The nonlinear evolution of the electrostatic Kelvin-Helmholtz instability, resulting from velocitysheared plasma flows perpendicular to an ambient magnetic field, has been studied including Pedersen conductivity effects (i.e., ion-neutral collisions). We find that the Kelvin-Helmholtz instability develops in a distinctly different manner in the nonlinear regime with Pedersen coupling than without it. Specifically, we show that Pedersen coupling effects, in conjunction with a neutral wind and density gradient, (1) result in an increased time scale for Kelvin-Helmholtz instability wave growth, (2) inhibit Kelvin-Helmholtz vortex formation, (3) lead to nonlinear structures which can be described as "breaking waves," and (4) generate, in the nonlinear regime, small scale turbulence by means of secondary instabilities growing on the primary waves. We have also computed the spatial power spectra of the electrostatic potential and density fluctuations and find that there is a tendency for the potential and density spectra to become shallower when Pedersen conductivity effects are included. We compare our results with recent Dynamics Explorer satellite observations of velocity-sheared plasma flows in the high-latitude, near-Earth space plasma and find good agreement. Recently, much experimental [Basu et al., 1988; Weber and Buchau, 1981; Bythrow et al., 1984; Cerisier et al., 1985; Rodriquez and Szuszczewicz, 1984; Curtis et al., 1982; Baker et al., 1986; Vickrey et al., 1980] and theoretical (for recent reviews, see Keskinen and Ossakow [1983] and Kintner and $eyler [1985] and references therein) attention has been given to the origin of high-latitude ionospheric and magnetospheric plasma turbulence. The Kelvin-Helmholtz or velocity-shear driven instability can lead to both electric field and density fluctuations in the high-latitude near-Earth space plasma [see, for example, Kintner and Seyler, 1985]. Studies of velocitysheared flows in space plasmas can be divided into two groups depending upon whether plasma flow velocities are either parallel [Paper number 7A9077. 0148-0227/88/007A-9077505.00 Mishin, 1981; Lee et al., 1981; Walker, 1981; Keskinen and Huba, 1983] or perpendicular [Hallinan and Davis, 1970; Miura and Sato, 1978; Miura and Pritchett, 1982; Pritchett and Coroniti, 1984; Thompson, 1983] to the ambient magnetic field. Both cases have been studied in the MHD [Mikhailovskii, 1974; Sen, 1964; Southwood, 1968] and electrostatic [D'An•lelo, 1965; Smith and yon Goeler, 1968] limits. Furthermore, the velocity, in both cases, is usually taken to vary spatially transverse to the magnetic field in the electrostatic limit. In this study we restrict ourselves to sheared flows perpendicular to the geomagnetic field. Hallinan and Davis [1970] and Webster and Hallinan [1973] have attributed the small scale vortex configurations often seen near auroral arcs [Hallinan and Davis, 1970; Oquti, 1974] to be driven by a transverse Kelvin-Helmholtz or velocity shear driven instability. Kintner [1976] and Kelley and Carlson [197...

[1] Effective estimates of the magnitude and frequency of precipitation are necessary for hydrological designs. However, often the available data at target site are inadequate to arrive at reliable estimates. Practicing hydrometeorologists overcome this impediment by pooling information at target site with that from other locations depicting similar characteristics of precipitation. To facilitate pooling of information, hydrometeorologists use regionalization approaches for partitioning sites in the study region into groups having similar precipitation characteristics. The conventional approaches to regionalization are based on statistics computed from observed precipitation, rather than attributes affecting hydrometeorology in a region. Therefore independent validation of the delineated regions for homogeneity in precipitation was not possible. To address this issue, a new approach is proposed. Large-scale atmospheric variables affecting the precipitation in study region and location attributes are suggested as features for regionalization by K-means cluster analysis. This allows independent validation of the identified regions for homogeneity using statistics computed from the observed precipitation. The summer monsoon rainfall (SMR) regions that are currently in use by India Meteorological Department (IMD) are shown to be heterogeneous. Subsequently the effectiveness of the proposed approach to regionalization is illustrated through application to India for delineating new SMR regions. Frequency distributions are identified to fit rainfall in the regions using L-moment-based goodness-of-fit test. Error in rainfall quantile estimates for the new regions is found to be significantly less than that estimated for the IMD SMR regions. The results show that the proposed approach to regional frequency analysis of precipitation is promising.Citation: Satyanarayana, P., and V. V. , Regional frequency analysis of precipitation using large-scale atmospheric variables,

The influence of a transverse velocity shear on the Rayleigh‐Taylor instability is investigated. It is found that a sheared velocity flow can substantially reduce the growth rate of the Rayleigh‐Taylor instability in the short wavelength regime (i.e., kL > 1 where L is the scale length of the density inhomogeneity), and causes the growth rate to maximize at kL < 1.0. Applications of this result to ionospheric phenomena [equatorial spread F (ESF) and ionospheric plasma clouds] are discussed. In particular, the effect of shear could account for, at times, the 100’s of km modulation observed on the bottomside of the ESF ionosphere and the km scale size wavelengths observed in barium cloud prompt striation phenomena.

