Podcast #128: We chat with Kent C Dodds about why he loves React and discuss what life was like in the dark days before Git. Listen now.

Hot answers tagged

24

Tornadoes are the result of small-scale effects such as the convergence of updraft/downdraft regions in a single thunderstorm, the stretching or entrainment of vertical vorticity, wind shear profiles, and even friction with the ground. Hurricanes rely on massive amounts of latent heat release from an atmosphere moistened by warm ocean waters causing rising ...


23

The short answer is yes, it's possible. And it can also reduce harm. Summary of the changes Here's a brief summary of the changes that happen when electricity is generated from a wind turbine, rather than from a fossil or nuclear plant: energy is taken out of the wind further upwind than it would otherwise be there is more turbulence just downwind from ...


18

Wind is caused by pressure differences. Think of a balloon full of air; poke a hole in it and the air comes out. Why? Because the pressure in the balloon is higher than outside, and so to regain equal pressure, mass moves and that is the wind. There is a bit more to this in the atmosphere as the Earth rotates and near the surface friction also plays a ...


17

To my knowledge, the best study looking at potential explanations for the Red Sea crossing is the one by Nof and Paldor (1992). They present a couple of plausible scenarios for the crossing. The main one is the effect of strong winds blowing along the Gulf of Suez and they find that the sea level drop could be sufficient: It is found that, even for ...


15

It's partly historical, partly point-of-view, but it's not a mistake. The friction coefficient emphasises the effect of the surface on a property of the boundary layer, i.e., greater surface friction slows the near-surface wind more. Aerodynamic resistance emphasises the effect of the boundary layer on surface-atmosphere exchange, i.e., greater mixing ...


14

Your uwnd variable holds 32 bit floats and has shape (1,73,144) corresponding to time, lat, lon and is located in the Dataset you have called 'U'. One way to put this in a numpy array is: uwind = np.zeros((lat,lon), np.float) uwind = U.variables['uwnd'][1,:,:] The first line sets the size of the uwind array, which is helpful from a performance standpoint ...


13

On a broader scale the ITCZ and monsoons are related. This is because the global circulation shifts as a result of the tilt of the earth's axis relative to the orbit around the sun. In northern hemisphere summer, the northern hemisphere is tilted towards the sun and receives more radiation (energy) than the southern, and vice versa for northern winter, The ...


13

Ageostrophic winds are merely the component of the actual wind that is not geostrophic. In other words, given the actual wind ($\mathbf v$) and the geostrophic wind ($\mathbf v_g$), the ageostrophic wind ($\mathbf v_a$) is the vector difference between them. The ageostrophic wind represents friction and and other effects. This, for example, is responsible ...


12

Before defining wind velocity, I think it is necessary to explain the continuum assumption. The basic idea is that even though gases are composed of discrete molecules occupying a small fraction of the total volume filled by the gas, gas flows are made up of many individual collisions between gas molecules. In most applications, the flow field is assumed to ...


12

Yes, it is real. Whoever took the photo, congratulations on a very fine image. I have never seen this texture on such a scale, but something similar can be achieved in the laboratory by creating a bubble membrane of pure super-cooled water and blowing a few dust nuclei onto the surface. A comparable geometry appears very rapidly. The size of the ice crystals ...


12

Hurricanes can be viewed as having primary and secondary circulations. The primary circulation is what we see in satellite photos, comprising the winds and clouds that circle the low pressure zone at the center of the hurricane. The secondary circulation is a vast heat engine that provides the energy needed to sustain the primary circulation. The low ...


11

The phenomenon you describe is denoted as a land breeze. It is caused by a difference between the sea surface temperature and the land surface temperature. Surface Temperature During day time the surface temperature at land rises faster than the sea surface temperature, whereas during night time the land surface cools faster than the sea surfaces. As a ...


10

You can calibrate anemometers from other anemometers, or loosely from a windsock if precision isn't that important. But per your question, how was the first anemometer calibrated? See my answer about wind and you'll see that we have equations that relate fluid velocity to factors like pressure gradients, friction, coriolis force, advection, etc. We could ...


10

The winds in a hurricane move cyclonic and inward at the surface and anti-cyclonic and outward in the upper troposphere. Cyclonic winds are counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere. Anti-cyclonic is the opposite of cyclonic. See this answer for a more detailed discussion of the winds within a tropical cyclone.


10

This is a good question, and the answer is, aerodynamic resistance is not defined inversely. It is rather, defined in a context that is often misinterpreted. In your question, you state that aerodynamic resistance is basically how much the roughness of the surface slows air movement down. This statement is not correct, and it seems to stem from the ...


