HAO 2011 Profiles In Science: Dr. Hanli Liu

Contact:

Dr. Hanli Liu is a Scientist III at the High Altitude Observatory, National Center for Atmospheric Research. He received a B.S. in Fluid Mechanics from the University of Science and Technology of China, and a Ph.D. in Atmospheric and Space Physics from the University of Michigan. He came to the Observatory in 1997 as a postdoctoral researcher, and joined the scientific staff in 1999. His research includes: theoretical, numerical, and interpretive studies of the dynamics, structure, and solar/terrestrial responses of the Earth's middle and upper atmosphere; coupling of different atmospheric regions on global and regional scales; atmospheric waves; geophysical turbulence and self-organized critical phenomena. He is leading the thermosphere/ionosphere extension of the Whole Atmosphere Community Climate Model (WACCM).

Dr. Hanli Liu has a personal webpage at http://people.hao.ucar.edu/liuh/.

Publications

(1)
Tan, B., X. Chu, H.-L. Liu, C. Yamashita, and J. M. Russell III. Patterns of teleconnection among different latitudes in both hemispheres and different altitudes from 15 to 110 km derived from SABER and WACCM Submitted to J. Geophys. Res.

Abtract: Correlation patterns of atmospheric temperature across altitudes and latitudes, broadly referred to as teleconnection, are derived from temperature measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Teleconnection structures for time periods with and without Sudden Stratospheric Warmings (SSWs) display qualitatively similar patterns. These patterns are reproduced in simulations using the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model (WACCM). The teleconnection patterns are related to the residual circulations according to the simulations, and they reveal that the three circulations in the stratosphere, mesosphere and lower thermosphere all respond to temperature anomalies in the northern polar stratosphere. It is also found that the altitudes of the teleconnection patterns in the southern polar mesosphere and lower thermosphere display inter-annual variations.

(2)
Xue, X., H.-L. Liu, and X. Dou. Parameterization of inertial gravity waves and generation of quasi-bienniel oscillation. Submitted J. Geophys. Res.

Abtract: In this work we extend the gravity wave parameterization scheme currently used in the Whole Atmosphere Community Climate Model (WACCM), which is based upon Lindzen's linear saturation theory, by including the Coriolis effect to better describe inertia-gravity waves (IGW). WACCM simulations are performed with the new parameterization to study the generation of equatorial oscillations of the zonal mean zonal winds by including a spectrum of IGWs, and the parametric dependence of the wind oscillation on the IGWs and the effect of the new scheme. These simulations demonstrate that the parameterized IGW forcing from the standard and the new scheme are both capable of generating equatorial wind oscillations with a downward phase progression in the stratosphere using the standard spatial resolution settings in the current model. The period of the 14 oscillation is dependent on the strength of the IGW forcing, and the magnitude of the oscillation is dependent on the width of the wave spectrum. The new parameterization affects the wave breaking level and acceleration rates mainly through changing the critical level. Quasi-biennial oscillations (QBO) can be internally generated with the proper selection of the parameters of the scheme. The characteristics of the wind oscillations thus generated are compared with the observed QBO. These experiments demonstrate the need to parameterize IGWs for generating the QBO in General Circulation Models.

(3)
Yue, J., H.-L. Liu and L. C. Chang. Numerical investigation of the Quasi-two-day wave in the lower thermosphere. Submitted to J. Geophys. Res.

Abtract: The zonal wavenumber 3 planetary wave with about 2 days period (QTDW) is a recurrent wave feature in the mesosphere and lower thermosphere (MLT). The QTDW exhibits strong seasonal variability with peak amplitudes after summer solstice. In late January/early February, satellites also discovered two strong enhancements of the QTDW in meridional wind, one peak at summer mid-latitudes near 90 km and the other in the tropical lower thermosphere. This double-peak characteristic of the QTDW meridional component is numerically investigated by the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) with the QTDW forcing prescribed at the lower model boundary. Baroclinic/barotropic instability is capable of amplifying the QTDW, manifesting as EP flux divergence in the summer mesosphere. Without the direct contribution from baroclinic/barotropic instability, the simulated QTDW response in lower thermosphere temperature and horizontal wind resembles that of the (3, 0) Rossby-gravity normal mode. In the summer middle atmosphere, the wave amplitude grows substantially like internal wave in the regions of large refractive index. As the wave amplitude growth ceases near mesopause where the zonal wind reverses direction, the QTDW reaches its maximum amplitude, displaying an enhanced meridional component in the tropical lower thermosphere. Above the mesopause, the QTDW is damped by molecular diffusion. Compared to a prior model run, the propagation of the QTDW can also be prohibited by a self-generated critical layer in a strong thermospheric easterly wind. In addition, a direct contribution from the migrating diurnal tide to the QTDW amplitude in the MLT is found. This is largely attributed to the change of the background zonal wind caused by the tide, thus leading to the increase of the QTDW refractive index in the summer middle atmosphere.

