Changhai Liu

Project Scientist
TIIMES - MMM
BEACHON & WCAS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: FL3 - 2027
Telephone: 303-497-8170
Email: chliu@ucar.edu
Home Page

Project Summary:

Brief History of My TIIMES Research

I have been involved in the NCAR Water Cycle Program for a few years and in BEACHON Program since this fiscal year. In the early time of my TIIMES's appointment, my research focused on simulations of US warm season precipitation sequences using both explicit and parameterized approaches. Later, I concentrated on the development and testing of the mesoscale parameterization representing the missing or under-resolved stratiform heating/cooling in coarse grid resolution models as well as on observational studies of precipitation episodes and diurnal variations over the Bay of Bengal and Tibetan Plateau using the TRMM rainfall data. More recently, my efforts concentrate on the impacts of cloud microphysics processes, land surface treatment, and aerosol properties on warm-season organized convection and simulations of mountain-plains solenoidal circulations that often initiate the summertime propagating organized convection east of the Rockies.

Work Done in FY 2007

Collaborators: Mitch Moncrieff, Kyoko Ikeda, Roy Rasmussen, Xianfan Ma, Aijuan Bai, John Tuttle

During the past year our research funded by Tiimes Water Cycle and BEACHON Programs involved the following issues.

A numerical modeling study of thermally and mechanically driven diurnal flows in the lee of the Rockies was conducted in an idealized framework, namely, driving a nonhydrostatic model using the averaged diurnal potential temperature obtained from a week-long convection-permitting simulation with MM5. A reasonable mountain-plains solenoidal circulation is produced in response to the daily elevated heating cycle associated with the Rocky Mountains. In particular, the daytime (nighttime) mesoscale upslope (downslope) wind and resultant upward (downward) motion over the mountain peak and around the eastern edge are quite realistic. Furthermore, the roughly 400-km wide area of descent east of the Rockies during the afternoon-evening hours is consistent with the daytime suppressed convective region documented from Carbone et al.'s radar observations. The upslope/downslope wind strength is significantly affected by background flows, but the upward/downward motion pattern is largely insensitive. [see slide one] (Liu & Moncrieff)

Click on picture to view the entire figure.

Slide 2: Left panel: The 7-day composite diurnal Hovmoller diagrams of meridionally-averaged surface rainfall rate. (a) Radar observations, and (b)-(d) simulations using Noah land-surface model, five-layer soil model, and Noah land-surface model without precipitation feedback, respectively. Right panels: Evolution of (a) domain-averaged temperature and (b) water vapor mixing ratio at the lowest model level (~25 m above the ground) for simulations using Noah land-surface model (solid), five-layer soil model (dashed), and Noah land-surface model without precipitation feedback (dotted), respectively.

We continued the study of the impact of land surface treatment on warm-season precipitation simulations at convection-permitting grid resolution. Two surface schemes are tested: Dudhia's five-layer soil model (FLSM) and the Noah land-surface model (NLSM). The experimentation case involves a one-week episode of active summertime convection over the central United States. The overall precipitation features, such as the diurnal regeneration of zonally-propagating rainfall episodes and the spatial distribution of accumulative rainfall, are adequately replicated by the two parameterizations. In comparison, NLSM produces roughly 12% more and broader rainfall than FLSM. This differential rainfall amount is consistent with the differential surface moisture fluxes between the two schemes, whereas the precipitation feedback plays a negligible role. It is also found that FLSM generates comparatively stronger sensible heat transports from the land surface and thus a warmer temperature near the surface. [see slide two] (Liu & Moncrieff)

Click on picture to view the entire figure.

Slide3: Left panel compares the total condensate at the mature stage of simulated squall lines; Right panels compare the accumulated rainfall and rainfall rate during the 10-hour simulations.

We continued the examination of the effects of cloud microphysics parameterizations on squall-type organized convection simulations in an idelaized framework. Three microphysics parameterization schemes are tested: Purdue Lin et al. scheme, WSM6 scheme, and Thompson et al. scheme. In general, mesoscale organization and structure are insensitive to microphysical parameterizations. But moderatet-to-strong sensitivity to cloud microphysics occurs in rainfall amount, rainfall spectrum, upper-level cloud fraction, and heating distributions. Currently we are making detailed comparisons of the individual microphysics processes among the three schemes. [see slide three] (Ikeda, Liu, Rasmussen, Moncrieff)

We performed idealized simulations of summertime continental-scale convective organization over the continental US. The WRF model is driven using diurnally-varying forcings averaged over a multi-day period to isolate the impact of elevated heating on convective development from synoptic forcings. The results show that the observed daily-repeating generation of convection lee of the Rockies is well replicated. However, the simulated convective system is less organized and persistent compared to observations, and this is likely associated with the coarse grid resolution used in our explicit simulations. (Ikeda, Liu, Moncrieff, Rasmussen)

Click on picture to view the entire figure.

Slide4: (a) Zonally-averaged rain rate Hovmoller (latitude-time) diagram and (b) meridonally-averaged Hovmoller (longitude-time) diagram for 3-23 June 2003. Majority of the warm-season rainfall episodes over the Bay of Bengal traslate southward and do not appear to have a steering level, unlike those documented in other regions.

