HAO 2012 Profiles In Science: Dr. Hanli Liu

Contact:

303-494-1564
liuh@ucar.edu

Dr. Hanli Liu is a Senior Scientist 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.

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

Publications

(1) 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, 2012: Comparison of Diurnal Tide in Models and Ground-Based Observations during the 2005 Equinox CAWSES Tidal Campaign. J. Atmos. Solar Terr Phys., 78-79, 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.

Figure 1 caption: Model and observed diurnal tidal amplitudes as a function of latitude at 90km during September / October 2005. Meteor radar data denoted by asterisks, medium frequency radar sites denoted by diamonds, and lidar denoted by triangle. Model amplitudes computed at each model gridpoint and zonally averaged for each latitude circle, and denoted by lines as indicated.

(2) Yue, J., H.-L. Liu, and L. C. Chang, 2012: Numerical study of the quasi-two-day wave structures in the lower thermosphere. J. Geophys. Res., 117, D05111, doi:10.1029/2011JD016574.

Abtract: The zonal wave number 3 planetary wave with about a 2 day period is a recurrent wave feature in the mesosphere and lower thermosphere (MLT). The quasi 2 day wave (QTDW) exhibits strong seasonal variability with peak amplitudes after summer solstice. In late January and early February, satellites also discovered two strong enhancements of the QTDW in meridional wind, one peak at summer midlatitudes near 90 km and the other in the tropical lower thermosphere. For the first time, 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 and explained by the combined effect of baroclinic-barotropic instability and Rossby normal mode. Baroclinic-barotropic instability is capable of amplifying the QTDW, manifesting as Eliassen-Palm (EP) flux divergence in the summer mesosphere. Without the direct contribution from baroclinic-barotropic instability, the simulated QTDW response in a 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 an internal wave in the regions of large refractive index. As the wave amplitude growth ceases near the mesopause, where the zonal wind reverses direction, the QTDW reaches its maximum amplitude, displaying an enhanced meridional component in the tropical lower thermosphere. Several new aspects on the QTDWs in the MLT were also revealed. Compared with 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.

Figure 2 caption: Amplitudes of quasi-two-day wave in meridional wind with different wave periods prescribed at the lower boundary: (a) 44 h, (b) 52 h, and (c) 56 h under the same background atmosphere conditions.

(3) Xue, X., H.-L. Liu, and X. Dou< 2012: Parameterization of inertial gravity waves and generation of quasi-bienniel oscillation. J. Geophys. Res., 117, D06103, doi:10.1029/2011JD016778.

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 the inertia-gravity waves (IGW). We perform WACCM simulations 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 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. The 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 (GCMs).

Figure 3 caption: Time-height cross section of the monthly mean zonal-mean zonal winds and the inertial gravity wave forcings averaged from 2.5_N to 2.5_S for ten year run of WACCM with the parameterized gravity wave forcing. Winds are plotted in intervals of 10 m/s. Red and blue colors correspond to eastward and westward wave forcing, respectively.

(4) Tan, B., X. Chu, H.-L. Liu, C. Yamashita, and J. M. Russell III, 2012: Zonal-mean global teleconnection from 15 to 110 km derived from SABER and WACCM.J. Geophys. Res., 117, D10106, doi:10.1029/2011JD16750.

Abtract: We derive the correlation patterns over the global latitudes and from the stratosphere to lower thermosphere (broadly referred to as teleconnection) using temperature data measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) from 2002 to 2010, and using 54 years of simulations of temperatures and winds by the Whole Atmosphere Community Climate Model (WACCM). We also analyze the possible mechanisms of teleconnection by investigating the correlations between the temperature and residual circulation. The correlation patterns show that teleconnection exists globally over the equatorial, mid-and high-latitudes, and temperature anomalies correspond well to the anomalies of the residual circulations through adiabatic heating/cooling. A main new finding of this study is that the teleconnection extends well into the lower thermosphere, the thermospheric anomalies are consistent with the corresponding changes of the winter-to-summer lower-thermospheric branch of the residual circulation, and the winter stratosphere perturbations influence the thermosphere globally. Using a reference point chosen in the northern winter stratosphere, we find that the teleconnection structures for time periods with and without Sudden Stratospheric Warmings (SSWs) display similar patterns in SABER, and teleconnection patterns in WACCM are nearly identical for days with major SSWs, minor SSWs and without SSWs. WACCM results show strong inter-annual and intra-annual altitude variations of the teleconnection patterns in the southern polar region but stable altitudes of correlation regions in the equatorial and northern latitudes. The altitude variations are likely responsible for the weak correlations poleward of 60 degrees S when multiyear or multimonth data are used.

