Growth Rate Spectrum Research Articles

Two-phase liquid phase epitaxy of In0.53Ga0.47As on InP

The growth of the In0.53Ga0.47As epilayer on InP by two‐phase liquid phase epitaxy is investigated. To saturate the In melt before growth, an overweight GaAs wafer is chosen as solid source and put on top of the melt. By adjusting the weight of In, epilayers with a lattice mismatch Δa⊥/a below 2×10−4 are obtained. It is found that the quantity of InAs source required is more than that used in single‐phase growth and the growth rate is smaller in two‐phase growth. The result is explained using the phase diagram and the theoretical calculation. The growth rate, lattice‐mismatch data, and photoluminescence spectra of the epilayers are also presented.

Beam‐density gradient drift instabilities and heating in the plasma sheet boundary layer

The linear and second‐order theories of ion beam‐density gradient drift instabilities on the outer edge of the inhomogeneous plasma sheet boundary layer (PSBL), with warm current sheet ion beams and cold ionospheric ion beams drifting in opposite directions, are examined. It is shown that combined interactions of ion beams and plasma density gradient drifts can excite electrostatic ion beam‐density gradient drift instabilities. These instabilities combine to form the broadband maximum growth rate spectrum with the peak growth rate ∼ 0.34ωlh at the obliquely propagating low frequency, whereωlh is the lower hybrid frequency. These linear results can be used to explain the observed broadband electrostatic noise on the outer edge of the PSBL. The calculations for the second‐order heating rate show that three particle components in the model may be heated by electrostatic waves which result from ion beam‐density gradient drift instabilities. The second‐order heating rates for the cold ionospheric ion beams are the highest. The heating rate profiles with respect to the ambient magnetic field for each component are anisotropic and similar to the maximum growth rate profiles. The peak heating rate occurs at the obliquely propagating low frequency which corresponds to the peak growth rate. The second‐order heating considered here is due to resonance broadening of weak resonant components. These results may be used to understand transport processes on the outer edge of the PSBL.

Numerical Investigations with a Hybrid Isentropic–Sigma Model. Part I: Normal-Mode Characteristics

In a validation experiment of a hybrid isentropic–sigma coordinate primitive equation model developed at the University of Wisconsin (the UW θ−σ model), an initial value technique is used to investigate numerically the normal-mode characteristics of baroclinically amplifying disturbances over a spectrum of meteorologically significant wavelength. The experiments are designed to determine the impact of coupling an isentropic-coordinate free atmospheric domain to a sigma-coordinate planetary boundary layer (PBL) on the normal-mode characteristics. The growth rate and phase speed spectra of the most unstable normal modes are obtained for an analytically prescribed zonal flow field. The evolution and vertical structure of the kinetic energy, energy conversions, growth rates, and geopotential fields are investigated. Several modifications have been made to earlier versions of the UW θ−σ model to overcome noise introduced by adjustments associated with emerging and submerging grid volumes at the sigma–isentropic interface. With these modifications, the hybrid model accurately simulates the evolution and structure of normal-mode baroclinic disturbances for all wavenumbers considered except for wavenumber two. The normal-mode growth rate and phase speed spectra compare well with previous studies using standard sigma coordinate models. There is no evidence of aliasing the baroclinic normal-mode characteristics due to the coupling of isentropic and sigma domains.

Nonlocal theory of long‐wavelength plasma waves associated with sporadic E layers

In this paper we calculate the nonlocal growth rate of gradient drift plasma waves under conditions where the electron density gradient scale length changes with altitude. The results are compared with the local growth rate and discussed in the context of the kilometer‐scale waves which have been observed in the vicinity of mid‐latitude sporadic E layers. These large‐scale waves drastically violate the local approximation, kLm»1, where k is the irregularity wave number and Lm is the minimum gradient scale length on the edge of a layer. The first step in the analysis is to derive a general eigenmode equation, starting with the same assumptions usually used in the derivation of the local dispersion relation for long wavelength waves. Modeling a sporadic E layer as a slab, the nonlocal growth rate spectrum is found by solving the eigenmode equation for this profile. The solution is an algebraic dispersion relation with a growth rate spectrum which is roughly proportional to k, rather than the k2 dependence predicted by conventional local theory at long wavelengths. At short wavelengths the nonlocal growth rate determined with the slab is unbounded, in disagreement with local theory. The slab is an inadequate model for short wavelength waves and a bound on the growth rate is instead derived from a theory which can be applied to any realistic profile with nonzero Lm. At short wavelengths this bound is identical to the local growth rate expression, while at long wavelengths the bound remains proportional to k and thus is consistent with the dispersion relation for a slab. Nonlocal effects alone do not explain the dominance of kilometer scales, but they do tend to favor the excitation of long wavelengths.

