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DOE OSTI2026

Process-oriented evaluation of quasi-stationary Rossby waves and their impact on surface air temperature extremes in dynamical downscaling over North America

Quasi-stationary Rossby waves are a crucial component of the general circulation and play a significant role in regional water and energy cycles, as well as in extreme events. However, process-oriented evaluation for Rossby waves is rarely performed for dynamical downscaling simulations. To close this gap, we evaluate three classes of dynamical downscaling approaches, with a focus on quasi-stationary Rossby waves and their impact on surface air temperature over North America during Northern Hemisphere summer. The three classes of models differ in the way large-scale forcing is provided: a limited-area model (LAM) constrained only by lateral boundary conditions, represented by RegCM4 from the North American branch of the Coordinated Regional Downscaling Experiment (NA-CORDEX), a LAM with spectral nudging to maintain consistency in large-scale dynamics with the forcing data, represented by the Weather Research and Forecasting (WRF) model simulation in NA-CORDEX, and a global variable-resolution model with smoothly varying grid spacings, represented by the Community Atmosphere Model version 5.4, with the Model for Prediction Across Scales (MPAS) as its dynamical core (CAM-MPAS). With no constraints on the atmospheric dynamics, CAM-MPAS exhibits several mean biases in the upper-level circulations over the Pacific Coast region: a weaker subtropical jet, a northward-shifted mid-latitude jet, and an overestimated southerly flow. With the lateral boundary constraint alone, RegCM4 also exhibits weaker jets and overestimated southerly winds off the West Coast. Rossby ray theory reveals that those wind biases direct incoming Rossby waves northward. The erroneously routed Rossby waves distort the relationship between the accumulation of wave activity over the US West Coast and surface temperature anomalies over the Southern Great Plains, which emerges approximately 4 d after the convergence of wave-activity flux in the ERA-Interim reanalysis. Furthermore, the response of heatwaves to the extreme wave activity flux is not reproduced by the two models, a serious drawback as a dynamical downscaling framework is expected to connect large-scale forcing to local-scale phenomena. The WRF model employing spectral nudging is largely free from the aforementioned problems. A pair of sensitivity simulations suggests that spectral nudging is the key to improving the dynamics of quasi-stationary Rossby waves and their impact on surface air temperature. Our results also demonstrate the effectiveness of Rossby wave diagnostics that allow for realistic background flows for assessing the credibility of dynamical downscaling over North America, where incoming Rossby waves propagate through complex circulation patterns before traveling across the continent.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1968

Nonlinear interactions of electromagnetic waves with a thermally generated cesium plasma.

The interaction of a large‐amplitude disturbing wave with a thermally generated, highly ionized cesium plasma has been investigated using a small‐amplitude sensing wave as a probe. The subsequent interaction between the disturbing and sensing waves is related to the plasma electron temperature. The plasma was contained in a magnetic field of 500–1000 G and had an electron plasma frequency near 10 GHz and an electron gyromagnetic frequency around 2 GHz. The sensing wave was a 10 GHz plane wave of approximately 1.5 mW input power and the disturbing wave was 7.5 GHz plane wave of about 1.2 W peak power. Measurements of the sensing‐wave transmitted power were made using standard microwave techniques. A notch filter in the sensing‐wave receiving circuit reduced the scattered disturbing‐wave interference to an immeasurably low level. Langmuir probes were used to detect disturbing‐wave modulation and to measure plasma temperatures and densities. Measurements of the interaction were correlated with a solution of the Boltzmann transport equation for a perturbed Maxwellian distribution function with binary Coulomb collisions.