Figure 4 caption: Correlation patterns between the deseasonalized SABER temperature series at a reference point (10 hPa, 76_N) and at all other latitudes and altitudes for days (left) with SSWs and (right) without SSWs. The circle with a cross is the reference point used for the correlation calculations. White solid lines denote the 95% significance level.

(5) Lu, X., H.-L. Liu, A. Z. Liu, J. Yue, J. M. McInerney, and Z. H. Li, 2012: Momentum budget of the migrating diurnal tide in the Whole Atmosphere Community Climate Model. J. Geophys. Res., 117, D07112, doi:10.1029/2011JD017089.

Abtract: The momentum budget of the migrating diurnal tide (DW1) at the vernal equinox is studied using the Whole Atmosphere Community Climate Model, version 4 (WACCM4). Classical tidal theory provides an appropriate first-order prediction of the DW1 structure, while gravity wave (GW) forcing and advection are the two most dominant terms in the momentum equation that account for the discrepancies between classical tidal theory and the calculation based on the full primitive equations. It differs from the conclusion by McLandress (2002a) that the parameterized GW effect is substantially weaker than advection terms based on the Canadian Middle Atmosphere Model (CMAM). In the region where DW1 maintains a large amplitude, GW forcing in the wave breaking region always damps DW1 and advances its phase. The linear advection largely determined by the latitudinal shear of the zonal mean zonal wind makes a dominant contribution to the phase change of DW1 in the zonal wind compared to the GW forcing and nonlinear advection. However, nonlinear advection is more important than GW forcing and linear advection in modulating the amplitude and phase of DW1 in the meridional wind. The DW1 amplitudes in temperature and winds are smaller than the TIMED observations, suggesting that GW forcing is overestimated in the WACCM4 and results in a large damping of DW1.

Figure 5 caption: Time tendency amplitudes in the DW1 component of (a) total advection forcing, (b) total GWforcing and (c) the sum of them in the zonal momentum from WACCM simulation. The unit is m/s/day.

(6) Liu, H.-L., 2012: WACCM-X Simulation of Tidal and Planetary Wave Variability in the Upper Atmosphere, AGU Monograph on Modeling the Ionosphere-Thermosphere System. Ed. J. Huba, R. Schunk, and G. Khazanov, in press.

Abtract: A 20-year climate simulation using CESM1/WACCM-X has been made under constant solar and low geomagnetic conditions, and the simulation is analyzed to study the tidal variability in relation to the variability of mean state and planetary waves. On inter-annual scales, the migrating diurnal and semidiurnal tides (DW1 and SW2) and the nonmigrating diurnal eastward propagating wave 3 component (DE3) in the MLT are modulated by the quasi-biennial oscillations (QBO). Correlation analysis are performed between de-seasonalized tidal wave amplitudes with winter stratospheric state anomalies for solstitial periods. The correlation between DW1 amplitude at mid and low latitudes and the winter polar stratospheric temperature anomalies is negative in the winter hemisphere, and alternates signs over altitudes in the summer hemisphere. SW2 shows a significant positive correlation with the winter polar stratospheric temperature anomalies in the summer stratopause, low and mid-latitudes in the mesosphere, and lower thermosphere. The correlation alternates signs with altitudes at mid to high latitudes in the winter hemisphere. The nonmigrating semidiural westward propagating wave 1 (SW1) in the summer mesosphere and lower thermosphere (MLT) region correlates positively with the planetary wave 1 in the winter stratosphere. DE3 in the equatorial MLT region, where it peaks, does not show any significant correlation with the winter stratosphere anomalies. The short-term variability of these tidal components has time scales of several days, much shorter than the typical time scales of stratospheric planetary wave variability (10–20 days). The magnitude of the day-to-day tidal variability is significant and is persistent throughout the year.

Figure 6 caption: Meridional wind of migrating diurnal (upper panel) and semidiurnal (lower panel) at 20N and 52N, respectively, both at 10-4hPa, from (a and d) first January, (b and e) first year, and (c and f) all 20 years of WACCM-X simulations. In (a-b) and (d-e), the solid lines are daily values, and the dotted lines are climatological values from the 20 years of simulations. In (c and f), the solid lines are monthly mean values and the dashed lines are daily values; the dark dashed lines are the equatorial zonal mean zonal wind at 30hPa, shifted by 25 and 35m/s respectively (0 wind denoted by the thin horizontal lines), and scales reduced by 5 fold. The QBO phase can be read from the equatorial wind.