Baroclinic Instability at Short Wavelengths in Vertically Discrete Quasi-Geostrophic and Ageostrophic Models

Short wavelength linear baroclinic instability is examined numerically in two quasi-geostrophic models and one ageostrophic model. The growth rate spectra for the ageostrophic model differ little from those of the quasi-geostrophic models in three cases with different arrangements of shear and static stability. In all models and cases, and for 26 vertical levels, peaks of instability were found at very short wavelengths of a few hundred kilometers. These apparently represent spurious critical layer instability appearing at discrete levels, as suggested by Arakawa. They disappear when very high vertical resolution (e.g., 150 levels) is used.

Virulence and Enzyme Production of Erwinia carotovora ssp. atroseptica on Potato Tuber Tissue

AbstractThe elicitation of pathogenesis on potato tuber slices by 6 strains of Erwinia carotovora ssp. atroseptica was investigated by neutral red vital staining and has been compared with bacterial growth rate, penetration ability, enzyme production and enzyme spectrum. The induction of enzyme synthesis (particularly, of the extracellular polygalacturonase) elicites the rot attack on tuber tissue and this requires a sufficient bacterial density.Due to wound healing, the inductors of enzyme production are removed, and after 48 h enzymes do not attack tuber tissue any more. Therefore, growth rate and penetration ability (to get the necessary bacterial density and inductor substances) may limit virulence. A similar influence of enzyme production and enzyme spectrum of the strains on the virulence was not detected.

A Combined Barotropic-Baroclinic Instability Study of the Upper Tropospheric Tropical Easterly Jet

A combined barotropic-baroclinic stability analysis is performed for an upper tropospheric tropical easterly jet representing the observed mean monsoon zonal flow during summer. Numerical solutions are obtained by time integration of a 20-layer linear spectral quasi-geostrophic model, which is based on truncated Fourier series representations in y. It is seen from the growth rate and phase speed spectra that the asymmetric barotropic-baroclinic preferred wave has a wavelength of 6500 km, an e-folding time of 3.3 days, a westward phase speed of 20.5 m s− and a period of 3.8 days. The geopotential, vertical velocity and temperature fields associated with the most unstable barotropic-baroclinic wave are computed. The most unstable wave has a vertical scale of 125 mb, a meridional scale of 1650 km and a zonal scale of 2135 km. The relationship between the vertical and meridional scales of the wave with the corresponding basic zonal flow scales is discussed. The large southward easterly momentum transports associated with the unstable wave are essentially due to the antisymmetric components of the jet. The computed sensible heat transports are found to be down the basic state meridional temperature gradient. The energetics of the unstable wave is computed and it is inferred that the energy sources for the wave growth lie in a narrow vertical layer around the jet level. It is also found that the contribution of baroclinic process is larger than the contribution of barotropic in the wave growth. The contribution of different processes in the movement of the unstable wave are also investigated. The beta effect is identified as the most important physical factor responsible for the westward propagation of the wave.

Ballooning mode spectrum in general toroidal systems

A WKB formalism for constructing normal modes of short-wavelength ideal hydromagnetic, pressure-driven instabilities (ballooning modes) in general toroidal magnetic containment devices with sheared magnetic fields is developed. No incompressibility approximation is made. A dispersion relation is obtained from the eigenvalues of a fourth-order system of ordinary differential equations to be solved by integrating along a line of force. Higher-order calculations are performed to find the amplitude equation and the phase change at a caustic. These conform to typical WKB results. In axisymmetric systems, the ray equations are integrable, and semiclassical quantization leads to a growth rate spectrum consisting of an infinity of discrete eigenvalues, bounded above by an accumulation point. However, each eigenvalue is infinitely degenerate. In the nonaxisymmetric case, the rays are unbounded in a four-dimensional phase space, and semiclassical quantization breaks down, leading to broadening of the discrete eigenvalues and the accumulation point of the axisymmetric unstable spectrum into continuum bands. Analysis of a model problem indicates that the broadening of the discrete eigenvalues is numerically very small, the dominant effect being broadening of the accumulation point.

Contribution of baroclinic mechanism in the formation of the depression during MONEX-79

A linear baroclinic stability analysis is performed for the basic vertical zonal wind profile prior to the formation of the depression during Bay of Bengal phase of MONEX-79 by utilizing a quasi- geostrophic, multilayer, numerical model. The preferred wavelength obtained from the growth rate spectrum is 1400 km for the channel width 1500 km, with an e-folding time 5.2 days. The wave structure in the vertical is computed and compared with the observed structure of the depression. Many common features are noticed between them. Further, the vertical structure of the preferred wave obtained from the modified wind profile, removing wind shear below the westerly maximum level, shows closer agreement to the depression structure than that obtained from the full profile. The effect of vertical variation of static stability in the lower layers on the growth of short unstable waves is studied. It is found that a decrease in static stability in the lower layers resulted in the increase in growth rate and decrease in the preferred wavelength.

