ESSL LAR

Jadwiga 'Yaga' Richter

 

Scientist I
TIIMES - CGD
Gravity Waves

 

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: ML - 305
Telephone: 303-497-1718
Email: jrichter@ucar.edu
Home Page | FY2007 Abstracts

Jadwiga Richter
 

Project Summary:

 

Gravity Waves - Rayleigh damping
Click on picture to view the entire figure.


Figure 1. Two-dimensional (ω, k) power spectra of vertical velocity in dB near the model top for the Rayleigh damping (RD), diffusive damping (DD), vertical velocity damping (WD), and no damping (ND) simulations.

Gravity wave damping in the WRF model

The Weather Research and Forecast Model (WRF) is a state of the art model that can be used for studies of convection and mesoscale systems. WRF would be an excellent model for studies of gravity waves generated by convection and mesoscales systems as it can be run over large areas and with realistic background conditions. However, the current top boundary condition in WRF causes a lot of wave reflection back into the model domain, making WRF unsuitable for gravity wave studies.

In collaboration with J. Klemp (MMM), J. Dudhia (MMM), J. Richter (CGD), and H.-L. Liu (HAO), TIIMES visitor, Alex Hassiotis (graduate student, Pennsylvania State University) explored various upper boundary conditions in WRF that would expand WRF’s gravity waves damping capabilities. Hassiotis performed two-dimensional idealized squall line simulations with a) sponge layer using horizontal diffusion, b) Rayleigh damping, and c) vertical-velocity damping. He found, that when a broad spectrum of gravity waves is present, as is the case with convective sources, the Rayleigh and diffusive damping schemes in WRF remove only a portion of the wave spectrum. In contrast, vertical-velocity damping with a sufficiently high damping coefficient proved highly effective at dissipating almost the complete spectrum of waves (Figure 1).

Gravity Waves - Brunt-Vaisala frequency
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Figure 2. Brunt-Vaisala frequency (s-¹) and maximum wind shear allowed by dynamic stability (in parentheses, unit: ms-¹ km-¹) from TIME-GCM simulations under September equinox (a) and December solstice (b) conditions at 0° longitude. Contour interval: 0.0025 s-¹> (5 ms-¹ km-¹). Shaded region: N > 0.03-¹ (Smax > 60 ms-¹ km-¹). (c) Profiles of maximum wind shear allowed at 18 longitudes (20° apart) and 2.5°N for day 355. The profiles are in good agreement with the measured maximum wind shears.

Vertical velocity damping looks promising for permanent implementation in WRF for gravity wave damping, however tests with real-data cases must be still performed to confirm this finding.

 

Large Wind Shear and Fast Meridional Transport Above the Mesopause

Unexpectedly strong winds/shears and fast meridional transport above the mesopause have been revealed from previous rocket and satellite observations. These strong winds/shears and fast meridional transport are not accounted for in current global models. In this study we examine the possible causes using analytical and diagnostic studies.

Using Richardson number criteria for dynamic stability, H.-L. Liu (HAO) estimated the maximum wind shears allowable by the background static stability, which peaks above the mesopause. These maximum shears are in general agreement with the large wind shears inferred from the rocket measurements at low and mid-latitudes, indicating the close relationship between the latter and the the stability constraint set by the background atmosphere (Figure 2). The large shear may come from gravity waves, whose vertical wavelength decreases in the region of maximum static stability. Diagnostic calculations also indicate that the meridional transport in this region may not be well understood solely by examining the mean meridional circulation, and large amplitude tides/planetary waves can play an important role in the bulk transport of tracers. Strong stochastic winds, presumably due to gravity waves, do not seem to significantly change the large scale pattern of the transport but may extend the range of the tracer movement.

H.-L. Liu will work with university collaborators to examine lidar/radar observations of winds, temperature, and gravity wave activities to test the theoretical understanding.
 

Community Service:

  • Advisor on Graduate Research: Alex Hassiotis, , Pennsylvania State University, University Park, PA USA
  • Advisor on Graduate Research: Alex Hassiotis, , Pennsylvania State University, University Park, PA USA
 

TIIMES External Collaborators:

Joan Alexander, NorthWest Research Associates / CoRA
Andreas Dornbrack, Institut fur Physik der Atmosphare
James Doyle, Naval Research Lab
Timothy Dunkerton, NorthWest Research Associates
Stephen Eckerman, Naval Research Lab
David Fritts, Colorado Research Associates
Kenneth Gage, National Oceanic & Atmospheric Administration (NOAA) - ESRL
Chester Gardner, University of Illinois
Marvin Geller, Stony Brook University
Kevin Hamilton, University of Hawaii
Todd Lane, The University of Melbourne
Theodore Shepherd, University of Toronto
Ronald Smith, Yale University
Robert Vincent, University of Adelaide
Dong Wu, Jet Propulsion Laboratory (JPL) - NASA
Fuqing Zhang, Texas A&M University
 

Publications:

Richter, J. H., M. A. Geller, R. R. Garcia, F. Zhang, 2007: Report on the Gravity Wave Retreat. SPARC Newsletter, 28, 26-27.

Alexander, M. J., J. H. Richter, B. R. Sutherland, 2006: Generation and trapping of gravity waves from convection with comparison to parameterization. J. Atmos. Sci., 63, 2963-2977.