ASRAdvances in Science and ResearchASRAdv. Sci. Res.1992-0636Copernicus PublicationsGöttingen, Germany10.5194/asr-15-251-2018Comparison of seven wind gust parameterizations over the European part of RussiaComparison of seven wind gust parameterizations over the European part of RussiaKurbatovaMariamarja1702@gmail.comRubinsteinKonstantinGubenkoInnahttps://orcid.org/0000-0003-3173-6013KurbatovGrigoryHydrometeorological Center of Russia, Moscow, Russian FederationNuclear safety institute of the Russian Academy of Sciences, Moscow, Russian FederationFaculty of Physics M. V. Lomonosov Moscow State University, Moscow, Russian FederationMaria Kurbatova (marja1702@gmail.com)19November20181525125514February20186August20184November2018This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/This article is available from https://asr.copernicus.org/articles/15/251/2018/asr-15-251-2018.htmlThe full text article is available as a PDF file from https://asr.copernicus.org/articles/15/251/2018/asr-15-251-2018.pdf
Wind gusts are extreme events which can cause severe damage. Gusts can reach
significant values even during medium winds. However, numerical atmospheric
models are designed to reproduce average wind speed, not gusts. There are
several approaches to estimating wind gusts. Seven different methods are
applied to WRF-ARW model output. Results are compared to high-frequency wind
speed measurements using ultrasonic anemometers and temperature profiler
measurement at the same point in Moscow. Data gathered from synoptic station
network over the European part of Russia were also included in the analysis
to increase the statistics. None of the wind gust estimation methods shows
best results at every skill score. The proposed hybrid method shows good
balance between the probability of detection and the false alarm ratio estimates.
Introduction
Even when average wind speed is low gusts can reach significant values. Gusts
carry a high amount of wind energy and can cause severe damage and affect transport
functioning. The greatest damage from storms is usually caused
by strong wind gusts leading to constructions collapse and falling trees. For
example, due to the storm over Moscow in May 2017, 16 people died, and according to
insurance companies, the economic loss exceeded 25 million roubles
(≈350000 EUR). Major damage appeared because of torn-off roofs,
weak constructions, breakage of power lines, trees falling on cars – the
reason for all of this was the strong wind. Early forecast of strong wind gusts can
help to organize preventive actions (strengthening structures, warning
people, etc.) to reduce damage, so realistically forecasting wind gusts is a very
important task of numerical meteorology. However, there is a variety of
methods for wind gust estimation. There is a need to know the applicability
of the method used in a particular case. In this study we analyse different
aspects of wind gust forecast approaches.
There are two ways to use numerical model output: to perform statistical
postprocessing or to create a physical model of wind gust formation. The
undoubted advantage of the second approach is that these methods help to better
understand the nature and mechanisms of the formation of this natural
phenomenon. Let us analyse this group of methods in more detail.
Wind gust parameterizations
Dynamical wind gust estimation methods can be divided into two groups.
Methods in the first group are based on the fact that wind gusts are related
to atmospheric turbulence and therefore can be estimated on the basis of
turbulent characteristics determined within the parameterization of the
atmospheric boundary layer. Turbulent kinetic energy (TKE) represents a
deviation of the instantaneous wind from the mean, so we can consider TKE as
wind speed dispersion. From the assumption that the wind speed distribution
is normal, the following formula can be proposed (this method is further
referred to as TKE):
wge=U+3σ=U+3q,
where “wge” is the wind gust estimate, U is average wind speed, σ is
the standard deviation of wind speed, and q is TKE. If there is no TKE in the model
output, we can use the relation between TKE and friction velocity to estimate
the variance . If we assume that the TKE in the model
represents the maximum deviation of instant wind from the mean, we can get
the following estimate (this method is further referred to
as TKE-2):
wge=U+2q.
Another TKE-based parameterization was developed by (this
method is further referred to as Schreur):
wge=U1+grσ2qU.
Based on the observation data fit:
g=1.42+0.3013ln990Ut-4rσ=1-0.069exp-2.3Utzexp-2.3Utz0.555,
where t=3 s is gust duration and z=10 m is height above ground.
Methods in the second group are based on an assumption that gusts are the
result of air particles deflection from higher levels and carry speed from
those levels. proposed to use the wind speed from the
atmospheric boundary layer height (this method is further referred to as PBLH).
In the case of deep convection, vertical motion as well as precipitation should
be taken into account (this method is further referred
to as Nakamura):
wge=α∫0H2gΔθθ+qrdz+βU(H),
where H is boundary layer height, and qris rain mixing ratio,
suggests α=0.25 and β=0.85.
suggests taking into account the energy of particles
that can reach the surface (this method is further referred to as Brasseur):
wge=maxUzp,
for the levels zp satisfying Eq. ():
1zp∫0zpq(z)dz≥∫0zpgΔθv(z)Θv(z)dz,
where θv is the virtual potential temperature.
The methods using TKE are not applicable to the prediction of gusts
associated with strong convection. However, they work well in cases with the
turbulence of mechanical origin. Our preliminary study showed the first TKE
method to give good results. Otherwise, particle deflection methods are
usually considered in cases of convection. The Brasseur method looks to be the
most physically developed. To combine advantages of both groups of methods we
propose a hybrid method:
wge=U+3q,Ri>0maxUzp,Ri≤0,
where zp satisfies Eq. (). We use the Richardson number Ri to
separate the types of the instability of the atmospheric boundary layer.