Relativistic generalization of whistler mode modulational instability

The modulational instability of whistler mode waves interacting with relativistic plasma has been studied. The application of the Karpman and Krushkal criterion to the nonlinear Schrödinger wave equation gives the spectrum of modulationally unstable whistler mode waves. The effect of relativistic particles on the growth rate and frequency spectrum of modulationally unstable whistler mode waves has been discussed.

The effect of turbulence on the K-parallel-B relativistic beam instability

We have considered the effect of magnetic turbulence, causing electron gyrophase diffusion, on the instability of an anisotropic, field-aligned relativistic electron beam. Formally, inclusion of gyrophase diffusion results in a change in the formula for the wave growth rate whereby the delta function describing the wave-particle resonance is replaced by a Lorentzian function. The width of the Lorentzian, delta, is directly proportional to the strength of the gyrophase diffusion coefficient. Depending on the properties of the beam and the background plamsa, the magnetic irregularities may either enhance or diminish the growth rate, or even produce a transition from wave growth to wave damping. Two of the more interesting results to emerge from our analysis are: (1) contrary to conventional opinion, some types of electron beams may exist without being isotropized by self-generated Alfven waves, (2) due to the frequency dependence of the broadening parameter delta, the actual growth rate spectrum might differ substantially from that calculated for a homogeneous plasma, even though the perturbations are still in the linear regime.

Modulational instability in a plasma with suprathermal electrons

The consequences of the presence of suprathermal electrons on the linear stage of modulational instabilities are investigated for a range of parameters appropriate to both laboratory and astrophysical plasmas. Substantial modifications to the growth rate and secondary spectrum are found to occur for instabilities driven by large amplitude Langmuir waves in the dipole limit due to the kinetic effects of the suprathermal electrons. In particular, for reasonable choices of pump amplitude and suprathermal energy density, additional modes become unstable.

Inorganic Carbon Limitation and Chemical Composition of Two Freshwater Green Microalgae

Two freshwater chlorophytes, Chlorella vulgaris and Scenedesmus obliquus, were grown in inorganic carbon-limited continuous cultures in which HCO(3) was the sole source of inorganic carbon. The response of the steady-state growth rate to the external total inorganic carbon concentration was reasonably well described by the Monod equation; however, the response to the internal nutrient concentration was only moderately well represented by the Droop equation when the internal carbon concentration was defined on a cellular basis. The Droop equation was totally inapplicable when total biomass (dry weight) was used to define internal carbon because the ratio of carbon to dry weight did not vary over the entire growth rate spectrum. In batch cultures, maximum growth rates were achieved at the CO(2) levels present in atmospheric air and at HCO(3) concentrations of 3 mM. No growth was observed at 100% CO(2). Both nitrogen uptake and chlorophyll synthesis were tightly coupled to carbon assimilation, as indicated by the constant C/N and C/chlorophyll ratios found at all growth rates. The main influence of inorganic carbon limitation appears to be not on the chemical structure of the biomass, but rather on cell size; higher steady-state growth rates lead to bigger cells.

Novel effects of magnetic field on the silane glow discharge

We have measured the optical-emission spectra of the silane plasma as a function of the external magnetic field, together with the growth rate and vibrational spectra of the resulting a-Si:H films. The optical-emission intensities of the reactive species SiH, H2, and H produced in the plasma are appreciably affected by the magnetic field, and the corresponding change in the hydrogen bonding of the deposited films is interpreted in terms of chemical reaction among the species.

A Comparison of Baroclinic Instability with the Time Variations of Kinetic Energy in a General Circulation Model

Abstract The flow generated by a general circulation model is zonally averaged at 1-day intervals, and, for each of the axisymmetric flows obtained, the linear growth-rate spectrum for baroclinic waves is computed using a linear model. The time sequence of these linear growth-rate spectra is compared to the corresponding time sequence of kinetic-energy spectra for the flow of the general circulation model, in order to-test the hypothesis that the baroclinic instability of the axisymmetric flow is an important factor in determining variations of the amplitudes of the midlatitude eddies. No significant correlation is found between the linear growth rate of a particular wavenumber and the kinetic energy of that wave at some later time.

