The authors have adequately addressed referee comments, but I feel that the manuscript requires further improvement for publication in Biogeosciences. I hesitate to accept a paper that states 'The promise of seamless land-sea observations of surface heat fluxes offered by the approach appears to warrant investing the required effort.' as the last line of the Abstract, and 'preliminary development' at the end of the Introduction. A published manuscript should be complete. Much of the manuscript reads like an extensive justification of the simplifications used, with hypothetical explanations for why the approach often fails. One way of adjusting the manuscript emphasize the novelty of the approach is to place it in a framework where the flux estimates are shown to (approximately) agree regardless the (rather substantial) assumptions required by the approach, which simultaneously defends the assumptions while leading to future research in investigating why the approach works or fails. I also feel that some key references, listed below, have been missed and that the manuscript still needs improvements in specific areas.

On line 54, 'appear to fall' is not sufficiently specific. Evaporation routines can be classified with more rigor. I also note a critical new analysis by the Salvucci group (listed in References below) that does not rely on surface parameterization. A table of existing approaches would emphasize the novelty of the current approach.

Equation 5 requires further justification with respect to the dissimilarity between kH and kE. Note Katul et al. 1995 (below) and related references.

Define ‘radically different space’ on line 155.

On line 160, advective fluxes occur across a range of scales in space.

On line 168 ‘it is important to appreciate that the landscape heterogeneity is likely to increase with scale’: the relationship between landscape heterogeneity and scale can be quantified for the 30 study towers.

On line 240 and elsewhere, is there a relationship between spatial heterogeneity or representativeness and lack of fit?

On line 245, data rejection descriptions best belong in the Methods section.

I disagree with line 408, a relatively straightforward investigation of representativeness and/or spatial variability for thirty towers is likely to add insight into the findings. We performed such an analysis for 173 ecosystems in Stoy et al. (2013, AFM) and it wasn’t too onerous. Likewise, it is extremely straightforward to find if there is a relationship between tower height and goodness of fit on line 415.

On line 465 and elsewhere, maybe just remove the discussion of non-terrestrial fluxes if there is no basis for comparison.

In figure 4, I am assuming that the x axis is month.

References
Fisher, J.B., Tu, K. and Baldocchi, D.D., 2008a. Global estimates of the land-atmosphere water flux based on monthly AVHRR and ISLSCP-II data, validated at 16 FLUXNET sites. Remote Sensing of Environment, 112(3): 901-919.

Gao, H., Tang, Q., Ferguson, C.R., Wood, E.F. and Lettenmaier, D.P., 2010. Estimating the water budget of major US river basins via remote sensing. International Journal of Remote Sensing, 31(14): 3955-3978.

Katul, G., Goltz, S., Hsieh, C.-I., Cheng, Y., Mowry, F., & Sigmon, J. (1995). Estimation of surface heat and momentum fluxes using the flux-variance method above uniform and non-uniform terrain. Boundary-Layer Meteorology, 74(3), 237–260. doi:10.1007/BF00712120

Jang, K., Kang, S., Kim, J., Lee, C.B., Kim, T., Kim, J., Hirata, R. and Saigusa, N., 2010. Mapping evapotranspiration using MODIS and MM5 Four-Dimensional Data Assimilation. Remote Sensing of Environment, 114(3): 657-673.

Sahoo, A.K., Pan, M., Troy, T.J., Vinukollu, R.K., Sheffield, J. and Wood, E.F., 2011. Reconciling the global terrestrial water budget using satellite remote sensing. Remote Sensing of Environment, 115(8): 1850-1865.

Salvucci, G.,D., and P. Gentine, 2013. Emergent relation between surface vapor conductance and relative humidity profiles yields evaporation from weather data, Proceedings of the National Academy of Sciences, 110 (16), 6287-6291, DOI: 10.1073/pnas.1215844110

Su, Z., 2002. The Surface Energy Balance System (SEBS) for estimation of turbulent heat fluxes. Hydrology and Earth System Sciences, 6: 85-99.

Vinukollu, R.K., Wood, E.F., Ferguson, C.R. and Fisher, J.B., 2011. Global estimates of evapotranspiration for climate studies using multi-sensor remote sensing data: Evaluation of three process-based approaches. Remote Sensing of Environment, 115: 801-823.

The authors have made a number of improvements to the manuscript over multiple iterations of review. Whereas I feel that there is still work to do on this particular analysis, the same could be said for any field of science. This manuscript improves our understanding of latent heat modeling by approaching the challenge from a viewpoint that differs somewhat from the standard approach, and in this way is a valuable contribution to research.

Sincerely,
Paul C. Stoy