Data and methodsMeasurement data and numerical model
Unfortunately, the measurements that allow the dynamics of wind
gust formation to be studied are rather sparse. In this paper, we use data from
high-frequency wind speed measurements conducted at the Physics Department of
Moscow State University in Moscow. The measurements are carried out at a
frequency of 50 Hz with ultrasonic anemometers USA-1 (Metek). At the same
point, the temperature profiles up to 600 m height are measured using a
microwave temperature profiler MTP-5.
Wind gusts are observed by synoptic stations network but data contain many
omissions (only 25 % reports contain gust information) and have 3 h time
resolution. In addition, gusts associated with the squall lines may have a
small spatial extent, so they are not captured by data. However, the network
provides the biggest data set over the European part of Russia: 2189 stations
were used in this work (see Fig. ).
Wind gust estimation methods are realized using WRF-ARW version 3.7.1
model output. It has good estimations of the forecast
of meteorological values in the atmospheric boundary layer
. The model domain (Fig. ) covers the
European part of Russia with a spatial resolution of 18 km. The initial and
boundary conditions are the NCEP analysis with a
spatial resolution of 0.5∘. The model configuration was chosen on the
basis of studies in which an accurate description of the wind speed is important
. The model parameterizations include
microphysics , radiation – RRTMG ,
soil – NOAH , Bates–Miller convection ,
and boundary layer – MYNN .
Model domain topographic height. Points are synoptic stations. Red
square shows the area used for analyses.
Method of evaluation
Seven methods described in Sect. 2 were applied to WRF model output (3 h
time step) at each grid point. To obtain mean wind speed values from
the four nearest model grid points are bilinearly interpolated to the
measurement point. To obtain the wind gust estimation, the maximum value from the four
nearest grid points is taken. Gust observation is at a maximum over at 10 min period from a 3 s average at the point with high-frequency measurements. Temperature
profile measurements are averaged for the same 10 min intervals.
For comparison with the data from the synoptic network, the area shown on
Fig. was divided into 1∘× 1∘ cells in
latitude and longitude. The value in the cell is maximum gust from all
stations and from all computational model points in this cell. If there were no observations in the cell, it is not taken into
account. This sort of averaging was done to reduce phase errors. It can lead
to overestimating gusts, especially in highly variable terrain. However, the
analysed area is mostly relatively flat. The wind gust exceeding of the
preset threshold 15 m s-1 is taken as an actual event. The probability of
detection, false alarm ratio, Pierce's skill score (PSS), and equitable threat
score (ETS) were calculated based on the contingency table compilation.
Time series for 4–6 June 2016 of measured wind speed with 3 s
averaging and one forecast starting at 03:00 LT on 4 June of wind
speed and gusts by seven methods described in Sect. 2.
Measured wind gust factor and potential temperature gradient in
the lowest 100 m in Moscow during July 2016.
Comparison with high-frequency observations
Figure shows the example of high-frequency wind speed
measurements and the forecast of wind speed and gusts calculated by seven
parameterizations. Mean wind speed is quite well reproduced by the model.
Figure shows an interval U±3q too; thus in the TKE
method q is taken as the standard deviation of wind speed. Analysis
of 1-year data (0–48 h lead-time forecasts starting every 24 h) showed that
74 % of all measurements fit this interval. Most deviations from
observations are due to time-phase errors of mean wind speed. Though most
methods capture the strongest gust in the shown period, they overestimate
them most of the time.
Figure presents the measured gust factor and the potential
temperature gradients in the lower 100 m layer. It does not show a direct
connection between them. However gust factor spreading increases if the potential
temperature gradient decreases.
Estimations of wind gust over 15 m s-1 using seven
different methods for three winter and three summer months over the European part
of Russia.
Comparison with synoptic stations data
Figure shows skill scores of 24 h forecasts of wind gusts
exceeding 15 m s-1 for the three winter and three summer months in 2016.
Methods using the principle of deviation from higher levels show a higher
probability of detection of wind gusts but also a greater number of false
alarms. ETS and PSS are low for all methods, especially for summer. Lower
performance in summer can be due to the difficulty of describing convective winds.
Convective events might not be captured by the model due to its
resolution. ETS is slightly better for TKE using methods since they have a
lower false alarm ratio. PSS is slightly greater for particle deflection
methods since they have higher probability of detection. Despite the fact
that the hybrid method does not show the best estimate, it has a greater
probability of detection than TKE methods and a lower false alarm ratio then
particle deflection methods. It can be seen that none of the existing methods
provide high performance in every skill score, so there is a need for
further investigation of gusts.
Conclusions
Seven wind gust estimation methods are applied to the WRF-ARW model output. A new
hybrid method was proposed. It shows a good balance between the probability
of detection and the false alarm ratio estimates. The conducted research
shows the necessity of further studying the mechanisms of formation and
methods for forecasting of wind gusts.
Data used in this study are not publicly available. Please
contact authors for further information.
MK performed numerical experiments, statistical estimations,
analysis of the results, and wrote the paper. IG carried out numerical experiments
and analysis of the results. KR helped in the formulation of the task, analysis
of the results, and writing of the paper. GK performed and analysed high-frequency observations.
The authors declare that they have no conflict of interest.
This article is part of the special issue “17th EMS Annual Meeting:
European Conference for Applied Meteorology and Climatology 2017”. It is a
result of the EMS Annual Meeting: European Conference for Applied Meteorology
and Climatology 2017, Dublin, Ireland, 4–8 September 2017.
Acknowledgements
This work is partly supported by RFBR according to the research projects 16-05-00822,
16-05-00704, 18-05-00044. It was also supported by EMS through YSTA. Edited by: Sabrina Wahl
Reviewed by: Ken Mylne and one anonymous referee
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