Role of Baroclinic Instability in the Development of Monsoon Disturbances

A linear baroclinic stability analysis of the zonal wind representing the mean monsoon situation over India is performed by the use of a multi-level quasi-geostrophic numerical model. An initial value approach is chosen to determine the instability characteristics of the wind. The dependency of the growth rate spectrum on the number of levels in the vertical and on the presence of vertical walls is studied. It is shown that 20 levels in the vertical are sufficient to realize the baroclinic instability of the monsoon mean wind. A shorter unstable wave of wavelength 1500 km and a longer unstable wave of wavelength 4750 km are found to be the most preferred growing waves from the growth rate spectrum. The shorter unstable wave is essentially confined below 500 mb, whereas the longer unstable wave is above 500 mb. It is also shown that the removal of wind shear below (above) the level of the westerly (easterly) jet from the wind profile, shifts the shorter (longer) unstable wave toward higher wavelengths by ∼ 1000 km, with a significant decrease in the growth rates. The horizontal scale (1500 km), level of nondivergence (900 mb), and level of maximum intensity (825 mb) associated with the shorter unstable wave are in close agreement with the observed values, obtained from a composite monsoon depression. The computed phase velocity of the unstable wave is opposite to the observed westward motion. The computed levels of cold core, warm core and top of the wave are at 900, 800 and 500 mb, respectively, which are ∼100 mb lower than the observed levels. The computed phase velocity of the longer unstable wave (−23 m s−1) is found to be very close to the observed value for disturbances along the easterly jet level. The longer unstable wave has a level of nondivergence at 200 mb which is supported from the results of barotropic studies obtained by others.

A comparison of intense electrostatic waves near fUHR with linear instability theory

Intense electrostatic waves beyond the plasmapause have recently been identified at frequencies near the upper hybrid resonance frequency. In addition, the waves occur within a band at an odd, half‐harmonic of the local electron gyrofrequency. These bands of electrostatic turbulence are among the most intense waves detected within the earth’s magnetosphere. Measurements obtained with the ISEE 1 plasma wave receiver show that the intense waves appear to be intensifications of an electrostatic cyclotron harmonic band near the upper hybrid resonance frequency. A straightforward explanation of intense waves at the upper hybrid resonance frequency exists in the electrostatic multi‐cyclotron emission theory. For a broad range of plasma parameters nonconvective instability or large spatial growth rates occur within the cyclotron band encompassing the cold upper hybrid frequency. Comparison of spatial growth rate spectra with measured wave spectra shows that there is excellent qualitative agreement between the linear theory and the observed wave characteristics.

Baroclinic Instability and the Selection of the Zonal Scale of the Transient Eddies of Middle Latitudes

Abstract Because the linear growth rates of baroclinic waves on realistic zonal flows are largest at relatively high zonal wavenumbers (e.g., 15), the observed peaks in the transient kinetic energy spectrum cannot be explained simply by peaks in the linear growth-rate spectrum. When the growth-rate spectrum is fairly flat, as suggested by recent studies, then as the waves evolve, the decrease of the instability of the zonal flow and the increase of dissipation in the developing waves become important in determining which wavelength will dominate after the waves are fully developed. In particular, the stabilization of the zonal flow because of northward and upward eddy transport (which is primarily confined to the lower troposphere in all baroclinic waves) causes the instability of the short baroclinic waves (wavenumber > 10) to decrease more rapidly than that of the intermediate-scale waves (wavenumber <10). In addition, as it is usually modeled, dissipation increases with time more rapidly in the short w...

The Effect of the Meridional Circulation on the Baroclinic Instability of the Winter Zonal Flow

Abstract The linear instability of the observed winter zonal mean flow, with and without the inclusion of the meridional circulation, is presented. The purpose of this note is to determine whether the meridional circulation has an important effect on the growth-rate spectrum and structure of the linear baroclinic waves. It is found that the inclusion of the meridional circulation produced only slight changes in the growth-rate spectrum, as compared to the case where the meridional flow is neglected. The presence of the meridional flow destabilized all wavenumbers greater than 5, although the change was less than 7% for all wavenumbers. The maximum growth rate, with or without considering meridional circulation, occurred between wavenumbers 12 and 15. The wave structures were also very similar in the two cases. The maximum amplitude of the geopotential perturbation for wavenumbers 5–7 remains at the earth’s surface when the meridional circulation is included; however, the position of the maximum geopotenti...

Growth Rates and Phase Speeds of Baroclinic Waves in Multi-Level Models on a Sphere

Abstract The complete growth rate and phase spectra of unstable baroclinic disturbances are studied in multi-level quasi-geostrophic spherical models and in a two-level non-geostrophic model, for two basic zonal jet-profile flows. The eigenvalue method employed has the advantages over initial value approaches of determining all the disturbance modes, being more efficient computationally and avoiding problems of slow convergence or lack of convergence when there are two modes of similar growth rates. The method is used to re-examine the spectra for Simmons and Hoskins' 30° jet and Gall's 42.1° jet. It is found that the disrepancies between our two-level and multi-level results are not as great as found by Simmons and Hoskins using primitive equation models, particularly with respect to phase speeds and momentum fluxes. Further, the short-wave maximum at zonal wavenumber 16 in their five-level primitive equation model does not occur here. Instead, our growth rates for the fastest growing modes are very simi...