Author

# R. Michael Jones

Other affiliations: University of Colorado Boulder, National Oceanic and Atmospheric Administration

Bio: R. Michael Jones is an academic researcher from Cooperative Institute for Research in Environmental Sciences. The author has contributed to research in topic(s): Gravity wave & Internal wave. The author has an hindex of 8, co-authored 26 publication(s) receiving 268 citation(s). Previous affiliations of R. Michael Jones include University of Colorado Boulder & National Oceanic and Atmospheric Administration.

##### Papers

More filters

••

TL;DR: In this article, an extension of Fermat's principle, in which the complex phase refractive index is used instead of only the real part, expresses both of these criteria and leads to a corresponding extension of Snell's law or of Haselgrove's equations to calculate the ray path.

Abstract: Standard ray-tracing programs do not calculate satisfactorily the reflection of LF radio waves from the ionosphere because they do not take losses into account. In lossy media, requiring the ray path to have a minimum attenuation in addition to a minimum wave interference gives a more accurate approximation to the full-wave solution. An extension of Fermat's principle, in which the complex phase refractive index is used instead of only the real part, expresses both of these criteria and leads to a corresponding extension of Snell's law or of Haselgrove's equations to calculate the ray path. Although such a path can have complex coordinates, only those with end points in real space are physically significant. An approximation, in which plane waves in the neighborhood of the receiver are assumed, solves the common ray-tracing problem of homing in on the receiver, a problem that is worse for ray tracing in complex space. Applying ray tracing in complex space to a plane wave incident on a plane stratified medium gives a result that agrees exactly with the result obtained by the phase integral method and that agrees satisfactorily with full-wave solutions above 30 kHz for all results shown.

49 citations

••

TL;DR: In this article, the authors used an Fe Boltzmann lidar to characterize the vertical wavelengths, periods, vertical phase speeds, frequency spectra, and vertical wave number spectra of stratospheric gravity waves from 30 to 50 km altitude.

Abstract: Five years of atmospheric temperature data, collected with an Fe Boltzmann lidar by the University of Colorado group from 2011 to 2015 at Arrival Heights, are used to characterize the vertical wavelengths, periods, vertical phase speeds, frequency spectra, and vertical wave number spectra of stratospheric gravity waves from 30 to 50 km altitudes. Over 1000 dominant gravity wave events are identified from the data. The seasonal spectral distributions of vertical wavelengths, periods, and vertical
phase speeds in summer, winter, and spring/fall are found obeying a lognormal distribution. Both the
downward and upward phase progression gravity waves are observed by the lidar, and the fractions of
gravity waves with downward phase progression increase from summer ~59% to winter ~70%.

37 citations

••

TL;DR: In this article, the spectral features of infrasound observed in the ionosphere and believed to be radiated by severe thunderstorms were modeled mathematically, and the dominant 2-5-min wave period was explained as an effect of atmospheric filtering; shorter periods are excessively attenuated by absorption in transit to ionosphere, and longer periods are attenuated in portions of the atmosphere where the waves are evanescent.

Abstract: We model mathematically the spectral features of infrasound observed in the ionosphere and believed to be radiated by severe thunderstorms. We explain the dominant 2–5‐min wave period as an effect of atmospheric filtering; shorter periods are excessively attenuated by absorption in transit to the ionosphere, and longer periods are attenuated in portions of the atmosphere where the waves are evanescent because their frequencies are below the acoustic cutoff. An observed spectral ’’fine structure’’ within the 2–5‐min band is explained in terms of resonant interactions between the waves and the atmospheric temperature structure. Accurate quantitative modeling of all these details of the storm‐to‐ionosphere transmission coefficient requires numerical integration of the acoustic‐gravity wave equation, including the effects of ground reflection, absorption, and partial reflections in the atmosphere.Subject Classification: [43]28.30.

28 citations

••

TL;DR: In this paper, the authors suggest that the strata of strong echo returns frequently revealed by remote-sensor records of the stably stratified planetary bound layer (PBL) represent the wavefronts of dissipative waves (viscous and thermal-conduction waves) excited by gravity-wave encounters with the PBL and the earth's surface.

