scholarly journals A probabilistic model for estimating ocean-spray distribution in extreme tropical cyclone winds

MAUSAM ◽  
2021 ◽  
Vol 48 (4) ◽  
pp. 489-498
Author(s):  
JAMES LIGHT HILL
Keyword(s):  
Tropical Cyclone ◽  
Initial Temperature ◽  
Mechanical Energy ◽  
Spray Cooling ◽  
Wind Speeds ◽  
Extreme Wind ◽  
Future Global Warming ◽  
Ocean Spray ◽  
Spray Distribution ◽  
Extreme Wind Speeds

ABSTRACT. Serious gaps in knowledge about ocean spray at wind speeds over 28 m/s remain difficult to fill by observation or experiment; yet refined study of the thermodynamics of Tropical Cyclones (including typhoons and hurricanes) requires assessment of the hypothesis that ‘spray cooling’ at extreme wind speeds may act to reduce (i) the initial temperature of saturated air rising in the eyewall and so also (ii) the input of mechanical energy into the airflow as a whole. Such progressive reductions at higher speeds could, for example, make any possible influence, of future global warming on Tropical Cyclone intensification largely se1f-limiting. In order to help in extrapolation of knowledge on ocean spray to extreme wind speeds, a probabilistic analysis is introduced which allows for the effects of gusts, gravity and evaporation on droplet distributions yet all other respect is as simple as possible. Preliminary indications from this simplified analysis appear to confirm the potential importance of spray cooling.    

Microphysics-Based Bulk Parameterizations of Enthalpy and Momentum Fluxes for Tropical Cyclones

2020 ◽  
Author(s):  
Sydney Sroka ◽  
Kerry Emanuel
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
State Of The Art ◽  
Sea Spray ◽  
Wind Speeds ◽  
Extreme Wind ◽  
Momentum Fluxes ◽  
Forecast Models ◽  
Extreme Wind Speeds ◽  
Tropical Cyclone Boundary Layer

<p>Despite the powerful influence that sea spray has on air-sea enthalpy and momentum fluxes, most state-of-the-art tropical cyclone forecast models do not incorporate the microphysics of sea spray evaporation into their boundary layer flux schemes. Since the air-sea enthalpy and momentum fluxes control a tropical cyclone’s intensification rate, increasing the accuracy of the associated bulk parameterizations is crucially important for improving forecast skill. New microphysics-based bulk parameterizations for enthalpy and momentum flux through the tropical cyclone boundary layer are developed from a set of prognostic evaporation equations and numerical simulations of evaporating, multiphase flow subject to extreme wind speeds. The microphysics-based parameterizations are computationally inexpensive and are functions of the local environmental conditions; these features allow forecast models to efficiently vary the air-sea enthalpy and momentum fluxes in space and time. By developing microphysics-based bulk parameterizations, the influence that sea spray exerts on tropical cyclone intensification can be more accurately simulated and intensity forecasts could be improved.</p>

Forecasting of Tornadoes and Downbursts

2020 ◽  
Author(s):  
Djordje Romanic
Keyword(s):  
Chaos Theory ◽  
Prediction Models ◽  
Weather Prediction ◽  
Small Scale ◽  
Weather Forecasts ◽  
Wind Speeds ◽  
The Past ◽  
Extreme Wind ◽  
Extreme Wind Speeds ◽  
Numerical Weather Prediction Models

Tornadoes and downbursts cause extreme wind speeds that often present a threat to human safety, structures, and the environment. While the accuracy of weather forecasts has increased manifold over the past several decades, the current numerical weather prediction models are still not capable of explicitly resolving tornadoes and small-scale downbursts in their operational applications. This chapter describes some of the physical (e.g., tornadogenesis and downburst formation), mathematical (e.g., chaos theory), and computational (e.g., grid resolution) challenges that meteorologists currently face in tornado and downburst forecasting.

