11

Positive lightning is indeed very interesting. According to the National Weather Service, the reason why it has a higher amperage and voltage is due to the due to the amount of air it must get through to reach the ground. Otherwise, it would never reach the ground. Since it originates in the upper levels of a storm, the amount of air it must burn ...


10

This case is an excellent example of urban-induced convection. Urban areas have very different surface and soil properties, leading to a different heat balance relative to more natural environments. At times when solar shortwave radiation forcing is high - summer time, early afternoons - urban areas act as heat islands. Sensible heat flux and outgoing ...


10

First of all, the idea of a fixed "hotspot" reference frame is (albeit reluctantly) falling out of favour on a geological timescale; see e.g. http://onlinelibrary.wiley.com/doi/10.1029/GM121p0339/summary ("As studies of plate motions have advanced, however, it has become clear that the global hotspots do not stay fixed relative to each other...") and http://...


8

Magnetohydrodynamic experiments intended to create laboratory analogues for the Earth's magnetic field generally use molten sodium rather than nickel. You can read about the details of one such project, DRESDYN, in this arXiv preprint. The central part of the envisioned precession dynamo experiment… will be a cylindrical vessel of approximately 2 m ...


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

Is the mantle solid? It's all a matter of timescales. The mantle is undoubtedly solid (except locally in the uppermost regions where melting can occur) but on a long enough timescale it can display plastic behaviour under high temperatures and pressures, with a viscosity on the order of $\text{~}\mathrm{10^{21}~Pa~s}$ (based on estimates from isostatic ...


7

Lake breezes(similar to sea breezes) are fundamentally a feature of mesoscale meteorology and the peer reviewed reference Small Lake Daytime Breezes: Some Observational and Conceptual Evaluations details both the observational studies of lake breezes and the conceptual understanding behind the formation of the lake breeze. Since OP's question is How big ...


7

If you look closely at the diagram you'll notice height isn't the primary cause for the convergence between the adiabats, though it is the driver. Note that toward the upper right there is still appreciable difference between the adiabats and as you move to the left the height they converge at decreases. The reason for this, as your intuition suggests, ...


6

The mantle of Mars is heterogeneous. While there are many things that are unknown about the Martian mantle and the entire internal structure of Mars, this is not one of them. The source of this finding comes from the analysis of meteorites originating from Mars. Analysis shows that 4.5 billion years ago - when Mars was forming along with the rest of the ...


6

This is an interesting question and I feel the best answer is "a little bit of both". Consider your picture without the overshooting top and just the anvil. The tropopause is clearly defined as the anvil spreads out horizontally against the static stability of the stratosphere. Now let us consider a single parcel in the updraft, accelerating upward due ...


6

Humans have difficulty visualizing how rocks flow because the required conditions are outside our everyday experience. We are familiar with surface temperatures and pressures, and geologically short time-frames, where the distinction between solid and liquid is obvious. Under very high temperatures and pressures, and especially over longer time periods, ...


6

The Obukhov length ($L$) measures the relative importance of mechanical shear-generated turbulence and density-driven (buoyancy) fluxes (1) $L$ can be used to determine the eddy structure of the flow and it provides a measure for the hydrodynamic stability of the boundary layer - it effectively imposes an upper limit on the vertical excursion of fluid ...


5

If you're looking for a cool, well detailed map of convection cells that looks like a modern weather map....forget it. What you're looking for has been notoriously difficult to produce, if not impossible. Even the most advanced seismic tomography techniques using seismic wavespeeds can only resolve mantle "features" thousands of kilometers in scale, but ...


2

I'd like to add to the correct answers already given. Solids can flow and deform without being a liquid. You can bend iron bars. You can dent plastic. You can squeeze nylon bags. The cotton on your t-shirt bends as you move you hand. These are all solids. The ability of this to happen depends on temperature and pressure. Iron bars bend easier when heated. I'...


2

It is not clear that the Obukhov length has an exact physical interpretation. The length L is certainly a length that dimensional argument shows to follow from the set of basis parameters that Monin and Obukhov proposed was sufficient to describe turbulence in the bottom 10% or so of atmospheric boundary layers. We may ask several questions: is the MO basis ...


1

As already commented; a good indicator for rain in soundings is that the lower troposphere is saturated by water. Individual saturated levels would imply moisture, but if the moisture doesn't reach the surface then it maybe just clouds or rain that evaporates before reaching surface (virga). The deeper the saturated layer, the better indicator for rain it is....


1

From McKenzie's original 1984 paper and from Spiegelman & McKenzie (1987) paper the equations that govern the conservation of momentum and mass of a low-viscosity fluid melt (magma) in a deformable matrix (rocks) are: ${\partial\over\partial t} (\rho_f\phi) + \nabla \cdot (\rho_f\phi{\bf v})=\Gamma$ ${\partial\over\partial t} [\rho_s(1-\phi)] + \nabla \...


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