(4)
Chang, L. C., W.E. Ward, S. E. Palo, J. Du, D.-Y Wang, H.-L. Liu, M. E. Hagan, Y. Portnyagin, J. Oberheide, L.P. Goncharenko, T. Nakamura, P. Hoffmann, W. Singer, P. Batista, B. Clemesha, A.H. Manson, D.M. Riggin, C.-Y. She, T. Tsuda, and T. Yuan. Comparison of Diurnal Tide in Models and Ground-Based Observations during the 2005 Equinox CAWSES Tidal Campaign.J. Atmos. Solar Terr. Phys., in press, doi:10.1016/j.jastp.2010.12.010.

Abtract: In this study, ground-based observations of equinox diurnal tide wind fields from the first CAWSES Global Tidal Campaign are compared with results from five commonly used models, in order to identify systematic differences. WACCM3 and Extended CMAM are both self-consistent general circulation models, which resolve general climatological features, while TIME-GCM can be forced to approximate specific conditions using reanalysis fields. GSWM is a linear mechanistic model; while GEWM is an empirical model derived from ground-based and satellite observations. The models resolve diurnal tides consistent in latitudinal structure with observations, dominated by the upward propagating (1,1) mode. There is disagreement in the magnitudes of the tidal amplitudes and vertical wavelengths, while differences in longitudinal tidal variability indicate differences in the nonmigrating tides in the models. These points suggest inconsistencies in model forcing, dissipation, and background winds that must be examined as part of a coordinated effort from the modeling community.

(5)
Chau, J. L., L. P. Goncharenko, B. G. Fejer, and H.-L. Liu. Equatorial and Low Latitude Ionospheric Effects During Sudden StratosphericWarming Events. In press, Space Sci. Rev., 158, doi:10.1007/s11214-011-9797-5.

Abtract: There are several external sources of ionospheric forcing, including these are solar wind-magnetospheric processes and lower atmospheric winds and waves. In this work we review the observed ion-neutral coupling effects at equatorial and low latitudes during large meteorological events called sudden stratospheric warming (SSW). Research in this direction has been accelerated in recent years mainly due to: (1) extensive observing campaigns, and (2) solar minimum conditions. The former has been instrumental to capture the events before, during, and after the peak SSW temperatures and wind perturbations. The latter has permitted a reduced forcing contribution from solar wind-magnetospheric processes. The main ionospheric effects are clearly observed in the zonal electric fields (or vertical E×B drifts), total electron content, and electron and neutral densities.We include results from different ground- and satellite-based observations, covering different longitudes and years. We also present and discuss the modeling efforts that support most of the observations. Given that SSW can be forecasted with a few days in advance, there is potential for using the connection with the ionosphere for forecasting the occurrence and evolution of electrodynamic perturbations at low latitudes, and sometimes also mid latitudes, during arctic winter warmings.

(6)
Lei, J., J. M. Forbes, H.-L. Liu, X. Dou, X. Xue, T. Li, and X. Luan. Latitudinal variation of lower thermosphere density: observations and modeling in press. J. Geophys. Res, doi:10.1029/2011JA017067.

Abtract: Observations from the Satellite Electrostatic Triaxial Accelerometer (SETA) satellite during September 1, 1983–October 31, 1983 are used to examine the variations of the equatorial density at around 210 km for the daytime (1030 LT) and midnight (2230 LT) sectors. It is found that both daytime and nighttime densities show an equatorial trough at the geographic equator and two crests aside the equatorial trough. The thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) reproduces the observed features seen in the SETA data. The simulation revealed that the observed two-hump structures at both daytime and midnight sectors are mainly associated with the tides excited locally at the middle lower thermosphere region, although they are modulated by the tides originating from the lower atmosphere.

(7)
Chang, L. C., S. E. Palo, and H.-L. Liu, 2011: Short-term variability in the migrating diurnal tide caused by interactions with the quasi 2 day wave. J. Geophys. Res., 116, D12112, doi:10.1029/2010JD014996.

Abtract: The migrating diurnal tide is one of the dominant dynamical features in the low latitudes of the Earth's mesosphere and lower thermosphere (MLT) region, representing the atmospheric response to the largest component of solar forcing. Ground-based observations of the tide have resolved short-term variations attributed to nonlinear interactions between the tide and planetary waves that are also in the region. Using the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM), we simulate a quasi 2-day wave (QTDW) event under late-January conditions. In this case, sideband sum and difference child waves are resolved, indicating that a nonlinear interaction is occurring between the QTDW and the tide. The migrating diurnal tide in the MLT displays local amplitude decreases of 20–40%, as well as a shortening of vertical wavelength by roughly 4 km. Examining the physical mechanisms driving the interaction, nonlinear advection is found to result in amplification of the tide in some regions and damping in others, manifesting as increased smoothing of the tidal structure when the QTDW is present in the MLT. Additionally, the QTDW also enhances the easterly summer mean wind jet that can also account for changes in tidal amplitude and vertical wavelength. We find that QTDW induced background atmosphere changes in TIME-GCM can drive tidal variability at levels greater than nonlinear advection, a possibility not previously considered.

