Data Assimilation Strategies in the Planetary Boundary Layer |
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| Authors: | Brian P Reen David R Stauffer |
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| Institution: | (1) NOAA/Earth Systems Research Laboratory, Boulder, CO, USA;(2) NOAA/CIRES, Boulder, CO, USA;(3) Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USA;(4) NOAA/Earth System Research Laboratory (ESRL)/Physical Sciences Division (PSD), Boulder, CO, USA |
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| Abstract: | We investigate the effect of the assimilation of surface and boundary-layer mass-field observations on the planetary boundary
layer (PBL) within a one-dimensional (1D) version of the non-hydrostatic Fifth-Generation Pennsylvania State University/National
Center for Atmospheric Research Mesoscale Model (MM5). We focus on the vertical extent and effects of mass-field nudging within
the PBL based on surface observations, and the added value of assimilating column mass observations within the PBL. Model
experiments for dynamic initialization and dynamic analysis are conducted and composited for 29 May, 6 June, and 7 June 2002
during the International H2O Project (IHOP) over the Southern Great Plains, U.S.A. Advantages are found when the data assimilation uses the innovation
(the difference between the modelled value and the observed value) calculated by comparing the surface mass-field observation
to the model value at the 2-m observation height rather than at the lowest model level. It is shown that this innovation can
be applied throughout the model-diagnosed PBL via nudging during free-convective conditions because of the well-mixed nature
of the PBL. However, in stable conditions, due to decreased vertical mixing the surface innovation may be best applied only
in a shallow layer adjacent to the surface. Surface air-temperature innovations were also applied to the top soil-layer temperature
to minimize disruption to the surface energy balance. In combination with the surface observations, the use of within-PBL
mass-field data assimilation improves the simulated PBL structure. |
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