Abstract: We suggest that the strata of strong echo returns frequently revealed by remote-sensor records of the stably stratified planetary bound layer (PBL) represent the wavefronts of dissipative waves (viscous and thermal-conduction waves) excited by gravity-wave encounters with the PBL and the earth's surface. The viscous waves appear to be more strongly forced and should therefore dominate the observations. This simple picture accounts for the following observed properties of the strata: 1) their nearly ubiquitous presence within the stably stratified PBL, 2) their nearly horizontal orientation, 3) the small spacing (some tens of meters, typically) separating the strata, 4) variability in that spacing in both height and time, and 5) the high shears and temperature gradients associated with the strata. Preliminary calculations of the energy fluxes and stresses associated with the wave motions, also presented here, suggest strongly that such waves are not mere curiosities of the PBL but reveal important...

27 citations

••

TL;DR: It is found that large values of E¯pm during wintertime occur when McMurdo is well inside the polar vortex, and E¯PM variations in winter are mainly due to variations of gravity wave generation in the troposphere and stratosphere and Doppler shifting by the mean stratospheric winds.

Abstract: Five years of Fe Boltzmann lidar's Rayleigh temperature data from 2011 to 2015 at McMurdo are used to characterize gravity wave potential energy mass density (Epm), potential energy volume density (Epv), vertical wave number spectra, and static stability N2 in the stratosphere 30-50 km. Epm (Epv) profiles increase (decrease) with altitude, and the scale heights of Epv indicate stronger wave dissipation in winter than in summer. Altitude mean E¯pm and E¯pv obey lognormal distributions and possess narrowly clustered small values in summer but widely spread large values in winter. E¯pm and E¯pv vary significantly from observation to observation but exhibit repeated seasonal patterns with summer minima and winter maxima. The winter maxima in 2012 and 2015 are higher than in other years, indicating interannual variations. Altitude mean N2¯ varies by ~30-40% from the midwinter maxima to minima around October and exhibits a nearly bimodal distribution. Monthly mean vertical wave number power spectral density for vertical wavelengths of 5-20 km increases from summer to winter. Using Modern Era Retrospective Analysis for Research and Applications version 2 data, we find that large values of E¯pm during wintertime occur when McMurdo is well inside the polar vortex. Monthly mean E¯pm are anticorrelated with wind rotation angles but positively correlated with wind speeds at 3 and 30 km. Corresponding correlation coefficients are -0.62, +0.87, and +0.80, respectively. Results indicate that the summer-winter asymmetry of E¯pm is mainly caused by critical level filtering that dissipates most gravity waves in summer. E¯pm variations in winter are mainly due to variations of gravity wave generation in the troposphere and stratosphere and Doppler shifting by the mean stratospheric winds.

24 citations

##### Cited by

More filters

••

TL;DR: Roll vortices may be loosely defined as quasi-two-dimensional organized large eddies with their horizontal axis extending through the whole planetary boundary layer (PBL), and their indirect manifestation is most obvious in so-called cloud streets as can be seen in numerous satellite pictures as mentioned in this paper.

Abstract: Roll vortices may be loosely defined as quasi two-dimensional organized large eddies with their horizontal axis extending through the whole planetary boundary layer (PBL). Their indirect manifestation is most obvious in so-called cloud streets as can be seen in numerous satellite pictures. Although this phenomenon has been known for more than twenty years and has been treated in a review by one of us (R.A.Brown) in 1980, there has been a recent resurgence in interest and information. The interest in ocena/land-atmosphere interactions in the context of climate modeling has led to detailed observational and modeling efforts on this problem. The presence of rolls can have a large impact on flux modelling in the PBL. Hence, we shall review recent advances in our understanding of organized large eddies in the PBL and on their role in vertical transport of momentum, heat, moisture and chemical trace substances within the lowest part of the atmosphere.

