over Millstone Hill during the geomagnetically quiet and storm periods of 6–12 April 1990 with numerical model calculations from the IZMIRAN time-dependent mathematical model of the Earths ionosphere and plasmasphere. The major enhancement to the IZMIRAN model developed in this study is the use of a new loss rate of O⁺(⁴S) ions as a result of new high-temperature flowing afterglow measurements of the rate coefficients K₁ and K₂ for the reactions of O⁺(⁴S) with N₂ and O₂. The deviations from the Boltzmann distribution for the first five vibrational levels of O₂(v) were calculated, and the present study suggests that these deviations are not significant. It was found that the difference between the non-Boltzmann and Boltzmann distribution assumptions of O₂(v) and the difference between ion and neutral temperature can lead to an increase of up to about 3% or a decrease of up to about 4% of the calculated NmF2 as a result of a respective increase or a decrease in K₂. The IZMIRAN model reproduces major features of the data. We found that the inclusion of vibrationally excited N₂(v > 0) and O₂(v > 0) in the calculations improves the agreement between the calculated NmF2 and the data on 6, 9, and 10 April. However, both the daytime and nighttime densities are reproduced by the IZMIRAN model without the vibrationally excited nitrogen and oxygen on 8 and 11 April better than the IZMIRAN model with N₂(v > 0) and O₂(v > 0). This could be due to possible uncertainties in model neutral temperature and densities, EUV fluxes, rate coefficients, and the flow of ionization between the ionosphere and plasmasphere, and possible horizontal divergence of the flux of ionization above the station. Our calculations show that the increase in the O⁺ + N₂ rate factor due to N₂(v > 0) produces a 5–36% decrease in the calculated daytime peak density. The increase in the O⁺ + O₂ loss rate due to vibrationally excited O₂ produces 8–46% reductions in NmF2. The effects of vibrationally excited O₂ and N₂ on N_e and T_e are most pronounced during the daytime.     

On I(5577 Å) and I (7620 Å) auroral emissions and atomic oxygen densities

A model of auroral electron deposition processes has been developed using Monte Carlo techniques to simulate electron transport and energy loss. The computed differential electron flux and pitch angle were compared with in situ auroral observations to provide a check on the accuracy of the model. As part of the energy loss process, a tally was kept of electronic excitation and ionization of the important atomic and molecular states. The optical emission rates from these excited states were computed and compared with auroral observations of (3914 Å), (5577 Å), (7620 Å) and (N₂VK). In particular, the roles played by energy transfer from N₂(A³⁺_u) and by other processes in the excitation of O(¹S) and O₂(b¹⁺_g) were investigated in detail. It is concluded that the N₂(A³⁺_u) mechanism is dominant for the production of OI(5577 Å) in the peak emission region of normal aurora, although the production efficiency is much smaller than the measured laboratory value; above 150 km electron impact on atomic oxygen is dominant. Atomic oxygen densities in the range of 0.75±0.25 MSIS-86 [O] were derived from the optical comparisons for auroral latitudes in mid-winter for various levels of solar and magnetic activity.     

Earthquake response spectra taking account of number of response cycles

Proposed is a new definition of earthquake response spectra, which takes account of the number of response cycles N. The Nth largest amplitude of absolute acceleration response of a linear oscilator with natural period T and damping ratio h, which is subjected to ground motion at its base, is defined as S_A(T, h, N). By defining a reduction factor η(T, h, N) as S_A(T, h, N)/S_A(T, h, 1), characteristics of η(T, h, N) were investigated based on 394 components of strong motion records obtained in Japan. Two practical empirical formulae to assess the reduction factor η(T, h, N) are proposed.     

Shallow water tidal currents in close proximity to the seafloor and boundary-induced turbulence

Velocity measurements with vertical resolution 0.02 m were conducted in the lowest 0.5 m of the water column using acoustic Doppler current profiler (ADCP) at a test site in the western part of the East China Sea. The friction velocity u _* and the turbulent kinetic energy dissipation rate ε _wl(ζ) profiles were calculated using log-layer fits; ζ is the height above the bottom. During a semidiurnal tidal cycle, u _* was found to vary in the range (1–7) × 10⁻³ m/s. The law-of-the-wall dissipation profiles ε _wl(ζ) were consistent with the dissipation profiles ε _mc(ζ) evaluated using independent microstructure measurements of small-scale shear, except in the presence of westward currents. It was hypothesized that an isolated bathymetric rise (25 m height at a 50-m seafloor) located to the east of the measurement site is responsible for the latter. Calculation of the depth integrated internal tide generating body force in the region showed that the flanks of the rise are hotspots of internal wave energy that may locally produce a significant turbulent zone while emitting tidal and shorter nonlinear internal waves. This distant topographic source of turbulence may enhance the microstructure-based dissipation levels ε _mc(ζ) in the bottom boundary layer (BBL) beyond the dissipation ε _wl(ζ) associated with purely locally generated turbulence by skin currents. Semi-empirical estimates for dissipation at a distance from the bathymetric rise agree well with the BBL values of ε _mc measured 15 km upslope.     

