Jielun Sun

Scientist III
TIIMES - MMM
BEACHON - BGS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: FL3 - 3052
Telephone: 303-497-8994
Email: jsun@ucar.edu
Home Page

Project Summary:

Click on picture to view the entire figure.

CHATS Setup

Additional CHATS pictures by Sun

I have been working on CO2/trace-gas transport over complex terrain for several years. It involves field work (CME-04, ACME-04, and Niwot-07), and their data analysis. I have also involved various planning work related to TIIMES, such as Fraser Valley Experiment (although not funded yet) and BEACHON.  During the fiscal year of 2007, I participated in CHATS, which is supported by BEACHON, and a small field experiment, Niwot-07, which involves testing new instruments over Como Creek at the Niwot Ridge site. In addition, I also focused on nighttime turbulence transport over a flat land by analyzing the CASES99 dataset, which sets an initial state for understanding trace gas turbulent transport within and over canopies over complex terrain. 

Discoveries, developments, interesting results, work done this fiscal year:

Finally the first part of my work on CO2/trace-gas transport over complex terrain was published in two parts. One paper, which mainly focuses on CO2 budget over the Niwot Ridge site, appears in Agricultural and Forrest Meteorology, and another paper, which focuses on how to analyze the CO2 budget over complex terrain, appears in Boundary-Layer Meteorology.

Click on picture to view the entire figure.

Figure 1: Two morning CO2 profiles from ACME-04 and the map which shows where the two soundings were taken. The blue one was from the area surrounded by mountains and the red one is from the Front Range.

I have been working on the data analysis from CME-04 and ACME-04. Based on ACME-04, I found that morning CO2 mixing is very different in the area surrounded by mountains from flat lands. Over the Front Range, CO2 is well mixed up at about 8 am, which is similar to turbulent mixing over flat lands.  However, over the area surrounded by mountains, I found that CO2 concentration still decreases with height even around noon, which is its nighttime character (Figure 1 to the left).

Currently all the boundary layer numerical models do not have adequate physics in dealing with topography and surface heterogeneity. The result has strong implication on all the efforts to obtain regional CO2 budget over complex terrain. In other words, if we treat boundary layer mixing over complex terrain as if it were over flat lands, we would expect serious deviations of numerical models from the reality.

In addition, as part of my work related to the nocturnal stable boundary layer, I also analyzed temperature and momentum transfer at night by using the CASES99 dataset. I found that the nighttime turbulence transport, including turbulent heat and trace gas transport, is dominated by shear generated turbulence. In other words, turbulence transport depends on momentum fluxes. Monin-Obuhkov (M-O) similarity theory, which is the only theory that all numerical models rely on, does not work close to the ground for all fluxes including momentum, heat and trace gas fluxes. Close to the ground, the vertical temperature gradient is constantly influenced by cold drainage flow even over reasonably flat areas. As a result, the heat flux does not proportional to the vertical temperature gradient, but to the shear generated turbulence. Since temperature is an active scalar, and trace gasses such as CO2 are passive scalars, we would expect temperature plays a more active role in turbulence generation than trace gases do. My results demonstrate that even temperature plays a minor role in damping turbulence and the key is whether there is shear to generate turbulence. This result has significant impacts on numerical modeling of trace gas transports since all numerical models assume that the turbulent mixing of trace gases follows M-O similarity theory as temperature does.

In addition, I also found that the dependence of momentum flux on shear close to the ground is different from that in the surface layer where M-O is valid. The deviation is due to larger dissipations close to the ground. Therefore, the existing momentum flux parameterization is wrong, which is significant since the momentum flux is the driving force for other trace gas transport either active one such as temperature or passive one such as CO2.

Future plan:

I will continue to work on CME-04 and ACME-04 data analysis to learn CO2/H2O transport over complex terrain on a relatively large scale and within canopy. In addition, I will investigate how water body affects CO2 transport at night by analyzing Niwot-07 data. Based on my results on CASES99, I will focus on trace gas transport over and within canopies by analyzing the CHATS dataset (hopefully the CHATS dataset will come out in FY08).  I will try to understand how canopies, similar to the ground, impinge large eddies in momentum transfer, which can be the driving force in trace gas turbulent mixing within and over canopies. In addition, I will keep involved in BEACHON activities to help understand various land-surface transport processes.

Community Service:

• Associate Editor - Journal Applied Meteorology
• Editor - Boundary-Layer Meteorology

Presentations:

• Carbon in the mountain, Boulder USA, June 2007

TIIMES External Collaborators:

Dean Anderson, United States Geological Survey (USGS)
Stephan DeWekker, University of Virginia
Larry Mahrt, Oregon State University
Russell Monson, University of Colorado

Publications:

Lenschow, D. H., J. Sun, 2007: The spectral composition of fluxes and variances over land and sea out to the mesoscale. Bound.-Layer Meteor., 125, 63-84, doi: 10.1007/s10546-007-9191-8.

Banta, R. M., L. Mahrt, D. Vickers, J. Sun, B. B. Balsley, Y. Pichugina, E. J. Williams, 2007: The very stable boundary layer on nights with weak low-level jets. J. Atmos. Sci., 64, 3068-3090, doi: 10.1175/JAS4002.1.

Sun, J., 2007: Tilt corrections over complex terrain and its implication for CO2 transport. Bound.-Layer Meteor., 124, 143-159, doi: 10.1007/s10546-007-9186-5.

Sun, J., S. P. Burns, A. C. Delaney, S. P. Oncley, A. A. Turnipseed, B. B. Stephens, D. H. Lenschow, M. A. LeMone, R. K. Monson, D. E. Anderson, 2007: CO2 Transport over Complex Terrain. Agric. For. Meteorol., 145, 1-21, doi: 10.1016/j.agrformet.2007.02.007.

Edson, J., T. Crawford, J. Crescenti, T. Farrar, J. French, N. Frew, G. Gerbi, C. Helmis, T. Hristov, D. Khelif, A. Jessup, H. Jonsson, M. Li, L. Mahrt, W. McGllis, A. Plueddmann, L. Shen, E. Skyllingstad, T. Stanton, P. Sullivan, J. Sun, J. Trowbridge, D. Vickers, S. Wang, Q. Wang, R. Weller, J. Wilkin, D. Yue, C. Zappa, 2007: The coupled boundary layers and air-sea transfer experiment in low winds (CBLAST-Low). Bull. Amer. Meteor. Soc., 88, 341-356, doi: 10.1175/BAMS-88-3-341.

Schaeffer, S., S. P. Burns, D. E. Anderson, J. Sun, C. Yi, D. R. Bowling, 2006: Environmental controls on the delta C13 of forest respired CO2 across a vertical canopy profile in a subalpine coniferous forest. 2006 Fall Mtg., San Francisco, CA, US, AGU.