Gust factor based on research aircraft measurements: A new methodology applied to the Arctic marine boundary layer

Gust Factors in the Marine Arctic

Irene Suomi, Christof Lüpkes, Jörg Hartmann, Timo Vihma, Sven-Erik Gryning, Carl Fortelius

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

There is as yet no standard methodology for measuring wind gusts from a moving platform. To address this, we have developed a method to derive gusts from research aircraft data. First we evaluated four different approaches, including Taylor's hypothesis of frozen turbulence, to derive the gust length-scales that correspond to the gust time-scales, namely the gust duration (s) and the sample period (typically 10 min). The novelty of our method lies in using peak factors (deviation of the gust from the mean wind speed normalized by the local turbulence) to convert between the scales. After devising a way to derive the gust length-scales, we calculated the gust factors from aircraft observations and tested them against those from four parametrizations originally developed for weather stations. Three of them performed well (R2=0.66 or higher), while the fourth overestimated the gust factors in unstable conditions (R2=0.52). The mean errors for all methods were low, from -0.02 to 0.05, indicating that wind gust factors can indeed be measured from research aircraft. Moreover, we showed that aircraft can provide gust measurements within the whole boundary layer, if horizontal legs are flown at multiple levels over the same track. This is a significant advance, as gust measurements are usually limited to heights reached by weather masts. In unstable conditions over the open ocean, the gust factor was nearly constant with height throughout the boundary layer, the near-surface values only slightly exceeding those at upper levels. Furthermore, we found gust factors to be strongly dependent on surface roughness conditions, which differed between the open ocean and sea ice in the Arctic marine environment. The roughness effect on the gust factor was stronger than the effect of boundary-layer stability.
Original languageEnglish
JournalRoyal Meteorological Society. Quarterly Journal
Volume142
Issue number701
Pages (from-to)2985–3000
Number of pages16
ISSN0035-9009
DOIs
Publication statusPublished - 2016

Keywords

  • Aircraft measurements
  • Arctic
  • Gust factor
  • Marine atmospheric boundary layer

Cite this

@article{5062dcb0c2cb45f99e4c9fa079bbee36,
title = "Gust factor based on research aircraft measurements: A new methodology applied to the Arctic marine boundary layer: Gust Factors in the Marine Arctic",
abstract = "There is as yet no standard methodology for measuring wind gusts from a moving platform. To address this, we have developed a method to derive gusts from research aircraft data. First we evaluated four different approaches, including Taylor's hypothesis of frozen turbulence, to derive the gust length-scales that correspond to the gust time-scales, namely the gust duration (s) and the sample period (typically 10 min). The novelty of our method lies in using peak factors (deviation of the gust from the mean wind speed normalized by the local turbulence) to convert between the scales. After devising a way to derive the gust length-scales, we calculated the gust factors from aircraft observations and tested them against those from four parametrizations originally developed for weather stations. Three of them performed well (R2=0.66 or higher), while the fourth overestimated the gust factors in unstable conditions (R2=0.52). The mean errors for all methods were low, from -0.02 to 0.05, indicating that wind gust factors can indeed be measured from research aircraft. Moreover, we showed that aircraft can provide gust measurements within the whole boundary layer, if horizontal legs are flown at multiple levels over the same track. This is a significant advance, as gust measurements are usually limited to heights reached by weather masts. In unstable conditions over the open ocean, the gust factor was nearly constant with height throughout the boundary layer, the near-surface values only slightly exceeding those at upper levels. Furthermore, we found gust factors to be strongly dependent on surface roughness conditions, which differed between the open ocean and sea ice in the Arctic marine environment. The roughness effect on the gust factor was stronger than the effect of boundary-layer stability.",
keywords = "Aircraft measurements, Arctic, Gust factor, Marine atmospheric boundary layer",
author = "Irene Suomi and Christof L{\"u}pkes and J{\"o}rg Hartmann and Timo Vihma and Sven-Erik Gryning and Carl Fortelius",
year = "2016",
doi = "10.1002/qj.2880",
language = "English",
volume = "142",
pages = "2985–3000",
journal = "Quarterly Journal of the Royal Meteorological Society",
issn = "0035-9009",
publisher = "RMetS, Royal Meteorological Society",
number = "701",

}

Gust factor based on research aircraft measurements: A new methodology applied to the Arctic marine boundary layer : Gust Factors in the Marine Arctic. / Suomi, Irene; Lüpkes, Christof; Hartmann, Jörg; Vihma, Timo; Gryning, Sven-Erik; Fortelius, Carl.

