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Hanli Liu

General Information

Hanli Liu

Scientist III
Gravity Waves

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: CG1 - 2160
Telephone: 303-497-1564
Home Page

Research Focus FY08:

Gravity waves play an important role in the coupling of various atmospheric regions. Therefore, the study of gravity waves is a focal point of lower, middle, and upper atmospheric research, being of strong inter-disciplinary interest.

Outstanding Questions and Problems: There are outstanding questions in the gravity wave excitation mechanism, source distribution and variability, wave impact in the lower, middle and upper atmosphere, and parameterization of wave source and impact in global scale models. Flow over topography has been a classical example of gravity wave excitation and has been extensively studied. However, surface drag from orographic wave parameterizations in general circulation models is still problematic and hinders our ability to correctly resolve planetary waves in whole-atmosphere models.

Mesoscale modeling of gravity waves using realistic orography and weather condition and observations from campaign studies of orographic waves should be used to improve the quantification of the process. Gravity waves generated from realistic convective systems and from spontaneous adjustment due to geostrophic imbalance, as well as from complex interactions of these systems are still poorly understood and not well quantified. Petascale computing capabilities afforded by the upcoming NCAR Supercomputing Center will make possible high-resolution simulations of such systems, which will help to improve understanding of the gravity waves generated.

The gravity waves affect atmospheric processes in the lower, middle and upper atmosphere. The transport and deposition of momentum can affect the middle and upper atmosphere circulation, and wave breaking can generate turbulence that can affect aviation, constituents mixing, specifically mass exchange between upper troposphere/ lower stratosphere and mesosphere/lower thermosphere, as well as heating and cooling in the upper atmosphere. Gravity waves may also affect space weather by seeding ionospheric irregularities.

The NCAR - University Opportunity: The vast spatial and temporal existence of gravity waves has important implications for the atmospheric dynamics and thermal/compositional structure from mesoscales to global scales. The multiscale nature of the gravity waves poses a stiff challenge to the physical understanding and quantification of these waves in both observations and numerical models. Integrated mesoscale modeling of these processes, extending from the wave sources to the impact region, is needed to address these problems. The integrated model can also support observational campaign studies of gravity waves as well as the validation of gravity wave parameterization. Such efforts will promote collaboration across the ESSL scientific divisions and between NCAR and the university community.

Satellite observations can provide valuable information on the global distribution and variability of gravity waves. The Constellation Observing System for Meteorology Ionosphere & Climate (COSMIC) radio occultation measurement is being used to derive the gravity wave variance and its global distribution and temporal variation. New algorithms will be explored to infer more specific gravity wave characteristics from COSMIC measurements. Data assimilation techniques will be tested to quantify global gravity wave impact by combining satellite observations of temperature, wind and the Whole-Atmosphere Community Climate Model (WACCM) simulations.


Community Service FY08:

  • Associate Editor Journal of Geop0hysical Research - Space Physics
  • CEDAR Science Steering Committee
  • Graduate Research Advisor & Thesis Member: Chihoko Yamashita, University of Colorado, Boulder

Scientific Talks FY08:

  • Gravity waves from the Nest Regional Climate Model (Anhui, CHN, 08/2008)
  • Troposphere-thermosphere coupling by nonmigrating tides (Montreal, CAN, 07/2008)
  • The quasi-biennial, annual, and semi-annual oscillations in the migrating diurnal tide (Montreal, CAN, 07/2008)
  • Dynamical variability during 2006 SSW (Midway, UT USA, 06/2008)
  • Atmospheric gravity waves: Apply classroom physics to research (Midway, UT USA, 06/2008)
  • Gravity waves from the Nest Regional Climate Model (invited) (Crete, GRC, 05/2008)
  • Neutral and plasma variability in the F region from the dissipation of gravity waves from convection (Crete, GRC, 05/2008)
  • Modeling the ring structures in the OH airglow layer from gravity waves excited by convection near Fort Collins, Colorado (Crete, GRC, 05/2008)
  • Simulations of the midnight temperature maximum with the NCAR TIME-GCM (Crete, GRC, 05/2008)
  • Thermospheric structures and variabilities from the NCAR Whole Atmosphere Community Climate Model (WACCM) (New Orleans, LA USA, 01/2008)
  • Assessment of the non-hydrostatic effect in general circulation models (GCMs) (San Francisco, CA USA, 12/2007)
  • Analysis of mid-latitude neutral wind in the lower thermosphere: Comparison of Fall and Spring equinoxes (San Francisco, CA USA, 12/2007)
  • Interannual variability in the effects of energetic particle precipitation (EPP) on the stratosphere (San Francisco, CA USA, 12/2007)
  • On the existence and excitation of eastward propagating quasi-two day waves in the MLT (San Francisco, CA USA, 12/2007)
  • Seasonal variations of mesospheric Fe layers at Rothera and comparison to the South Pole (San Francisco, CA USA, 12/2007)
  • Whole Atmosphere Community Climate Model (WACCM): Recent development and research at HAO (Washington, DC USA, 11/2007)
  • Sun-Earth coupling by energetic particles (Kyoto, JPN, 10/2007)
  • Wind balance in the mesosphere and lower thermosphere (Kyoto, JPN, 10/2007)

Publications FY08:

Deng, Y., A. D. Richmond, A. J. Ridley, and H.-L. Liu, Assessment of the non-hydrostatic effect on the upper atmosphere using a general circulation model (GCM), Geophys. Res. Lett., 35, L01104, doi:10.1029/2007GL032182, 2008.