Jack G Hewitt, Jr↗

NASA NTRS1974

Acoustic-gravity waves in the upper atmosphere

In this paper we review the theory of acoustic-gravity waves, the interaction of such waves with the ionosphere, the experimental support for the existence of such waves in the upper atmosphere, and the role played by acoustic-gravity waves in thermospheric dynamics. After a thorough discussion on the properties of acoustic-gravity waves in an ideal isothermal atmosphere, the effects produced by horizontal winds, sharp boundary discontinuities, and dissipative processes are discussed. The generation of these waves by stationary or moving sources is then treated. It is shown that the atmospheric response to a stationary impulse source can be described by the emission of three waves: acoustic, buoyancy, and gravity. These discussions are then followed by reviewing propagation effects in a realistic atmosphere for both free waves and guided waves. Recent numerical results are given. When acoustic-gravity waves propagate through the ionosphere, interaction between the wave and the ionosphere will take place. The physical processes involved in such an interaction are examined.

Yeh, K. C.↗

NASA NTRS1976

Whistler wave propagation in a large magnetoplasma

A large collisionless quiescent plasma source is developed for investigating the phase and amplitude distribution of antenna-launched whistler waves in a specified parameter regime relating wave frequency to electron cyclotron frequency. Wave dispersion is studied both by interferometer techniques with monochromatic waves and by propagation of short phase-coherent wave bursts. The wave damping mechanism is examined by propagating perfectly ducted whistler waves. The dispersion of single frequency waves and wave packets is demonstrated. Trough ducting for wave frequency to electron cyclotron frequency ratio greater than 1/2 is verified, and new eigenmodes in nonuniform plasmas at ratio values less than 1/2 are observed. It is shown that geometric effects due to ray divergence and wave refraction dominate over collisional damping.

Stenzel, R. L.↗

NASA NTRS1978

Excitation of low frequency waves by streaming ions via anomalous cyclotron resonance

The effect of a small population of streaming ions on low-frequency waves with frequencies below the ion cyclotron frequency is analyzed for three modes of interest: Alfven waves, magnetosonic waves, and ion-cyclotron waves. The instability mechanism is the anomalous cyclotron resonance of the waves with the streaming ions. Conditions for excitation of the three types of waves are derived and expressions for the growth rates are obtained. Excitation of Alfven waves is possible even if the ratio of the densities of the streaming ions to the thermal ions is very small. For magnetosonic waves, excitation can easily occur if waves are propagating parallel or nearly parallel to the ambient magnetic field. As for ion-cyclotron waves, it is found that for the ion-whistler branch the excitation is suppressed over a broader range of wave frequencies than for the fast magnetosonic branch.

Wu, C. S.↗

NASA NTRS1979

Characteristics of acoustic-gravity waves in a diffusively separated atmosphere

The effects of wave-induced diffusion on the characteristics of plane acoustic gravity waves in the earth's thermosphere are investigated by means of a two fluid model atmosphere in diffusive equilibrium. At wave periods greater than the shortest characteristic diffusion time for the minor gas, diffusion induced by the wave is considered to act to eliminate amplitude and phase differences between the wave-induced density fluctuations of individual gases and restore the perturbed fluid to diffusive equilibrium. Vertical diffusion is most important at large scale sizes, but horizontal diffusion dominates for horizontal wavelengths of less than several hundred kilometers. As a result of wave-induced diffusion, AE-C satellite measurements of neutral density fluctuations of thermospheric constituents are only compatible with relatively small scale internal gravity waves. Velocity and temperature differences for acoustic-gravity waves are greatest at periods near the mean collision time and diffusion time and lead to the dissipation of wave energy. The predictions of the theory are consistent with a high latitude, low altitude source for the medium scale waves and a more localized random source for the waves observed by AE-C.

Del Genio, A. D.↗

NASA NTRS1980

Wave propagation and transport in the middle atmosphere

The paper reviews the dynamics of wave propagation and wave transport for vertically propagating, planetary scale waves in the middle atmosphere. Such waves are divided into two major classes: extratropical planetary waves and equatorial waves. The most significant extratropical modes are the quasi-stationary Rossby waves, while the most significant equatorial modes are the Kelvin wave and the mixed Rossby-gravity wave. Both types of waves are capable of generating mean flow changes through wave-mean flow interaction.