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A general linear theory of the E x B instability is developed which considers an ambient electric field that is at an arbitrary angle to the density gradient and allows the electric field component parallel to the density gradient to be inhomogeneous. A differential equation is derived which describes the mode structure of the unstable waves in the direction of the inhomogeneities. The theory (1) includes ion inertia effects, (2) allows for arbitrary density and electric field profiles, and (3) is valid in the longwavelength regime, i.e., kvL < 1, where L is the width of the boundary layer. The main results of the analysis are as follows. First, the inhomogeneous velocity flow caused by the inhomogeneous electric field can stabilize the instability. Second, short-wavelength modes are preferentially stabilized over longer-wavelength modes. Third, the stabilization mechanism is associated with the velocity shear due to an x-dependent resonance [w -kvVv(x)] -1, where V•,(x) = -cE,:(x)/B, and not velocity shear terms explicitly proportional to oVdox or •o2Vdox 2. Fourth, the marginal stability criterion is weakly dependent on the magnitude of t,i,,/to. Applications of these results to ionospheric phenomena are discussed, viz., barium cloud striations and high-latitude F region irregularities. 1. fluid (region I) and the 'light' fluid perturbation to rise into the 'heavy' fluid (region II): the classic interchange phenomenon. Of course, if the direction of On/Ox or Ey were reversed then the density perturbation would be damped. The original study of the E x B instability was by Simon 425 [1963] and Hoh [1963], who applied it to laboratory gas discharge experiments. Subsequent to these first investigations, a considerable amount of research has been devoted to explaining ionospheric phenomena based upon this instability [Linson and Workman, 1970 and references therein; Simon, 1970; V61kandHaerendel, 1971;Perkins et al., 1973; Zabusky et al., 1973; $hiau and Simon, 1972; Perkins and Doles, 1975; $cannapieco et al., 1976; Chaturvedi and Ossakow, 1979; Keskinen and Ossakow, 1982]. Two areas of present interest concerning the instability are barium cloud striations (see, for example, the review papers by Ossakow [1979] and Ossakow et al. [1982] and the references therein) and the structuring of plasma 'blobs' in the high-latitude F region [Vickrey et al., 1980; Keskinen and Ossakow, 1982]. The purpose of this paper is to present a general theory of the E x B instability which considers an ambient electric field at an arbitrary angle to the density gradient and allows the electric field component parallel to the density gradient to be inhomogeneous. Some aspects of the problem have been treated by Perkins et al. [1973] and Perkins and Doles [1975]. Perkins and Doles [1975] made the important discovery that the sheared velocity flow (resulting from an inhomogeneous electric field parallel to the density gradient) can stabilize the instability. Furthermore, short-wavelength modes are preferentially stabilized over longer-wave...

A nonlocal theory of the Rayleigh‐Taylor instability, which includes the effect of a transverse velocity shear, is presented. A two‐fluid model is used to describe an inhomogeneous plasma under the influence of gravity and sheared equilibrium flow velocity and to derive a differential equation describing the generalized Rayleigh‐Taylor instability. An extensive parametric study is made in the collisionless and collisional regimes, and the corresponding dispersion curves are presented. The results are applied to the equatorial F region and to barium releases in the ionosphere.

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A theory of the current‐driven electrostatic ion cyclotron (EIC) instability in the collisional bottomside ionosphere is presented. It is found that electron collisions are destabilizing and are crucial for the excitation of the EIC instability in the collisional bottomside ionosphere. Furthermore, the growth rates of the ion cyclotron instability in the bottomside ionosphere maximize for k⊥ρ i ≥ 1, where 2π/k⊥ is the mode scale size perpendicular to the magnetic field and ρi the ion gyroradius. Realistic plasma density and temperature profiles typical of the high‐latitude ionosphere are used to compute the altitude dependence of the linear growth rate of the maximally growing modes and critical drift velocity of the EIC instability. The maximally growing modes correspond to observed tens of meter size irregularities, and the threshold drift velocity required for the excitation of EIC instability is lower for heavier ions (NO+, O+) than that for the lighter ions (H+). Dupree's resonance‐broadening theory is used to estimate nonlinear saturated amplitudes for the ion cyclotron instability in the high‐latitude ionosphere. Comparison with experimental observations is also made. It is conjectured that the EIC instability in the bottomside ionosphere could be a source of transversely accelerated heavier ions and energetic heavy‐ion conic distributions at higher altitudes.