N2 and M2 lunar tides: atmospheric resonance revisited

A numerical model has been used to calculate the atmospheric response to forcing at periods in the region of 12-13.5 h. The results show that the response is enhanced in the neighbourhood of 13 h. These results have been compared with lunar tidal analyses of mesospheric wind data and geomagnetic variations at a number of stations. It is found that the N₂ lunar tidal component (period 12.66 h) is significantly enhanced relative to the main lunar tidal component M₂ (period 12.42 h) in both types of data, compared with what would be expected from the gravitational tidal potential. This supports the predictions of the numerical model. An appreciable phase shift is also found in the experimental data between the N₂ and M₂ tides, agreeing in sense with what would be expected for a resonance at a period around 13 h.     

The relationship between seismic velocity and radioactive heat production in crustal rocks: An exponential law

In crystalline rocks seismic velocityV _p and densityp increase, whereas radioactive heat productionA decreases from acidic to basic compositions. From the velocity-density systematics for crustal rocks at different pressures an empiricalA(V _p) relationship has been derived for the range 5.0–8.0 km/sec which follows the exponential law:A(V _p )=a exp (-bV _p ), where the numerical factorsa andb depend onin situ pressure. A graph is given by means of which the heat production distributionA(z) can be obtained for any givenV _p (z) structure.Contribution No. 207, Institute of Geophysics, ETH Zurich.     

Internal waves in a randomly stratified fluid

Abstract

We discuss the propagation of internal waves in a rotating stratified unbounded fluid with randomly varying stability frequency, N. The first order smoothing approximation is used to derive the dispersion relation for the mean wave field when N is of the form N ² = N _o ²(1 + ?μ), where μ is a centered stationary random function of either depth (z) or time (t), N _o = constant and O < ?² ≦ 1. Expressions are then derived for the change in phase speed and growth rate due to the random fluctuations μ; in particular, attention is focused on the behaviour of these expressions for short and long correlation lengths (case μ = μ(z)) and times (case μ = μ(t)). For the case μ = μ(z), which represents a model for the temperature and salinity fine-structure in the ocean, the appropriate statistics of the fluctuations observed at station P (50°N, 145°W) have been incorporated into the theory to estimate the actual importance of the effects due to these random fluctuations. It is found that the phase speed of the mean wave decreases significantly if (i) the wavelength is short compared to g/N_o ² or (ii) the wave number vector is essentially horizontal and the wave frequency is very close to N _o. Also, the random fluctuations cause a significant growth (decay) in the amplitude of a wave propagating upwards (downwards) through a depth of a few kilometers. However, in the direction of energy propagation, the kinetic energy is conserved. Finally, it is shown that the average effect of the depth dependent fluctuations at station P is to slightly decrease the stability frequency and the magnitude of the group velocity.     

Tidal circulation and energy dissipation in a shallow, sinuous estuary

The tidal dynamics in a pristine, mesotidal (>2 m range), marsh-dominated estuary are examined using moored and moving vessel field observations. Analysis focuses on the structure of the M ₂ tide that accounts for approximately 80% of the observed tidal energy, and indicates a transition in character from a near standing wave on the continental shelf to a more progressive wave within the estuary. A slight maximum in water level (WL) occurs in the estuary 10–20 km from the mouth. M ₂ WL amplitude decreases at 0.015 m/km landward of this point, implying head of tide approximately 75 km from the mouth. In contrast, tidal currents in the main channel 25 km inland are twice those at the estuary mouth. Analysis suggests the tidal character is consistent with a strongly convergent estuarine geometry controlling the tidal response in the estuary. First harmonic (M ₄) current amplitude follows the M ₂ WL distribution, peaking at mid-estuary, whereas M ₄ WL is greatest farther inland. The major axis current amplitude is strongly influenced by local bathymetry and topography. On most bends a momentum core shifts from the inside to outside of the bend moving seaward, similar to that seen in unidirectional river flow but with point bars shifted seaward of the bends. Dissipation rate estimates, based on changes in energy flux, are 0.18–1.65 W m⁻² or 40–175 μW kg^–1. A strong (0.1 m/s), depth-averaged residual flow is produced at the bends, which resembles flow around headlands, forming counter-rotating eddies that meet at the apex of the bends. A large sub-basin in the estuary exhibits remarkably different tidal characteristics and may be resonant at a harmonic of the M ₂ tide.     

