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- Table of Contents
- Strategic Goals: Science, Facilities & Technology
- 1. Exploring atmospheric, Earth system, and solar processes, variability, and change
- 2. Investigating the interaction of the atmosphere, the broader Earth system, and human society
- 3. Improving prediction of weather, climate, and other atmospheric phenomena
- 4. Developing community models
- 5. Enabling innovative field experiments and measurement campaigns
- 6. Developing new instrumentation
- Research Catalog
Changhai Liu
General Information
|
MMM - TIIMES
Project Scientist
BEACHON & WCAS
Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: FL3 - 2027
Telephone: 303-497-8170
Email: chliu@ucar.edu
Home Page - Vita
Research Focus FY08:
Colorado Headwaters Program
(Liu, Kyoko, Rasmussen, Moncrieff ...)
The Colorado Headwaters Program is a key project of NCAR's Water System Program in this fiscal year. Its major objective is to assess the projected Upper Colorado Snowpack and Runoff by global climate models using a very high resolution regional climate model. We started from the present-day cold season simulations in this region to evaluate the sensitivity of the simulated snowfall and snowpack to both the horizontal and vertical grid spacings as well as the various physical parameterizations. We have performed a series of 2~30-km resolution experiments over two multi-day periods (i.e., November 19 -- December 8, 2002; February 1--16, 2008) with the WRF model. North American Regional Reanalysis (NARR) data are used to provide the initial and boundary conditions in our simulations. The Snow Telemetry network (SNOTEL) and PRISM observations are used to evaluate the simulated snowfall. The preliminary analysis indicates that 1) the high-resolution simulations with 2~4-km grid spacing can well capture the heavy snowfall episodes during the two periods; 2) the simulated snowfall has little dependence on the choice of the PBL and land-surface schemes, but shows considerable sensitivity to the choice of microphysics parameterizations; and 3) the model performance gradually degrades when the grid spacing is coarser and coarser.
Cloud-resolving simulations of convective cloud systems in TOGA COARE
(C.-H. Liu)
The WRF model was configured to run the three-dimensional cloud-resolving simulations of convective cloud systems during the 4-month intensive observing period of Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). We started with a small computational domain which was only 64 km by 64 km so that our simulation results can be compared with previous CRM simulations which used the same domain size. Preliminary evaluation showed that the model well replicated the observed precipitation evolution. Our CGD collaborators will use the model data for momentum transport parameterization studies. We are going to repeat the simulation with a domain large enough to accommodate mesoscale convective systems.
Evaluation and improvement of YSU and MYJ PBL schemes in modeling the diurnal variation of summertime precipitation
(Y.-H. Yang, C.-H. Liu, J. Dudhia, M. Moncrieff, F. Chen)
We are performing hierarchical modeling of diurnal evolution of PBL and convective development with the WRF model. The numerical model is forced by specified diurnally-varying surface fluxes derived from an idealization of the observations made during the Tropical Rainfall Measuring Mission, Large Scale Biosphere-Atmosphere (TRMM-LBA) mission. The unique aspects in our approach are the employment of large-eddy simulations as a benchmark and the highly idealized experimental design that is much easier to isolate the errors associated with the tested physical parameterization than the real-data simulation approach. Three sets of diurnal three-dimensional simulations were completed, including 1) 50-m grid-spacing large-eddy simulations in which the PBL scheme is not required, 2) 1~4-km-resolution cloud-resolving simulations with the YSU scheme, and 3) 1~4-km-resolution cloud-resolving simulations with the MYJ scheme. The two PBL schemes are evaluated by comparing large-eddy simulation results against cloud-resolving simulation results. Preliminary results showed that the YSU (MYJ) scheme tends to overpredict (underpredict) the vertical mixing and thus the PBL development. Detailed evaluation is still under way.
Diurnal variations of summertime precipitation over the Tibetan Plateau in relation to orographically-induced regional circulations
(X.-D. Liu, A.-J. Bai, C.-H. Liu)
The diurnal variation patterns of summertime precipitation over the Tibetan Plateau were first investigated using the TRMM multi-satellite precipitation analysis product for five summer seasons (i.e., June through August for 2002-2006). Both hourly precipitation amount and frequency exhibit pronounced daily variability with the strongest signal over the central Plateau. Overall, a late-afternoon-evening maximum and a morning minimum are dominant, similar to the diurnal phasing documented in other continental regions. An exception is the prevalent nocturnal maximum around the Plateau periphery.
Using six-hourly NCEP FNL data, we then examined the diurnal variability in the atmospheric circulation and thermodynamics in this region. The results show that the Plateau heats (cools) the overlying atmosphere during daytime (nighttime) more than the surrounding areas, and as a consequence, a relatively stronger confluent circulation in this region occurs during daytime than during nighttime, consistent with the diurnal rainfall cycles therein. This study further demonstrates the importance of the Tibetan Plateau in regulating regional circulation and precipitation.
Community Service FY08:
- Graduate Advisor: Aijuan Bai, Institute of Earth Environment, Xian, China
- Graduate Advisor: Xianfang Ma, Institute of Earth Environment, Xian, China
Scientific Talks FY08:
- Preliminary Results of Multi-day Snowfall Simulations over the Colorado Headwaters Region (Boulder, CO, March 2008)
- Assessment of Snowfall, Snowpack and Runoff over Colorado's Headwater Region Using a High Resolution Regional Climate Model (Xian, China, August 2008)
Publications FY08 (abstracts):
Ikeda, K., R. M. Rasmussen, C.-H. Liu, G. Thompson, L. Xue, 2008: Investigation of the dependence of squall line structure and dynamics on microphysical parameterization. 15th Intl. Conf. on Clouds and Precipitation, Cancun, MX, International Association of Meteorology and Atmospheric Science.
Liu, C.-H., Q. Xiao, B. Wang, 2008: An ensemble-based four-dimensional variational data assimilation scheme: Part I: Technical formulation and preliminary test. Mon. Wea. Rev., 136, 3363-3373, doi: 10.1175/2008MWR2312.1.
Liu, C.-H., M. Moncrieff, 2008: Explicitly simulated tropical convection over idealized warm pools. J. Geophys. Res.. (Submitted)
Liu, C.-H., M. W. Moncrieff, J. D. Tuttle, 2008: A note on propagating rainfall episodes over the Bay of Bengal. Quart. J. Roy. Meteor. Soc., 134, 787-792.
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, D20117, doi: 10.1029/2006JD007627.
Bai, A.-J., C.-H. Liu, and X.-D. Liu, 2008: The diurnal variation of warm-season precipitation over the Tibetan Plateau and its neighboring regions revealed by TRMM Multi-satellite Precipitation Analysis. J. Geophys. (Chinese), submitted.
Liu, X.-D., A.-J. Bai, and C.-H. Liu, 2008: Diurnal variations of summertime precipitation over the Tibetan Plateau and their relationship with orographically-induced atmospheric circulations. Quart. Roy. Meteor. Soc., submitted.
Ma, X.-F., C.-H. Liu, X.-D. Liu, R. Rasmussen, D.-H. Fu, and U. Blahak, 2008: A numerical study of aerosol concentration on a midlatitude mesoscale convective system. J. Applied Meteorology (Chinese). in press.
Fu, D.-H., X.-L. Guo, and C.-H. Liu, 2008: Characteristics of precipitation and cloud microphysics of monsoon convective systems over the South China Sea. J. Geophys Res., submitted.