### Abstract

This note evaluates the numerical schemes used for computing the axial component of the mountain torque from gridded global surface pressure and topography datasets. It is shown that the two formulas of the mountain torque based on (i) an integral of the product of the surface pressure and the gradient of topography, and (ii) an integral of the product of the topography and the surface pressure gradient, should produce identical results if a centered even-ordered finite-difference scheme or the spectral method is used to evaluate the integrand. Noncentered finite-difference schemes are not recommended not only because they produce extremely large errors but also because they produce different results for the two formulas. When compared with the benchmark calculation using the spectral method, it is found that the centered fourth-order finite-difference scheme is an efficient and generally accurate approximation for practical applications. Using the data from NCEP-NCAR reanalysis, the finite-difference schemes generally underestimate the global mountain torque compared to the benchmark. This negative error is interpreted as due to the asymmetry in the distribution of surface pressure and in the steepness of the topography between the western and eastern slopes of the mountains.

Original language | English (US) |
---|---|

Pages (from-to) | 4005-4009 |

Number of pages | 5 |

Journal | Monthly Weather Review |

Volume | 136 |

Issue number | 10 |

DOIs | |

State | Published - 2008 |

Externally published | Yes |

### Fingerprint

### ASJC Scopus subject areas

- Atmospheric Science

### Cite this

*Monthly Weather Review*,

*136*(10), 4005-4009. https://doi.org/10.1175/2008MWR2359.1

**On the computation of the mountain torque from gridded global datasets.** / Huang, Huei-Ping; Weickmann, Klaus M.

Research output: Contribution to journal › Article

*Monthly Weather Review*, vol. 136, no. 10, pp. 4005-4009. https://doi.org/10.1175/2008MWR2359.1

}

TY - JOUR

T1 - On the computation of the mountain torque from gridded global datasets

AU - Huang, Huei-Ping

AU - Weickmann, Klaus M.

PY - 2008

Y1 - 2008

N2 - This note evaluates the numerical schemes used for computing the axial component of the mountain torque from gridded global surface pressure and topography datasets. It is shown that the two formulas of the mountain torque based on (i) an integral of the product of the surface pressure and the gradient of topography, and (ii) an integral of the product of the topography and the surface pressure gradient, should produce identical results if a centered even-ordered finite-difference scheme or the spectral method is used to evaluate the integrand. Noncentered finite-difference schemes are not recommended not only because they produce extremely large errors but also because they produce different results for the two formulas. When compared with the benchmark calculation using the spectral method, it is found that the centered fourth-order finite-difference scheme is an efficient and generally accurate approximation for practical applications. Using the data from NCEP-NCAR reanalysis, the finite-difference schemes generally underestimate the global mountain torque compared to the benchmark. This negative error is interpreted as due to the asymmetry in the distribution of surface pressure and in the steepness of the topography between the western and eastern slopes of the mountains.

AB - This note evaluates the numerical schemes used for computing the axial component of the mountain torque from gridded global surface pressure and topography datasets. It is shown that the two formulas of the mountain torque based on (i) an integral of the product of the surface pressure and the gradient of topography, and (ii) an integral of the product of the topography and the surface pressure gradient, should produce identical results if a centered even-ordered finite-difference scheme or the spectral method is used to evaluate the integrand. Noncentered finite-difference schemes are not recommended not only because they produce extremely large errors but also because they produce different results for the two formulas. When compared with the benchmark calculation using the spectral method, it is found that the centered fourth-order finite-difference scheme is an efficient and generally accurate approximation for practical applications. Using the data from NCEP-NCAR reanalysis, the finite-difference schemes generally underestimate the global mountain torque compared to the benchmark. This negative error is interpreted as due to the asymmetry in the distribution of surface pressure and in the steepness of the topography between the western and eastern slopes of the mountains.

UR - http://www.scopus.com/inward/record.url?scp=57149139440&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=57149139440&partnerID=8YFLogxK

U2 - 10.1175/2008MWR2359.1

DO - 10.1175/2008MWR2359.1

M3 - Article

AN - SCOPUS:57149139440

VL - 136

SP - 4005

EP - 4009

JO - Monthly Weather Review

JF - Monthly Weather Review

SN - 0027-0644

IS - 10

ER -