Liu, X., J. Xu, H.-L. Liu, and R. Ma, Nonlinear interactions between gravity waves with different wavelengths and diurnal tide, J. Geophys. Res., 113, doi:10.1029/2007JD009136, 2008.

Tian, F., J. Kasting, H.-L. Liu, and R. G. Roble, Hydrodynamic planetary thermosphere model. I: The response of the Earth's thermosphere to extreme solar EUV conditions and the significance of adiabatic cooling, J. Geophys. Res.-Planetary, 113, E05008, 10.1029/2007JE002946, 2008.

Wu, Q., D. A. Ortland, T. L. Killeen, R. G. Roble, M. E. Hagan, H.-L. Liu, S. C. Solomon, J. Xu, W. R. Skinner, and R. J. Niciejewski, Global distribution and inter-annual variations of mesospheric and lower thermospheric neutral wind diurnal tide, Part 1: Migrating tide, J. Geophys. Res., 113, A05308, 10.1029/2007JA012542, 2008.

Wu, Q., D. A. Ortland, T. L. Killeen, R. G. Roble, M. E. Hagan, H.-L. Liu, S. C. Solomon, J. Xu, W. R. Skinner, and R. J. Niciejewski, Global distribution and inter-annual variations of mesospheric and lower thermospheric neutral wind diurnal tide, Part 2: Non-migrating tide, J. Geophys. Res., 113, A05309, 10.1029/2007JA012543, 2008.

Zhao, Y., M. J. Taylor, H.-L. Liu, and R. G. Roble, Seasonal oscillations in mesospheric temperatures at low-latitudes, J. Atmos. Solar Terr. Phys., 69, 2367-2378, 2007.

Li, T., C.-Y. She, H.-L. Liu, T. Leblanc, and I. S. McDermid, Sodium lidar observed strong inertia-gravity wave activities in the mesopause region over Fort Collins, CO (41N, 105W), J. Geophys. Res., 112, 10.1029/2007JD008681, 2008.

Yuan, T., C.-Y. She, D. A. Krueger, F. Sassi, R. R. Garcia, R. G. Roble, H.-L. Liu, and H. Schmidt, Climatology of mesopause region temperature, zonal wind and meridional wind over Fort Collins, CO (41N, 105W), J. Geophys. Res., 113, D03105, 2008.

Liu, H.-L., T. Li, C.-Y. She, J. Oberheide, Q. Wu, M. E. Hagan, J. Xu, R. G. Roble, M. G. Mlynczak, J. M. Russell III, Comparative study of short term tidal variability, J. Geophys. Res., 112, doi:10.1029/2007JD008542, 2007.

Xu, J., A. K. Smith, W. Yuan, H.-L. Liu, Q. Wu, M. G. Mlynczak, and J. M. Russell III, The global structure and long term variations of zonal mean temperature observed by TIMED/SABER, J. Geophys. Res., 112, 10.1029/2007JD008546, 2007.

Liu, H.-L., On the large wind shear and fast meridional transport above the mesopause, Geophys. Res. Lett., 34, L08815, doi:10.1029/2006GL028789, 2007.

Richter, J. H., M. A. Geller, R. R. Garcia, H.-L. Liu, and F. Zhang, Report on the gravity wave retreat, Stratospheric Processes and Their Role in Climate (SPARC) Newsletter, No 28, 26-27, 2007.

Li, T., C.-Y. She, H.-L. Liu, and M. T. Montgomery, Evidence of a gravity wave breaking event and the estimation of the wave characteristics from sodium lidar observation over Fort Collins, CO (41N 105W), 34, L05815, doi:10.1029/2006GL028988, Geophys. Res. Lett., 2007.

Xu, J., H.-L. Liu, W. Yuan, A. K. Smith, R. G. Roble, C. J. Mertens, J. M. Russell III, and M. G. Mlynczak, Mesopause structure from TIMED/SABER observations , J. Geophys. Res. (Atmosphere), 112, D09102, doi:10.1029/2006JD007711, 2007.

Li, T., C.-Y. She, S. E. Palo, Q. Wu, H.-L. Liu, and M. L. Salby, Coordinated Lidar and TIMED observations of the quasi-two-day wave during August 2002-2004 and possible quasi-biennial oscillation influence, Adv. Space Res., 41, 1462-1470, 2008.

Liu, H.-L., Spectral Properties of one-dimensional diffusive systems subject to stochastic forcing, J. Atmos. Sci., 64, 579-593, 2007.