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Maximum Wind Speed (maximum + wind_speed)
Selected AbstractsWind speed measurements and forest damage in Canton Zurich (Central Europe) from 1891 to winter 2007INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2010Tilo Usbeck Abstract The most severe damage to forests in central Europe occurs during winter storms that are caused by Northern Hemispheric mid-latitude cyclones. These winter storms have caused several catastrophic windthrows during the past four decades. Amounts of forest storm damage are believed to be a function of both the size of the forest and the storm intensity. To test this hypothesis, the Zurich region (city and canton) was chosen because long-term climate observation data is available for the region. The relationships between forest attributes, wind speed and forest damage were explored by comparing data on forests and wind speed from 107 winters with forest damage. Storm damage was defined as the proportion of damaged forests with respect to the growing stock. The variables: daily wind run (91 years), daily maximum hourly average wind speed (107 years) and peak gust wind speed (74 years) were homogenized with respect to high wind speed and related to levels of forest damage. High maximum wind speed at the end of the 19th century and at the beginning of the 20th century was followed by low maximum wind speed in the 1940s, 1960s and 1970s. Since then, maximum values have increased. Gusts (extremes of the maximum wind speed) increased from the beginning of the recordings in 1933 and peaked in the early 1990s. Forest damage due to winter storms is best correlated with peak wind speed. Gusts exceeding 40 m/s and resulting in catastrophic windthrow have increased in recent winters. Copyright © 2009 Royal Meteorological Society [source] Effects of a tropical cyclone on the distribution of hatchery-reared black-spot tuskfish Choerodon schoenleinii determined by acoustic telemetryJOURNAL OF FISH BIOLOGY, Issue 3 2010Y. Kawabata The effects of a tropical cyclone on the distribution of hatchery-reared black-spot tuskfish Choerodon schoenleinii were examined using acoustic telemetry. Nine fish were released in Urasoko Bay, Ishigaki Island, Japan, in September 2006, and another nine were released in June to July 2007, before a cyclone's passing through the area in September 2007. Data for the fish released in 2006 were used as the cyclone-inexperienced group to compare their distribution pattern to that of the 2007 cyclone-experienced group. Both groups of fish were monitored for up to 150 days. Of the nine fish in each group, four (44%) and two (22%) were monitored for over 150 days in the cyclone-inexperienced and the cyclone-experienced groups, respectively. Three of the five fish that had settled in the monitoring area left the area within a few days of the cyclone event. To estimate the time of disappearance of the fish, maximum wind speed during a period of 7 days (indicating the occurrence and intensity of the tropical cyclone), fish size and release year were evaluated as explanatory variables using a Cox proportional hazards model with Akaike's information criterion. The best predictive model included the effect of maximum wind speed. One fish that left the monitoring area displayed movement patterns related to strong winds, suggesting that wind-associated strong currents swept the fish away. No relationships were found between the movement patterns of the other two fish and any physical environmental data. The daily detection periods of one of the two fish gradually decreased after the cyclone hit, and this fish eventually left the monitoring area within 3 days, suggesting that it shifted to a habitat outside the monitoring area. These results indicate that tropical cyclones have both direct and indirect effects on the distribution of hatchery-reared C. schoenleinii. [source] Sea-land breeze development during a summer bora event along the north-eastern Adriatic coastTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 651 2010Maja Teli, man Prtenjak Abstract The interaction of a summer frontal bora and the sea-land breeze along the north-eastern Adriatic coast was investigated by means of numerical simulations and available observations. Available measurements (in situ, radiosonde, satellite images) provided model validation. The modelled wind field revealed several regions where the summer bora (weaker than 6 m s,1) allowed sea-breeze development: in the western parts of the Istrian peninsula and Rijeka Bay and along the north-western coast of the island of Rab. Along the western Istrian coast, the position of the narrow convergence zone that formed depended greatly on the balance between the bora jets northward and southward of Istria. In the case of a strong northern (Trieste) bora jet, the westerly Istrian onshore flow presented the superposition of the dominant swirled bora flow and local weak thermal flow. It collided then with the easterly bora flow within the zone. With weakening of the Trieste bora jet, the convergence zone was a result of the pure westerly sea breeze and the easterly bora wind. In general, during a bora event, sea breezes were somewhat later and shorter, with limited horizontal extent. The spatial position of the convergence zone caused by the bora and sea-breeze collision was strongly curved. The orientation of the head (of the thermally-induced flow) was more in the vertical causing larger horizontal pressure gradients and stronger daytime maximum wind speed than in undisturbed conditions. Except for the island of Rab, other lee-side islands in the area investigated did not provide favourable conditions for the sea-breeze formation. Within a bora wake near the island of Krk, onshore flow occurred as well, although not as a sea-breeze flow, but as the bottom branch of the lee rotor that was associated with the hydraulic jump-like feature in the lee of the Velika Kapela Mountain. Copyright © 2010 Royal Meteorological Society [source] Dynamics of jet streaks in a stratified quasi-geostrophic atmosphere: Steady-state representationsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 600 2004Philip Cunningham Abstract The structure and dynamics of jet streaks in the extratropical upper troposphere are examined in the context of a continuously stratified quasi-geostrophic (QG) framework. It is hypothesized that jet streaks may result from the superposition of monopolar or dipolar vortices of mesoscale dimensions with the enhanced potential-vorticity gradients constituting the tropopause. Based on this hypothesis, steady-state monopolar and dipolar vortices in a uniform zonal background flow on an f -plane are investigated for their applicability as idealized dynamical representations of jet streaks. The representations of jet streaks satisfy the nonlinear governing equations of the continuously stratified QG framework: the monopolar vortex is specified in terms of axisymmetric distributions of QG potential vorticity in the interior of the domain and perturbation potential temperature on upper (tropopause) and lower (surface) boundaries, whereas the dipolar vortex is adapted from a closed-form analytical solution for the geostrophic stream function. Through the incorporation of vertical structure and divergent circulations, these representations of jet streaks extend those presented previously by the authors using a non-divergent barotropic model. It is shown that these vortex representations display characteristic signatures similar to those observed in atmospheric jet streaks. In particular, both the monopole and the dipole exhibit an ageostrophic wind directed towards lower geopotential height in the entrance region of the streak and towards higher geopotential height in the exit region. For the monopole, this ageostrophic wind is entirely rotational and there is no vertical motion. For the dipole, the rotational part of the ageostrophic wind dominates the divergent part; the latter is associated with a four-cell pattern of vertical velocity similar to that described in conceptual models of straight jet streaks. For both the monopole and the dipole, the jet streak is induced by the vortex structure such that the wind speed maximum translates at the same speed as the individual vortices; this translation speed is slower than the maximum wind speed in the core of the speed maximum, consistent with observations of jet streaks. It is proposed that the above representations provide a formal theoretical foundation for the conceptual models of jet streaks prevalent in the literature; these conceptual models typically are based on heuristic kinematic or parcel arguments and not on consistent solutions to a physically plausible set of equations. The representations also provide a foundation upon which to explore the unsteady behaviour of jet streaks in terms of the superposition of monopolar and dipolar vortices with non-uniform zonal background flows. Copyright © 2004 Royal Meteorological Society. [source] | ||||||||||