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Chengji Liu

PhD Candidate, Barnes Research Group
Email: cjliu@atmos.colostate.edu
Curriculum Vitae



My main research interest is the large-scale dynamics regarding the transport and mixing of constituents important for climate (e.g. moisture, ozone). The focus of my PhD work is using Rossby wave breaking to explain how the strength and spatial distribution of transport and mixing may respond to both internal climate variability and future climate change. I examine three factors that determine the contribution of Rossby wave breaking to the global transport and mixing: the frequency of occurrence, the type of wave breaking, and the tropopuase structure related to wave breaking.

The data I use includes reanalysis, satellite observations, output from idealized general circulation models, and chemical transport models. To take full advantage of the data, I implement and develop various diagnostic tools, such as feature tracking algorithms for wave breaking and extratropical cyclones, as well as mixing quantification framework in tracer coordinates. They all take a Lagrangian perspective while dealing with data in Eulerian form.

Extreme moisture transport into the Arctic

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Mixing ratio of water vapor (shading), and horizontal wind (arrows) on
700 hPa for (a) an anticyclonic wave breaking, and (b) a cyclonic
wave breaking

Atmospheric river-like moisture transport are not only important for extreme weather, but also essential for climate, especially at the high latitudes. Although occurring infreqeuntly, they account for a bulk of total transient moisture transport into the Arctic. Our study documented the dominant role Rossby wave breaking plays in driving these events. The frequency of Rossby wave breaking is in turn linked to the jet positions and hence climate variability involving jet shift such as El-Nino and southern oscillation (ENSO) and the North Atlantic Oscillation (NAO). It is through such modulation on wave breaking frequency that tropical and midlatitude climate variability influences the Arctic moisture and climate.

Related publication:

Liu, Chengji and Barnes, Elizabeth A., 2015: Extreme moisture transport into the Arctic linked to Rossby wave breaking. Journal of Geophysical Research, doi:10.1002/2014JD022796.

Isentropic mixing modulated by jet variability

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Mixing strength associated with AWB/LC1 and CWB/LC2 in both idealized
wave breaking simulations and a climate simulation

Besides the frequency of Rossby wave breaking, the flavor/type also matters. There are two distinct types of wave breaking -- anticyclonic and cyclonic -- exhibiting opposite overturning direction. Using a Lagrangian quantification framework, we found a robust asymmetry in mixing strength between these two types of wave breaking in both idealized eddy lifecyle simulation and a long climate simulation. Cyclonic wave breaking is generally more efficient in isentropic mixing than anticyclonic wave breaking. Since both types of wave breaking have robust but distinct relationships with the jet position, such asymmetry translates into a change in total isentropic mixing strength when the jet shifts. The results suggest a decrease in isentropic mixing strength for a more poleward jet position in future climate.

Related publication:

Liu, Chengji and Elizabeth A. Barnes, 2017: Quantifying Isentropic Mixing Linked to Rossby Wave Breaking in a Modified Lagrangian Coordinate. submitted to Journal of the Atmospheric Sciences.

Synoptic formation of double tropopauses

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Composite variables for anticyclonic wave breaking (AWB) in the left
column and cyclonic wave breaking (CWB) in the right column.

Double tropopauses are ubiquitous in the midlatitude winter hemisphere and represent the vertical stacking of two stable tropopause layers separated by a less stable layer. we demonstrate that they often occur during Rossby wave breaking and act to increase the stratosphere-to-troposphere exchange of mass. We further investigate the adiabatic formation of double tropopauses and propose two mechanisms by which they can occur -- differential advection and/or the destabilization of thermal stratification.

Related publication:

Liu, Chengji and Barnes, Elizabeth A., 2017: Synoptic formation of double tropopauses submitted to Journal of Geophysical Research