BOUNDARY-LAYER ENTRAINMENT ESTIMATION THROUGH ASSIMILATION OF RADIOSONDE AND MICROMETEOROLOGICAL DATA INTO A MIXED-LAYER MODEL

摘要

In this study we estimate boundary-layer growth and entrainmenl by combining radiosonde and micrometeorological observations with a simple coupled boundary-layer and land surface model. A variational (smoothing) approach is used to find the optimal estimate of entrainment over the daytime window. This method is appealing because it accounts for the uncertainty in the various data streams, while enforcing the dynamics of the model (i.e., water and energy budgets in the boundary layer, mixed-layer growth, etc.). The traditional variational framework was modified in this study to include an ensemble approach, which not only yields a (mean) estimate of entrainment, but a measure of its uncertainty as well. The methodology is applied to a field experiment site in Kansas. Results from this study indicate a much larger ratio of entrainment to surface fluxes compared to early literature values from other sites. However, our results are consistent with recent estimates at the site using independent estimation methods. In tests where radiosonde data were withheld, reasonable skill in entrainment estimation was still shown, suggesting the potential for more widespread applications where only micrometeorological data are available. Finally, the data assimilation framework presented here has not traditionally been used in atmospheric boundary-layer studies, and may provide a useful approach for studying other aspects of the boundary layer in the future.