436 citations

••

TL;DR: In this article, the authors review the theory of acoustic-gravity waves, the interaction of such waves with the ionosphere, the experimental support for the existence of acoustic gravity waves in the upper atmosphere, and the role played by acoustic gravity wave in thermospheric dynamics.

Abstract: 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.

330 citations

••

TL;DR: In this article, a sparse-crop interaction theory is reformulated to allow calculation of the canopy resistance from measurements of foliage temperature and a submodel is introduced to describe eddy diffusion within the canopy which provides a simple, empirical simulation of the reported behavior obtained from a second-order closure model.

Abstract: One-dimensional, sparse-crop interaction theory is reformulated to allow calculation of the canopy resistance from measurements of foliage temperature. A submodel is introduced to describe eddy diffusion within the canopy which provides a simple, empirical simulation of the reported behavior obtained from a second-order closure model. The sensitivity of the calculated canopy resistance to the parameters and formulas assumed in the model is investigated. The calculation is shown to exhibit a significant but acceptable sensitivity to extreme changes in canopy aerodynamics, and to changes in the surface resistance of the substrate beneath the canopy at high and intermediate values of leaf area index. In very sparse crops changes in the surface resistance of the substrate are shown to contaminate the calculated canopy resistance, tending to amplify the apparent response to changes in water availability. The theory is developed to allow the use of a measurement of substrate temperature as an option to mitigate this contamination.

311 citations

••

TL;DR: The main source of turbulence may not be at the surface, but rather may result from shear above the surface inversion, sometimes preventing the formation of an inertial subrange as discussed by the authors.

Abstract: Atmospheric boundary layers with weak stratification are relatively well described by similarity theory and numerical models for stationary horizontally homogeneous conditions. With common strong stratification, similarity theory becomes unreliable. The turbulence structure and interactions with the mean flow and small-scale nonturbulent motions assume a variety of scenarios. The turbulence is intermittent and may no longer fully satisfy the usual conditions for the definition of turbulence. Nonturbulent motions include wave-like motions and solitary modes, two-dimensional vortical modes, microfronts, intermittent drainage flows, and a host of more complex structures. The main source of turbulence may not be at the surface, but rather may result from shear above the surface inversion. The turbulence is typically not in equilibrium with the nonturbulent motions, sometimes preventing the formation of an inertial subrange. New observational and analysis techniques are expected to advance our understanding of...

303 citations

••

TL;DR: The findings are consistent with model and historical analyses that suggest that, despite system feedbacks, decreased gs of upper canopy leaves at elevated [CO2] results in decreased transfer of water vapor to the atmosphere.

Abstract: Stomatal responses to atmospheric change have been well documented through a range of laboratory- and field-based experiments. Increases in atmospheric concentration of CO2 ([CO2]) have been shown to decrease stomatal conductance (gs) for a wide range of species under numerous conditions. Less well understood, however, is the extent to which leaf-level responses translate to changes in ecosystem evapotranspiration (ET). Since many changes at the soil, plant, and canopy microclimate levels may feed back on ET, it is not certain that a decrease in gs will decrease ET in rain-fed crops. To examine the scaling of the effect of elevated [CO2] on gs at the leaf to ecosystem ET, soybean (Glycine max) was grown in field conditions under control (approximately 375 μmol CO2 mol−1 air) and elevated [CO2] (approximately 550 μmol mol−1) using free air CO2 enrichment. ET was determined from the time of canopy closure to crop senescence using a residual energy balance approach over four growing seasons. Elevated [CO2] caused ET to decrease between 9% and 16% depending on year and despite large increases in photosynthesis and seed yield. Ecosystem ET was linked with gs of the upper canopy leaves when averaged across the growing seasons, such that a 10% decrease in gs results in a 8.6% decrease in ET; this relationship was not altered by growth at elevated [CO2]. The findings are consistent with model and historical analyses that suggest that, despite system feedbacks, decreased gs of upper canopy leaves at elevated [CO2] results in decreased transfer of water vapor to the atmosphere.

227 citations