10

Omega, ω is closely related to w in meteorology. It can be moved towards w using the chain (this reminder from Watkins at SJSU helped)... ω = dp/dt = (dp/dz)(dz/dt) = (dp/dz)w [where p is pressure, t is time, z is height, and w is vertical motion in height coordinates] Often in general meteorology you can estimate dp/dz using the hydrostatic ...


10

Looks like Cirrus Fibratus (Ci fib) to me. See e.g. Wolkenatlas or Clouds Online. Regarding the formation of Ci fib, Name of Clouds says: Cirrus fibratus clouds are formed when winds at high altitudes are strong and flow over the cold air from below. The combination of the warm air and the moisture is usually unevenly distributed hence the trail of fine ...


9

Kinetic energy is the work needed to accelerate a mass. Wind defined as the velocity air (not the same as energy, as noted in comment). However, the air moved by wind is a good example of kinetic energy, molecules are accelerated by a difference in pressure and moved. When the pressure difference decreases, the movement of molecules stop. So yes, the wind ...


9

By way of analogy consider a hot air balloon. The balloon encloses some air. As the air is heated, via massive gas burners, the air in the balloon becomes less dense compared to the air outside the balloon and eventually the less dense air in the balloon rises, lifting the balloon into the air. Atmospheric air in contact with the Earth does the same thing. ...


9

The key text here is "for $z>z_0$". It's telling you that, while you can evaluate the equation for other values of $z$, outside of that range the equation is not a valid description of the physical system. The equation could be written piece-wise to be complete: $u(z) = \begin{cases} (u_*/k) \ln(z/z_0)& z>z_0 \\ 0 & z\le z_0\end{cases}$ But ...


9

This picture was taken in what seem to be a small pond, of very calm water. It seem that in ideal conditions, implying but not limited to : absence of winds clean water eg: no nuclei to provide an anchor for crystal formation low temperature gradient between air and watrer (air almost near 0 °C and very slowly falling) ice grain can grow quite large. This ...


8

The first problem to tackle is "what is an odor"? An odor is a chemical aerosol or gas, which are small molecules suspended in the atmosphere. To track the odors of pizza or burning wood you would first need to identify the molecules associated with the scent. One example is α-pinene, which is the molecule that gives pine trees their scent. Food cooking ...


8

The way I understand it is the height above the surface at which buoyant (heat) production of turbulence first equals the mechanical (shear) production of turbulence. A more useful definition is given by the American Meteorological Society: A parameter with dimension of length that gives a relation between parameters characterizing dynamic, thermal, and ...


8

First some definitions: $z_0$: Roughness length is defined as the height at which the mean velocity is zero due to substrate roughness. Real walls/ground are not smooth and often have varying degrees of roughness, this parameter (which is determined empirically) accounts for that effect. $d$: Zero Plane displacement is defined as the height at which the ...


8

A very good analysis looking at the 3% relationship is an article by Weber (1983). His main result is that: We assume a fully developed sea, and take the eddy viscosity to be proportional to the friction velocity times a characteristic depth. Hence the total current (Ekman current plus wave-induced current) can be expressed as functions of the wind speed....


8

I wouldn't say water is naturally cooler than air. What I would say is that water has a higher heat capacity than air. This means it takes more energy to affect the same increase in temperature and conversely it takes water longer to cool down than air. You can see this at night near bodies of water when the sea breeze changes to a land breeze as the land ...


8

This has been tried to some extent; Strata in London was a skyscraper that was built with three wind turbines at the top, with a deliberate design to funnel wind into them. There are other examples. Siting renewable energy generation in cities is very attractive, partly because many people feel that the "industrial" feel fits better there, but also because ...


8

Weather stations and airports around the world almost always include an anemometer. Because of ground friction, the wind speed varies with height, so instrumental deployment is set at a standard height of 10 metres in open rural areas. This may require some adjustment in urban or forested areas. In fact, measuring accurate wind speeds above tree canopies is ...


7

The surface temperature is the temperature of the air at the surface (rather than the temperature of the ground itself). This temperature is typically taken between 1 and 2 m off the ground, and this is the temperature we feel when we are outside. Simply put, the reason air affects this temperature, sometimes radically, is because temperature is a property ...


7

Taming hurricanes with arrays of offshore wind turbines Nature Climate Change 4, 195–200 (2014) It finds that large turbine arrays (300+ GW installed capacity) may diminish peak near-surface hurricane wind speeds by 25–41 m s−1 (56–92 mph) and storm surge by 6–79%. In the case of offshore turbine arrays in particular locations there is potential benefit ...


Only top voted, non community-wiki answers of a minimum length are eligible