New Approaches to the Parameterization of Gravity-Wave and Flow-Blocking Drag due to Unresolved Mesoscale Orography Guided by Mesoscale Model Predictability Research

Abstract

When surface flow impinges on orography with horizontal scales of ~1-500 km, a variety of mesoscale dynamical responses can result, including gravity waves, upstream blocking, flow splitting and lee vortices. These dynamics produce important drag forces on the larger scale atmosphere. Because global numerical weather and climate prediction (NWCP) models under-resolve orography at these scales, all credible NWCP systems must include parameterizations of these missing orographic mesoscale drag (OMD) forces. Recent evidence from mesoscale model simulations clearly indicates that OMD forces cannot be described as a purely deterministic response to upstream forcing, but instead can exhibit a range of values, time histories and states. Our long-term goals are (a) to build these new OMD dynamics delineated from mesoscale models into a new class of OMD parameterizations, (b) to embed those new parameterizations within Navy NWCP systems, and (c) to investigate whether improved time-mean OMD and new explicit OMD variability can improve NCWP skill in Navy global NWCP systems across a range of scales. The objective of this project is to develop a new class of subgrid-scale parameterizations of gravity-wave and flow-blocking drag due to flow incident upon unresolved mesoscale orography that (a) builds upon the existing OMD parameterization currently implemented in Navy NWCP models (Webster et al. 2003), but (b) modifies it s behavior in ways that both recognize and explicitly incorporate realistic distributions of possible OMD values that can arise for a given upstream flow environment, as deduced from fully nonlinear mesoscale model ensemble simulations.

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Document Details

Document Type
Technical Report
Publication Date
Sep 30, 2011
Accession Number
ADA557125

Entities

People

  • Stephen D. Eckermann

Organizations

  • United States Naval Research Laboratory

Tags

DTIC Thesaurus Topics

  • Altitude
  • Amplitude
  • Aspect Ratio
  • Climate Change
  • Dynamics
  • Flow
  • Froude Number
  • Gravity
  • Gravity Waves
  • Military Research
  • Orography
  • Physics
  • Pressure Distribution
  • Simulations
  • Space Sciences
  • Three Dimensional
  • Waves

Fields of Study

  • Environmental science

Readers

  • Ocean-Atmosphere Mesoscale Modeling, Data Assimilation, and Flux Boundary Layers