Holton, J. R.↗

NASA NTRS1980

Ocean wave-radar modulation transfer functions from the West Coast experiment

Short gravity-capillary waves, the equilibrium, or the steady state excitations of the ocean surface are modulated by longer ocean waves. These short waves are the predominant microwave scatterers on the ocean surface under many viewing conditions so that the modulation is readily measured with CW Doppler radar used as a two-scale wave probe. Modulation transfer functions (the ratio of the cross spectrum of the line-of-sight orbital speed and backscattered microwave power to the autospectrum of the line-of-sight orbital speed) were measured at 9.375 and 1.5 GHz (Bragg wavelengths of 2.3 and 13 cm) for winds up to 10 m/s and ocean wave periods from 2-18 s. The measurements were compared with the relaxation-time model; the principal result is that a source of modulation other than straining by the horizontal component of orbital speed, possibly the wave-induced airflow, is responsible for most of the modulation by waves of typical ocean wave period (10 s). The modulations are large; for unit coherence, spectra of radar images of deep-water waves should be proportional to the quotient of the slope spectra of the ocean waves by the ocean wave frequency.

Wright, J. W.↗

NASA NTRS1985

A ray tracing model of gravity wave propagation and breakdown in the middle atmosphere

Lindzen (1981, 1984) has considered the effects of monochromatic, steady gravity waves propagating into the upper atmosphere. These waves reach such large amplitudes in the mesosphere that they become convectively unstable. The wave is effectively dissipated by the convection, and the pseudomomentum carried by the wave is transferred to the basic flow. The net effect is to accelerate the background flow to the phase speed of the breaking gravity wave. Schoeberl et al. (1983) have discussed modifications to Lindzen's parameterization. The present paper has the objective to develop a type of parameterization scheme for wave breaking that, in principle, can handle lateral wave propagation. Ray tracing is used to follow the gravity wave packets through varying wind conditions. The theory considered uses both the propagation properties of the wave packet and the concept of the conservation of wave action density to determine the local amplitude and position of the wave packet.

Schoeberl, M. R.↗

NASA NTRS1986

Steepened magnetosonic waves in the high beta plasma surrounding Comet Giacobini-Zinner

Studies of intense hydromagnetic waves at Giacobini-Zinner are extended to investigate the mode and direction of wave propagation. Simultaneous high-resolution measurements of electron density fluctuations demonstrate that long period waves propagate in the magnetosonic mode. Principal axis analyses of the long period waves and accompanying partial rotations show that the sum of the wave phase rotations is 360 deg, indicating that both are parts of the same wave oscillation. The time sequence of the steepened waveforms observed by ICE shows that the waves must propagate towards the Sun with Cph less than Vsw. Observations are consistent with wave generation by resonant ion ring or ion beam instability which predicts right-hand polarized waves propagating in the ion beam (solar) direction. The large amplitudes and small scale sizes of the cometary waves suggest that rapid pitch-angle scattering and energy transfer with energetic ions should occur. Since the waves are highly compressive, first-order Fermi acceleration is forecast.

Tsurutani, B. T.↗

NASA NTRS1986

The behavior of planetary wave 2 in preconditioned zonal flows

The response of linear planetary wave 2 to changes in the isentropic zonally symmetric distribution of potential vorticity (PV) is investigated numerically. Wave 2 is sensitive to the width and position of a region where the meridional derivative of PV is weak, denoted the 'surf zone', in the middle stratosphere. A narrow surf zone leads to an amplification of wave 2, and confines some of its Eliassen-Palm wave activity in high latitudes. For wider surf zones the wave activity is concentrated near the associated critical surface, and the amplitude of the wave decreases. Large changes in the wave amplitude and in the distribution of its activity are associated with the subtle changes in the zonal winds produced by modest modifications in the distribution of PV. Basic states that include regions of reversed meridional gradients of PV lead to wave overreflection and strong poleward focusing of wave activity. The amplitude of wave 2 is enhanced in the presence of negative gradients, with large responses occurring for eastward traveling waves.