Midlatitude cyclones in convection permitting climate simulations: the added value offered for extreme wind speeds and sting-jets

2021 ◽  
Author(s):  
Colin Manning ◽  
Elizabeth Kendon ◽  
Hayley Fowler ◽  
Nigel Roberts ◽  
Segolene Berthou ◽  
...  
Keyword(s):  
Climate Model ◽  
Surface Wind ◽  
Added Value ◽  
Large Contribution ◽  
High Wind ◽  
Wind Speeds ◽  
Wind Gusts ◽  
Climate Simulations ◽  
Extreme Wind ◽  
Extreme Wind Speeds

<p>Extra-tropical windstorms are one of the costliest natural hazards affecting Europe, and windstorms that develop a phenomenon known as a sting-jet account for some of the most damaging storms. A sting-jet (SJ) is a mesoscale core of high wind speeds that occurs in particular types of cyclones, specifically Shapiro-Keyser (SK) cyclones, and can produce extremely damaging surface wind gusts. High-resolution climate models are required to adequately model SJs and so it is difficult to gauge their contribution to current and future wind risk. In this study, we develop a low-cost methodology to automate the detection of sting jets, using the characteristic warm seclusion of SK cyclones and the slantwise descent of high wind speeds, within pan-European 2.2km convection-permitting climate model (CPM) simulations. Following this, we quantify the contribution of such storms to wind risk in Northern Europe in current and future climate simulations, and secondly assess the added value offered by the CPM compared to a traditional coarse-resolution climate model. This presentation will give an overview of the developed methods and the results of our analysis.</p><p>Comparing with observations, we find that the representation of wind gusts is improved in the CPM compared to ERA-Interim reanalysis data. Storm severity metrics indicate that SK cyclones account for the majority of the most damaging windstorms. The future simulation produces a large increase (>100%) in the number of storms exceeding high thresholds of the storm metric, with a large contribution to this change (40%) coming from windstorms in which a sting-jet is detected. Finally, we see a systematic underestimation in the GCM compared to the CPM in the frequency of extreme wind speeds at 850hPa in the cold sector of cyclones, likely related to better representation of sting-jets and the cold conveyor belt in the CPM. This underestimation is between 20-40% and increases with increasing wind speed above 35m/s. We conclude that the CPM adds value in the representation of severe surface wind gusts, providing more reliable future projections and improved input for impact models.</p>

Changes in extreme wind speeds in NW Europe simulated by generalized linear models

2005 ◽  
Vol 83 (1-4) ◽  
pp. 121-137 ◽  
Author(s):  
Z. Yan ◽  
S. Bate ◽  
R. E. Chandler ◽  
V. Isham ◽  
H. Wheater
Keyword(s):  
Generalized Linear Models ◽  
Linear Models ◽  
Wind Speeds ◽  
Extreme Wind ◽  
Extreme Wind Speeds ◽  
Nw Europe

scholarly journals At What Time of Day Do Daily Extreme Near-Surface Wind Speeds Occur?

2014 ◽  
Vol 27 (11) ◽  
pp. 4226-4244 ◽  
Author(s):  
Robert Fajber ◽  
Adam H. Monahan ◽  
William J. Merryfield
Keyword(s):  
Extreme Values ◽  
Mechanistic Model ◽  
Surface Wind ◽  
Time Of Day ◽  
Near Surface ◽  
Wind Speeds ◽  
Boundary Layer Processes ◽  
Early Afternoon ◽  
Extreme Wind ◽  
Extreme Wind Speeds

Abstract The timing of daily extreme wind speeds from 10 to 200 m is considered using 11 yr of 10-min averaged data from the 213-m tower at Cabauw, the Netherlands. This analysis is complicated by the tendency of autocorrelated time series to take their extreme values near the beginning or end of a fixed window in time, even when the series is stationary. It is demonstrated that a simple averaging procedure using different base times to define the day effectively suppresses this “edge effect” and enhances the intrinsic nonstationarity associated with diurnal variations in boundary layer processes. It is found that daily extreme wind speeds at 10 m are most likely in the early afternoon, whereas those at 200 m are most likely in between midnight and sunrise. An analysis of the joint distribution of the timing of extremes at these two altitudes indicates the presence of two regimes: one in which the timing is synchronized between these two layers, and the other in which the occurrence of extremes is asynchronous. These results are interpreted physically using an idealized mechanistic model of the surface layer momentum budget.

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