We continued and completed the observational investigation of precipitation episodes over the Bay of Bengal and adjacent coastal region using the TRMM Real Time Multi-Satellite Precipitation Analysis products for three warm seasons. Reduced dimension analysis reveals frequent traveling precipitation episodes having lifetimes greatly exceeding those of individual convective systems. The majority of the episodes translate southward and many do not appear to have a steering level, unlike those previously documented over midlatitude and tropical continents which have a steering level. The same rainfall dataset was used to investigate the diurnal variation patterns of summertime precipitation over the Tibetan Plateau and nearby areas. Both precipitation amount and frequency exhibit pronounced daily variability with the strongest signal over the central Plateau and Indian Peninsula. A late-afternoon-evening maximum and a morning minimum are dominant, consistent with the diurnal phasing documented in other continental regions. A striking exception is the nocturnal maximum around the Plateau periphery. Additionally, coherent diurnal patterns associated with eastward-propagating convection are present at leeside of the Plateau and exhibit a progressively delayed phase. [see slide 4] (Liu, Bai, Moncrieff, Tuttle)

Click on picture to view the entire figure.

Slide 5: Evolution of domain-averaged accumulated rainfall for cloud-resolving simulations of a midlatitude continental mesoscale convective system (MCS) observed in Beijing on 23 August 2001 under three scenarios of aerosol concentration, showing that increased aerosol concentration delays and reduces surface precipitation.

We performed a set of cloud-resolving simulations of three midlatitude and tropical continental mesoscale convective systems (MCSs) under various scenarios of aerosol concentration (i.e., referred to as PRISTINE or MARITIME, CONTINENTAL, and POLLUTED CONTINENTAL). Preliminary analysis illustrates that the aerosol concentration has significant influence on cloud properties (i.e., cloud water and ice concentrations, cloud fraction, liquid and ice water paths, and cloud optical depth) and thus cloud-radiation interactions, but the evolution and overall structure of mesoscale organized convection has little dependence on the aerosol property. Moreover, the effect of aerosol concentration on the accumulative rainfall during the lifetime of an MCS is case-dependent, even though increased aerosol concentration always delays the development of deep convective cells and thus surface precipitation at the initial phase of organized convection. [see slide five] (Liu, Ma, Ikeda, Rasmussen)

Plans for FY2008

In the coming year we will concentrate on the following specific issues:

1. High resolution regional climate simulations of snowpack, evapo-transpiration, and runoff in the western states;

2. Further refining our mesoscale parameterization and testing it in Community Atmospheric Model (CAM);

3. Evaluation and improvement of momentum transport parameterizations in CAM using the cloud-resolving simulations of convective cloud systems during the 4-month intensive observation period of TOGA COARE (in collaboration with CGD scientists), and

4. Multi-scale evaluation and improvement of PBL and cumulus parameterizations in modeling the diurnal variation of summertime precipitation.

Community Service:

• Advisor on Graduate Research: Aijuan Bai, , Institute of Earth Environment, Xian, CHN
• Advisor on Graduate Research: Xianfang Ma, , Institute of Earth Environment, Xian, CHN

Presentations:

• Warm-Season Rainfall: Observations and Simulations, Boulder USA, December 2006

TIIMES External Collaborators:

Chunguang Cui, Wuhan Heavy Rain Institute
Danhong Fu, Institute of Atmospheric Physics
Xueliang Guo, Institute of Atmospheric Physics
Xiaodong Liu, Institute of Earth Environment
Zaitao Pan, Saint Louis University
Lulin Xue, Saint Louis University

Publications:

Das, S., R. Ashrit, M. W. Moncrieff, M. Dasgupta, J. Dudhia, C. Liu, S. R. Kalsi, 2007: Simulation of intense organized convective precipitation observed during the Arabian Sea Monsoon Experiment (ARMEX). J. Geophys. Res. - Atmos., 112, doi: 10.1029/2006JD007627. (In Press)

Liu, C.-H., M. W. Moncrieff, 2007: Comparison of two land surface schemes in week-long cloud-system-resolving simulation of warm season precipitation. J. Appl. Meteor. Climat.. (Submitted)

Liu, C., M. W. Moncrieff, 2007: Sensitivity of cloud-resolving simulations of warm-season convection to cloud microphysics parameterizations. Mon. Wea. Rev., 135, 2854-2868, doi: 10.1175/MWR3437.1.

Bai, A.-J., C.-H. Liu, X.-D. Liu, 2007: The diurnal variation of warm-season precipitation over the Tibetan Plateau and its neighboring regions. J. Geophys. Res.. (In Press)

Liu, C.-H., M. W. Moncrieff, J. D. Tuttle, 2007: Propagating rainfall episodes over the Bay of Bengal. Geophys. Res. Lett.. (Submitted)

Moncrieff, M. W., and C.-H. Liu, 2006: Representing convective organization in prediction models by a hybrid strategy. J. Atmos. Sci., 63, 3404-3420.