Robinson, Walter A.↗

NASA NTRS1987

Effect of current on spectrum of breaking waves in water of finite depth

This paper presents an approximate method to compute the mean value, the mean square value and the spectrum of waves in water of finite depth taking into account the effect of wave breaking with or without the presence of current. It is assumed that there exists a linear and Gaussian ideal wave train whose spectrum is first obtained using the wave energy flux balance equation without considering wave breaking. The Miche wave breaking criterion for waves in finite water depth is used to limit the wave elevation and establish an expression for the breaking wave elevation in terms of the elevation and its second time derivative of the ideal waves. Simple expressions for the mean value, the mean square value and the spectrum are obtained. These results are applied to the case in which a deep water unidirectional wave train, propagating normally towards a straight shoreline over gently varying sea bottom of parallel and straight contours, encounters an adverse steady current whose velocity is assumed to be uniformly distributed with depth. Numerical results are obtained and presented in graphical form.

Tung, C. C.↗

NASA NTRS1988

Development of a satellite SAR image spectra and altimeter wave height data assimilation system for ERS-1

The applicability of ERS-1 wind and wave data for wave models was studied using the WAM third generation wave model and SEASAT altimeter, scatterometer and SAR data. A series of global wave hindcasts is made for the surface stress and surface wind fields by assimilation of scatterometer data for the full 96-day SEASAT and also for two wind field analyses for shorter periods by assimilation with the higher resolution ECMWF T63 model and by subjective analysis methods. It is found that wave models respond very sensitively to inconsistencies in wind field analyses and therefore provide a valuable data validation tool. Comparisons between SEASAT SAR image spectra and theoretical SAR spectra derived from the hindcast wave spectra by Monte Carlo simulations yield good overall agreement for 32 cases representing a wide variety of wave conditions. It is concluded that SAR wave imaging is sufficiently well understood to apply SAR image spectra with confidence for wave studies if supported by realistic wave models and theoretical computations of the strongly nonlinear mapping of the wave spectrum into the SAR image spectrum. A closed nonlinear integral expression for this spectral mapping relation is derived which avoids the inherent statistical errors of Monte Carlo computations and may prove to be more efficient numerically.

Hasselmann, Klaus↗

NASA NTRS1990

Wave-interactions in supersonic and hypersonic flows

Work completed under the current grant comprises the start of a theoretical and computational attack on the subharmonic route to secondary instabilities in compressible flows. The total flow field in this problem is made up of the following components: (1) a steady streamwise mean boundary layer flow which depends only on the normal space component y; (2) a two-dimensional time dependent T-S wave which moves with wavespeed c and has no spanwise dependence; and (3) a fully three-dimensional, time dependent T-S wave whose streamwise wavenumber is half of the streamwise wavenumber associated with the two-dimensional T-S wave in b. If a frame of reference is adopted which moves with the wavespeed c of the 2-D T-S wave, the time dependence of this portion of the flow can be eliminated. The effective steady mean flow in this problem is now the sum of the original parallel steady mean flow and the initial 2-D T-S instability. Dependence on the streamwise coordinate x in this mean flow can be extracted by assuming normal mode expansions involving complex exponentials and the streamwise wavenumber a. However, it is important to note that, because this is a wave-wave interaction problem, unlike the usual linear instability case, both the complex exponential, and its complex conjugate, must be retained in describing the 2-D T-S wave. The role of the perturbation to the steady mean flow is now played by the 3-D time dependent T-S wave. In treating this wave, normal modes in the streamwise and spanwise directions and time may be used. Consistent with the subharmonic nature of this transition route, the streamwise wavenumber is a/2, and complex conjugates of the complex exponential must be employed. This is not the case with the modes giving z and t dependence with wavespeed o and spanwise wavenumber B as the effective mean flow quantities are independent of z and their time dependence is accounted for by the moving frame of reference. Consequently, the wave-wave interaction which will produce mean flow modification occurs only through the streamwise exponentials.

