About this issues, I suggest you to look at my review “Wang, K., and R. E. Dickinson (2012), A review of global terrestrial evapotranspiration: Observation, modeling, climatology, and climatic variability, Rev. Geophys., 50, RG2005, doi:10.1029/2011RG000373.” In this review, I explain the reasons for energy imbalance and how correct this issue.

Thanks, Kaicun. I have read this review paper already. It was a nice work on ET. However, I want to quantify the advection effects and I want to know how advection effects on the surface energy balance.

Thanks Matthew. Sounds very interesting. If your papers are published, please let me know. Most research works assumed advection is very small and can be neglected and all the uncertainties are attributed to the measurements of G. I wish I could find EC observations on the water surface where G may be accurate and representative.

Was the heat exchange between soils and the atmosphere observed and considered in the balance? You may compare the data from different periods with different advection conditions to roughly estimate the advection effects.

Hi all

That's a very interesting and discussed point in EC community. There are different reasons why the balance closure is rarely observed with EC technique: advection is one of them, but recently Nakai&Shimoyama developed a new correction for the angle of attack error due to the sonic anemometer geometry (see attachment): heat fuxes can be underestimated up to 14% beacause of this kind of error - so if we could correct it, the closure imbalance in most cases would be solved. They found a correction only for Gill anemometer: that's the big limit. But I think it's an important step for the future.

Hope this helps

Simone

Thanks, Simone. This paper is very helpful.

Though the ADVEX experiment was mainly about advection of CO2, there are some papers from Uta Moderow et al. that discuss also the advection of sensible heat:

Bound. Layer Meteorol. (2007) 123:99-120

Theor. Appl. Climatol. (2009) 98:397-412

Agr. For. Meteorol. (2011) 692-708

Did you know this paper by Mauder, 2008? It's a little long, but very interesting analysis of large-scale eddies and their influence on the balance closure.

Greetings

Simone

Thanks very much, Simone.

Yes, advection may play a role in this problem, but remember that advection may have either sign and, therefore, it´s neglection could cause either underestimation of overestimation of the surface fluxes. However, the vast majority of observations show that the EC fluxes underestimate the net radiation, so there must be a different cause.

In my opinion, the most important cause for the problem is not properly accounting forthe role of the low-frequency exchange. Many papers have addressed the issue (Sakai and Fitzjarrald, 2001- J. Appl. Meteor. 40, 2178-2191 being one of them), but a solution to it is still not clear. The problem is that if you do your EC over longer time windows to acount for those fluxes you may violate stationarity issues and compromise the whole methodology.

Thanks, Otavio Acevedo. YES,The low-frequency exchange may be an important reason for this problem. Once a time, I try to find EC observations over the lake or over the sea surface. The water surface is more homogeneous than the land surface, and the uncertainties related to G may be lowered. However, Brutsaert(1982) pointed out the atmosphere boundary layer is almost never uniform, it is continually responding to weather patterns, involving condensation and unsteady flows, even over the ocean. I think the flux observed at the observation height may not fully reflect the fluxed from the underlying surface if the boundary layer is not uniform. I wondered carefully designed experiment will help to fully understand this problem.

This is a very old question I guess. See what your intention. If you do not plant to work on solve this , you can choose any avenues to force it close (e.g. one of widely cited papaer of Twine et al., 2000, AFM), then use the data to do other tasks (eg. upsacleing spatially or temporally). But if you want to slove this un-imbalance, you may need to do the experiment by yourself (e.g. comparing different soil heat flux estimation methods or vertical air heat storgae,etc). There are a few paper which are vert helpful, e.g. Foken et al., 2008, Ecological Applications,18: 1351-1367. Hope it is helpful.