小球藻和铜绿微囊藻的高浓度Chl-a高光谱定量模型

本研究将地物高光谱遥感技术应用于室内实验,从而得到小球藻和铜绿微囊藻的高光谱特征.通过多种半经验方法,如单波段、波段比值和微分法,建立了两藻种最优的Chl-a高光谱定量模型,并与室外情况进行了对比.结果表明:小球藻的最优定量模型为Chl-a=174.6 1138292(R703) 2.3(109[(R703)]2(p＜0.01),相应的方法适宜性为:一阶微分法＞单波段法＞波段比值法;铜绿微囊藻的最优定量模型为Chl-a=5299164(R757)1.9773(p＜0.01),相应的方法适宜性为:单波段法＞波段比值法＞一阶微分法;从高光谱特征来看,小球藻在540 nm和700 nm附近存在明显的特征波峰,其位置随Chl-a浓度增大而向长波方向偏离,铜绿微囊藻在530 nm、660 nm和700 nm附近存在3个较强的特征波峰,在610 nm和680 nm附近存在明显的波谷;与以往室外研究不同的是铜绿微囊藻的反射率在400-500 nm之间的R值并不低,是因为没有非藻类颗粒物的影响,总吸收明显降低.     

适用于多种卫星数据的太湖水体漫衰减系数估算算法

下行漫衰减系数(K_d)是描述水下光场的重要参数,决定水体真光层深度,影响着浮游藻类初级生产力及其分布特征.基于2008—2013年太湖4次大规模野外试验数据,分析太湖水体漫衰减系数特征及其影响因素,建立适用于多种卫星数据且较高精度的太湖水体490 nm处下行漫衰减系数估算模型.结果表明:无机悬浮物是太湖水体漫衰减系数的主要影响因素;红绿波段比值(674 nm/555 nm)最适合于太湖K_d(490)估算,模型反演精度较高(N=72,R~2=0.72,RMSE=0.89 m~(-1),MAPE=21.58%);利用实测光谱数据,模拟得到MODIS/EOS、OLCI/Sentinel-3、GOCI/COMS和MSI/Sentinel-2等主要传感器波段的信号,构建适用于多种卫星传感器K_d(490)估算的红绿波段模型,建模精度较高(N=72,R~20.7,RMSE0.9 m~(-1),MAPE22.0%),且进行了验证(N=37,R~20.7,RMSE0.9 m~(-1),MAPE22.0%).     

Effect of stratification on tidal circulation over the Scotian Shelf and Gulf of St. Lawrence: a numerical study using a three-dimensional shelf circulation model

A three-dimensional shelf circulation model is used to examine the effect of seasonal changes in water-column stratification on the tidal circulation over the Scotian Shelf and Gulf of St. Lawrence. The model is driven by tidal forcing specified at the model’s lateral open boundaries in terms of tidal sea surface elevations and depth-averaged currents for five major tidal constituents (M₂, N₂, S₂, K₁, and O₁). Three numerical experiments are conducted to determine the influence of baroclinic pressure gradients and changes in vertical mixing, both associated with stratification, on the seasonal variation of tidal circulation over the study region. The model is initialized with climatological hydrographic fields and integrated for 16 months in each experiment. Model results from the last 12 months are analyzed to determine the dominant semidiurnal and diurnal tidal components, M₂ and K₁. Model results suggest that the seasonal variation in the water-column stratification affects the M₂ tidal circulation most strongly over the shelf break and over the deep waters off the Scotian Shelf (through the development of baroclinic pressure gradients) and along Northumberland Strait in the Gulf of St. Lawrence (through changes in vertical mixing and bottom stress). For the K₁ constituent, the baroclinic pressure gradient and vertical mixing have opposing effects on the tidal circulation over several areas of the study region, while near the bottom, vertical mixing appears to play only a small role in the tidal circulation.     

Determination of thermodynamic properties of (Fe,Mg)-pyroxenes at 1000 K by the emf method

Emf measurements were made on the cell Pt|Fe,(Fe,Mg)_xSi₂O₆,SiO₂|(ZrO₂)_0.85(CaO)_0.15|Fe,FeO|Pt at 1000 K. Using the present data, the standard free energy of formation of ferrosilite (compound FeSiO₃), from the component oxides FeO and SiO₂, is calculated to be −6.35 ± 0.80 kJ/mol. The activity-composition relation for pyroxene solid solution shows that it has a positive deviation from ideality at 1000 K. The present results are compared with the results of other workers.ΔG_mix andΔG^ex are calculated and plotted againstN_FeSiO3.