Lakin, William D.↗

NASA NTRS1991

The effects of transience on the propagation of stratospheric planetary waves

The propagation of planetary-scale Rossby waves in the stratosphere is investigated in a linear, time-dependent, primitive equation model. Two distinct maxima in the convergence of the Eliassen-Palm flux (EP flux) are found for steady and for transient waves in a variety of realistic northern hemisphere, winter season, zonal flows; one below the stratospheric polar jet and the other north of the zero wind line. These maxima appear at higher altitudes for wave 1 than for wave 2, especially in low latitudes. Different mechanisms cause the formation of these two maxima. The confinement of wave activity in high latitudes is mainly due to the dissipation of waves in that region under non-WKBJ conditions. The maximum in lower latitudes is related to the absorption of Rossby waves near their critical lines. For wave 2, the intensity of the high latitude maximum is sensitive to the transience of the wave forcing at the tropopause, while for wave 1 this sensitivity is reduced. For both waves the low latitude maximum shifts northward with increasing transience.

Chen, Ping↗

NASA NTRS1991

Parameterization of planetary wave breaking in the middle atmosphere

A parameterization of planetary wave breaking in the middle atmosphere has been developed and tested in a numerical model which includes governing equations for a single wave and the zonal-mean state. The parameterization is based on the assumption that wave breaking represents a steady-state equilibrium between the flux of wave activity and its dissipation by nonlinear processes, and that the latter can be represented as linear damping of the primary wave. With this and the additional assumption that the effect of breaking is to prevent further amplitude growth, the required dissipation rate is readily obtained from the steady-state equation for wave activity; diffusivity coefficients then follow from the dissipation rate. The assumptions made in the derivation are equivalent to those commonly used in parameterizations for gravity wave breaking, but the formulation in terms of wave activity helps highlight the central role of the wave group velocity in determining the dissipation rate. Comparison of model results with nonlinear calculations of wave breaking and with diagnostic determinations of stratospheric diffusion coefficients reveals remarkably good agreement, and suggests that the parameterization could be useful for simulating inexpensively, but realistically, the effects of planetary wave transport.

Garcia, Rolando R.↗

NASA NTRS1991

Effects of the Gulf Stream on ocean waves

In the present study a third-generation numerical wave model is used to study effects of a straight Gulf Stream ring on ocean waves in swell and storm conditions. The model accounts for all relevant processes of propagation, generation, and dissipation of the waves (including current effects) without imposing a priori restraints on the spectral development of the waves. The dominating mechanism affecting the waves appears to be current-induced refraction even though the short-crestedness of the incoming waves tends to mask its effects (also in swell conditions). Depending on wind and wave conditions, refraction may trap locally generated waves in the straight Gulf Stream or it may reflect wave energy back to the open ocean. In the Gulf Stream ring, refraction induces a considerable variation in significant wave height and short-crestedness, but it hardly affects the mean wave direction. In storm conditions the processes of generation and dissipation are considerably enhanced in countercurrent situations and reduced following-current situations.

Holthuijsen, L. H.↗

NASA NTRS1991

Planetary-scale waves in the Southern Hemisphere winter and early spring stratosphere - Stability analysis

A barotropic stability model linearized about a zonally symmetric flow is used to examine the stability characteristics of horizontal zonal-mean flow profiles representative of the Southern Hemisphere middle stratosphere during winter and early spring, with emphasis on periods when planetary wave growth appears confined to the stratosphere. Unstable modes of eastward-travelling waves 2 and 3 are found to have period sand spatial structures, similar to observations. Wave-2 and wave-3 momentum fluxes are similar in observations and model results and are consistent with the transfer of kinetic energy from the zonal-mean flow to the wave. When a barotropic model with a zonally symmetric basic flow is used, wave 3 is usually most unstable. Including a stationary wave 1 in the basic flow destabilizes both wave 2 and wave 3, but has little effect on their periods or spatial structures. The similarity between observed fields and model results in a number of cases when wave 2 appears to grow within the stratosphere suggests that in situ instabilities play a role in the evolution of the eastward-traveling wave-2 characteristic of the Southern Hemisphere winter and early spring stratosphere.

Manney, G. L.↗