The Probability Distribution of Land Surface Wind Speeds

Monahan, Adam H.; He, Yanping; McFarlane, N. A.; Dai, Aiguo

doi:10.1175/2011jcli4106.1

Cited by 49 publications

(53 citation statements)

References 35 publications

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“…We did, however, choose airflow speeds that the rat might encounter in the natural environment. Meteorological studies find typical land-surface wind speeds between 0 and 5 m s −1 (Monahan et al, 2011). We confirmed this range using a hot wire anemometer (Omega, model HHF42, resolution ±0.1 m s −1 ) to measure airflow speeds in locations where rats are expected (bushes, dumpsters, fields, etc.).…”

Section: Methodssupporting

confidence: 73%

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Mechanical responses of rat vibrissae to airflow

Graff

Hartmann

2016

Journal of Experimental Biology

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The survival of many animals depends in part on their ability to sense the flow of the surrounding fluid medium. To date, however, little is known about how terrestrial mammals sense airflow direction or speed. The present work analyzes the mechanical response of isolated rat macrovibrissae (whiskers) to airflow to assess their viability as flow sensors. Results show that the whisker bends primarily in the direction of airflow and vibrates around a new average position at frequencies related to its resonant modes. The bending direction is not affected by airflow speed or by geometric properties of the whisker. In contrast, the bending magnitude increases strongly with airflow speed and with the ratio of the whisker's arc length to base diameter. To a much smaller degree, the bending magnitude also varies with the orientation of the whisker's intrinsic curvature relative to the direction of airflow. These results are used to predict the mechanical responses of vibrissae to airflow across the entire array, and to show that the rat could actively adjust the airflow data that the vibrissae acquire by changing the orientation of its whiskers. We suggest that, like the whiskers of pinnipeds, the macrovibrissae of terrestrial mammals are multimodal sensors -able to sense both airflow and touch -and that they may play a particularly important role in anemotaxis.

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Section: Methodssupporting

confidence: 73%

“…5), certainly sensitive enough to respond to typical air currents on land (Monahan et al, 2011). Furthermore, because most whiskers are oriented concave forward or concave down, the mechanical response to airflow will be amplified compared with a concave backwards orientation.…”

Section: Discussionmentioning

confidence: 99%

Mechanical responses of rat vibrissae to airflow

Graff

Hartmann

2016

Journal of Experimental Biology

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“…Mahrt 1998;Fernando and Weil 2010;Monahan et al 2011;Sun et al 2012;Mahrt 2014;Bonin et al 2015;Acevedo et al 2015;Hooijdonk et al 2015). The weakly stable boundary layer (WSBL) generally occurs when winds are strong or when clouds are present.…”

Section: Introductionmentioning

confidence: 99%

Early Warning Signals for Regime Transition in the Stable Boundary Layer: A Model Study

Hooijdonk

Moene

Scheffer

et al. 2016

Boundary-Layer Meteorol

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The evening transition is investigated in an idealized model for the nocturnal boundary layer. From earlier studies it is known that the nocturnal boundary layer may manifest itself in two distinct regimes, depending on the ambient synoptic conditions: strongwind or overcast conditions typically lead to weakly stable, turbulent nights; clear-sky and weak-wind conditions, on the other hand, lead to very stable, weakly turbulent conditions. Previously, the dynamical behaviour near the transition between these regimes was investigated in an idealized setting, relying on Monin-Obukhov (MO) similarity to describe turbulent transport. Here, we investigate a similar set-up, using direct numerical simulation; in contrast to MO-based models, this type of simulation does not need to rely on turbulence closure assumptions. We show that previous predictions are verified, but now independent of turbulence parametrizations. Also, it appears that a regime shift to the very stable state is signaled in advance by specific changes in the dynamics of the turbulent boundary layer. Here, we show how these changes may be used to infer a quantitative estimate of the transition point from the weakly stable boundary layer to the very stable boundary layer. In addition, it is shown that the idealized, nocturnal boundary-layer system shares important similarities with generic non-linear dynamical systems that exhibit critical transitions. Therefore, the presence of other, generic early warning signals is tested as well. Indeed, indications are found that such signals are present in stably stratified turbulent flows.

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“…This decoupling also allows the residual layer to undergo inertial oscillations caused by the release from surface drag (e.g., Baas et al 2009Baas et al , 2010van de Wiel et al 2010); the resulting low-level jets (LLJs) are responsible for the large average wind speeds aloft. In fact, not only the mean, but the entire probability distribution of nearsurface wind speeds displays a marked diurnal cycle (Monahan et al 2011;He et al 2010He et al , 2012He et al , 2013. In addition to these diurnal variations associated with local dynamical processes, variability in the pressure gradient force associated with mesoscale and synoptic-scale systems can also produce wind speed extremes.…”

Section: Introductionmentioning

confidence: 99%

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

2014

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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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The Probability Distribution of Land Surface Wind Speeds

Cited by 49 publications

References 35 publications

Mechanical responses of rat vibrissae to airflow

Mechanical responses of rat vibrissae to airflow

Early Warning Signals for Regime Transition in the Stable Boundary Layer: A Model Study

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

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