In: Royal Meteorological Society. Quarterly Journal, Vol. 142, No. 701, 2016, p. 2985–3000.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Gust factor based on research aircraft measurements: A new methodology applied to the Arctic marine boundary layer

T2 - Gust Factors in the Marine Arctic

AU - Suomi, Irene

AU - Lüpkes, Christof

AU - Hartmann, Jörg

AU - Vihma, Timo

AU - Gryning, Sven-Erik

AU - Fortelius, Carl

PY - 2016

Y1 - 2016

N2 - There is as yet no standard methodology for measuring wind gusts from a moving platform. To address this, we have developed a method to derive gusts from research aircraft data. First we evaluated four different approaches, including Taylor's hypothesis of frozen turbulence, to derive the gust length-scales that correspond to the gust time-scales, namely the gust duration (s) and the sample period (typically 10 min). The novelty of our method lies in using peak factors (deviation of the gust from the mean wind speed normalized by the local turbulence) to convert between the scales. After devising a way to derive the gust length-scales, we calculated the gust factors from aircraft observations and tested them against those from four parametrizations originally developed for weather stations. Three of them performed well (R2=0.66 or higher), while the fourth overestimated the gust factors in unstable conditions (R2=0.52). The mean errors for all methods were low, from -0.02 to 0.05, indicating that wind gust factors can indeed be measured from research aircraft. Moreover, we showed that aircraft can provide gust measurements within the whole boundary layer, if horizontal legs are flown at multiple levels over the same track. This is a significant advance, as gust measurements are usually limited to heights reached by weather masts. In unstable conditions over the open ocean, the gust factor was nearly constant with height throughout the boundary layer, the near-surface values only slightly exceeding those at upper levels. Furthermore, we found gust factors to be strongly dependent on surface roughness conditions, which differed between the open ocean and sea ice in the Arctic marine environment. The roughness effect on the gust factor was stronger than the effect of boundary-layer stability.

AB - There is as yet no standard methodology for measuring wind gusts from a moving platform. To address this, we have developed a method to derive gusts from research aircraft data. First we evaluated four different approaches, including Taylor's hypothesis of frozen turbulence, to derive the gust length-scales that correspond to the gust time-scales, namely the gust duration (s) and the sample period (typically 10 min). The novelty of our method lies in using peak factors (deviation of the gust from the mean wind speed normalized by the local turbulence) to convert between the scales. After devising a way to derive the gust length-scales, we calculated the gust factors from aircraft observations and tested them against those from four parametrizations originally developed for weather stations. Three of them performed well (R2=0.66 or higher), while the fourth overestimated the gust factors in unstable conditions (R2=0.52). The mean errors for all methods were low, from -0.02 to 0.05, indicating that wind gust factors can indeed be measured from research aircraft. Moreover, we showed that aircraft can provide gust measurements within the whole boundary layer, if horizontal legs are flown at multiple levels over the same track. This is a significant advance, as gust measurements are usually limited to heights reached by weather masts. In unstable conditions over the open ocean, the gust factor was nearly constant with height throughout the boundary layer, the near-surface values only slightly exceeding those at upper levels. Furthermore, we found gust factors to be strongly dependent on surface roughness conditions, which differed between the open ocean and sea ice in the Arctic marine environment. The roughness effect on the gust factor was stronger than the effect of boundary-layer stability.

KW - Aircraft measurements

KW - Arctic

KW - Gust factor

KW - Marine atmospheric boundary layer

U2 - 10.1002/qj.2880

DO - 10.1002/qj.2880

M3 - Journal article

VL - 142

SP - 2985

EP - 3000

JO - Quarterly Journal of the Royal Meteorological Society

JF - Quarterly Journal of the Royal Meteorological Society

SN - 0035-9009

IS - 701

ER -