(8)
Yamashita, C., H.-L. Liu, and X. Chu, 2010: Gravity wave variations during the 2009 stratospheric sudden warming as revealed by ECMWF-T799 and observations. Geophys. Res. Lett., 37, L22806, doi:10.1029/2010GL045437.

Abtract: ECMWF-T799 is used to study gravity wave variations during the 2009 stratospheric sudden warming (SSW) in the Arctic. The occurrence and magnitude of gravity waves correlate with the location and strength of the polar vortex that is strongly disturbed by planetary wave growth. This location dependence on planetary wave phase explains the observed gravity wave variability during SSWs. During the development and the onset of SSW, the zonal-mean gravity wave potential energy density (GW-Ep) increases on January 5 and 15, 22 in association with the growth of PW wavenumber 1 and wavenumber 2, respectively. As the initial prominent PW magnitude in the lower mesosphere progresses downward, GW-Ep enhancement also seems to show a corresponding descent from January 5, 22. GW-Ep peaks before the wind reversal occurrence and significantly weakens after the SSW. These variations are confirmed by COSMIC/GPS observations. Lidar data from Antarctica are also used to validate gravity waves as derived in ECMWF. Our research reveals that the gravity wave enhancements prior to the 2009 SSW are strongly tied to the increase of gravity wave excitation through residual forcings in the stratosphere. Decay of gravity waves after the 2009 SSW is most likely caused by the changes in gravity wave propagation and reduction of in-situ gravity wave source by unbalanced flow.

(9)
Yue, J., and H.-L. Liu, 2010: Fast meridional transport in the lower thermosphere by planetary-scale waves. J. Atmos. Solar Terr. Phys., 72, 1372–1378.

Abtract: Observations showed that the main engine water exhaust plumes from space shuttles released at 110 km altitude from Florida could be transported over thousands of kilometers northward or southward, reaching the Arctic after a day or so, and in one case Antarctica after three days. In this work, we study the meridional transport associated with the quasi-two-day wave (QTDW) andmigrating tides. Diagnostic calculations are performed to trace the particle trajectories using winds from the Thermosphere, Ionosphere, Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) simulations for January, when the amplitude of the QTDW usually peaks. The calculations demonstrate that the mean meridional circulation, a QTDW or a migrating tide cannot individually sustain planetary-scale meridional transport for one to three days, but the combined effects of a QTDW and a tide can. In particular, when the QTDW and the tides are scaled according to the observed amplitudes, particles released at 110 km and appropriate longitudes/local times can undergo transport fast enough to reach Antarctica within three days as observed. The magnitude and direction of the transport depend on the amplitudes and phases of the tides and the QTDW. These simulations thus suggest that the observed rapid planetary-scale meridional transport of the shuttle main engine plume can be driven by planetary waves and tides.

(10)
Yue, J., C.-Y. She, and H.-L. Liu, 2010: Large wind shears and stabilities in the mesopause region observed by Na wind-temperature lidar at midlatitude. J. Geophys. Res., 115, A10307, doi:10.1029/2009JA014864.

Abtract: Unexpected large horizontal winds and wind shears in the lower thermosphere have been observed by rocket soundings and lidars for decades. From 4 years of the Colorado State University sodium wind-temperature lidar data set (2002, 2005; total of 1600 nocturnal h), we observed an altitude distribution of high wind velocity and wind shears between 80 and 105 km, similar to the results of chemical release experiments. Our lidar data show conclusively that when the observed wind shears are plotted as a function of the squared Brunt-Vaisala frequency, N2, they are below the value corresponding to the Richardson number of 1/4, which is a necessary condition of the onset of dynamic instability. This suggests that large wind shears can be sustained in the region of high static stability, for example, in the lower thermosphere, where large wind shears are often observed by rocket sounding. The full-diurnal-cycle lidar data enable the extraction of tidal wave components with periods of 24, 12, 8, and 6 h, therefore allowing us to reveal the strong correlation of 60% between large wind shears (>50 m s, 1 km, 1) and tidal waves. The lidar-measured seasonal variation in N2 and tidal amplitudes in the mesosphere and lower thermosphere are found to be consistent with the difference in altitude distribution of strong wind shears between winter and summer.