On 30 October 2004 during a strong solar proton event, layers of enhanced backscatter from altitudes between 55 and 75 km have been observed by both ESRAD (52 MHz) and the EISCAT VHF (224 MHz) radars. These echoes have earlier been termed Polar Mesosphere Winter Echoes, PMWE. After considering the morphology of the layers and their relation to observed atmospheric waves, we conclude that the ra...

Simulation of scour-pit formations under the bridge decks and around the bridge piers, due to sediment suspension and transport caused by flooding and pressure flow conditions, is of significant interest nowadays to computational fluid dynamics (CFD) and hydraulic researchers. From CFD perspective, analysis of bridge under various flooding conditions and impact of the drag and lift forces on it...

A statistically stationary and nearly homogeneous turbulent shear flow is established by an additional volume forcing in combination with stress-free boundary conditions in the shear direction. Both turbulent energy and enstrophy are stationary to a much better approximation than in previous simulations that use remeshing. The temporal fluctuations decrease with increasing Reynolds number. Ener...

The potential for in situ turbulence to inhibit dinoflagellate population growth has been demonstrated by experimentally exposing dinoflagellate cultures to quantified shear flow. However, despite interest in understanding environmental factors that affect the growth of toxic dinoflagellates, little is known of the effect of shear on the growth of toxin-producing dinoflagellate species. Culture...

Modifications of turbulence regime in the sheared convective boundary layer (CBL) by a number of external nonbuoyant forcings are studied experimentally in a thermally stratified wind tunnel and numerically by means of large eddy simulation. This type of CBL is observed in the atmosphere when an originally neutral or stable air mass is advected over a heated underlying surface. Emphasis in the ...

The collapse of turbulence, observable in shear flows at low Reynolds numbers, raises the question if turbulence is generically of a transient nature or becomes sustained at some critical point. Recent data have led to conflicting views with the majority of studies supporting the model of turbulence turning into an attracting state. Here we present lifetime measurements of turbulence in pipe fl...

The copepod Acartia tonsa exhibits 2 different feeding modes: when feeding on small phytoplankton cells it sets up a feeding current and acts as a suspension feeder; when feeding on motile prey it acts as an ambush feeder. We examined experimentally the effects of small-scale turbulence on feeding rates in these 2 modes. The different feeding behaviours were triggered by offering the copepods d...

Computational experiments based on the direct numerical simulation of turbulent channel flow reveal that the skin friction can be reduced as much as 70% by the action of a localized steady force acting against the flow close to the wall. In addition, the excessive shear stresses observed during the laminar-to-turbulence transition can be substantially reduced. For a sustained reduction in the s...

Recent results and future challenges in the systematic analytical description of plasma turbulence are described. First, the importance of statistical realizability is stressed, and the development and successes of the Realizable Markovian Closure are briefly reviewed. Next, submarginal turbulence (linearly stable but nonlinearly self-sustained fluctuations) is considered and the relevance of n...

The deposition of energy into the solar wind beyond 1 AU is thought to result from the dissipation of low frequency magnetohydrodynamic (MHD) turbulence via kinetic processes at spatial scales comparable to the ion gyroradius. Beyond 1 AU, solar wind turbulence is comprised of both a decaying component generated in the corona and turbulence generated dynamically in situ by processes such as str...