Related Experiment Video
Updated: Jun 9, 2026
13:27
Exploring the Effects of Atmospheric Forcings on Evaporation: Experimental Integration of the Atmospheric Boundary Layer and Shallow Subsurface
Published on: June 8, 2015
Reduced drag coefficient for high wind speeds in tropical cyclones
Mark D Powell1, Peter J Vickery, Timothy A Reinhold
1National Oceanic and Atmospheric Administration, Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division, Miami, Florida 33149, USA. Mark.Powell@noaa.gov
Nature
|March 21, 2003
Summary
Momentum transfer between ocean and atmosphere under extreme winds shows surface flux leveling off, contrary to current models. This finding impacts hurricane prediction and risk assessment.
Area of Science:
- Atmospheric science
- Oceanography
- Geophysics
Background:
- Atmospheric-ocean momentum transfer is key for weather and climate.
- Direct measurements are limited to low wind speeds, necessitating extrapolation for extreme conditions.
- Tropical cyclones present unique challenges for understanding marine boundary layer dynamics.
Purpose of the Study:
- To analyze wind profiles and momentum transfer in tropical cyclones using GPS sonde data.
- To investigate surface momentum flux behavior under hurricane-force winds.
- To compare findings with existing surface flux parameterizations used in climate models.
Main Methods:
- Utilized Global Positioning System (GPS) sondes to measure wind speed profiles in the marine boundary layer.
- Analyzed data from 1997 onwards, focusing on tropical cyclone conditions.
- Determined surface stress, roughness length, and neutral stability drag coefficient.
Main Results:
- Observed a logarithmic increase in wind speed with height up to 200 m.
- Identified maximum wind speeds at 500 m, with gradual weakening up to 3 km.
- Found that surface momentum flux levels off at wind speeds exceeding hurricane force.
Conclusions:
- Current surface flux parameterizations used in climate and risk assessment models may be inaccurate for extreme wind conditions.
- The leveling off of momentum flux challenges existing models of atmospheric-ocean interaction.
- This research provides crucial data for improving hurricane modeling and prediction accuracy.
Related Concept Videos
01:18Drag Force and Terminal Speed
An interesting force in everyday life is the force of drag on an object when it is moving in a fluid. Like friction, the drag force always opposes the motion of an object. Unlike simple friction, the drag force is proportional to some function of the velocity of the object in that fluid. This functionality is complicated and depends upon the shape of the object, its size, its velocity, and the fluid it is in. For most large objects, such as cyclists, cars, and baseballs, that are not moving too...
01:23Coriolis Force
An accelerating particle experiences a force equal to the mass multiplied by the acceleration in an inertial frame of reference. Consider a particle in a non-inertial frame of reference, such as a sliding ball on a rotating table. The acceleration of the ball in this rotating reference frame is different than in the intertial frame, which modifies its equation of motion. The fictitious forces acting additionally on a rotating frame of reference alter Newton's Second Law expression. Centripetal...
01:11Velocity and Acceleration in Steady and Unsteady Flow
In fluid mechanics, velocity and acceleration are key concepts for analyzing particle motion in both steady and unsteady flow. Consider a fluid particle moving along a pathline, where its velocity depends on its position and time. The particle's acceleration is obtained by differentiating the velocity with respect to time.
The acceleration can be generalized to any point in the flow, and expressed as components along three perpendicular directions, representing changes in velocity over time.
The acceleration can be generalized to any point in the flow, and expressed as components along three perpendicular directions, representing changes in velocity over time.
01:24Turbulent Flow
Turbulent flow is characterized by unpredictable fluctuations in velocity and pressure, which result in a chaotic fluid movement distinct from the orderly patterns of laminar flow. While laminar flow is governed by smooth, parallel layers with minimal mixing, turbulent flow exhibits highly irregular, three-dimensional patterns. This behavior arises due to instabilities in the fluid's velocity profile, and amplifies as the flow velocity increases. Minor disturbances, known as turbulent spots,...
01:18Boundary Layer Characteristics
When a fluid encounters a solid surface, a boundary layer forms due to the interaction between the fluid's motion and the stationary surface. This phenomenon is characterized by a thin region adjacent to the surface where viscous forces dominate, influencing the fluid's velocity profile. The development of the boundary layer begins at the leading edge of the surface and evolves as the fluid moves downstream.As the fluid flows over the surface, friction between the fluid and the wall slows down...
01:17Design Example: Calculating Safe Diameter for Wind-Exposed Disc
Assessing safety in wind-exposed installations is crucial to preventing potential failures. This example explores the calculation and design adjustments needed to mount a circular disc on a building facade, where wind forces are a primary concern. A 4-meter diameter disc was initially designed as an aesthetic feature facing winds at a velocity of 25 meters per second, with an air density of 1.25 kilograms per cubic meter. Given these conditions, the drag force on the disc was determined using...