Status Updates From Atmospheric Science: An Int...

Just as in the Carnot cycle, heat is added at a high temp (in the lower troposphere) and rejected at a lower temp (higher in the troposphere)

The efficiency (eta) of the atmosphere is quite low bc the difference between the mean added and rejected temps (T1 and T2) is only a few degrees

⚠️⚡️⚠️ atmospheric motions transport E poleward and upward from a WARM SOURCE to a SLIGHTLY COLDER SINK

⚠️⚡️⚠️ In a statistical sense, the SOURCES of energy for the atmosphere are located at relatively low latitudes and low elevation, while the SINKS of energy are located at somewhat higher latitudes and higher levels where the temps are somewhat lower

The total area under the curves (avg’d net solar radiation) are identical but the SHAPES of the two curves are different. The net solar radiation (1-A)S/4 drops off by that factor of 4 between the equator and the poles. This strong latitudinal gradient is largely bc the SHARP DECREASE IN INSOLATION W LATITUDE during the winter season and the large local albedo that prevails in polar regions (icecaps+summer clouds)

Thermally driven = the wind field bears a direct relation to the horizontal heating pattern

⚠️✈️ Waves like the Kelvin-Helmholtz ones are often present within laters of moderate and severe clear air turbulence. The motions that produce the bumpiness are NOT the waves themselves, but the smaller-scale motions that RESULT FROM THEIR BREAKDOWN

Richardson number (Ri) = ratio of the work done against gravity by the vertical motions in the waves to the KE available in the shear flow

The smaller the value of Ri, the less stable the flow wrt shear instability

Most commonly accepted value for the onset of shear instability is Ri = 0.25. Once turbulence is established in a shear layer, it should be sustained so long as Ri is less than or equal to 1

In general, the larger the static stability the larger the critical shear

⚠️✈️⚠️ the relative ineffectiveness of the energy cascade mechanism in dissipating large-scale motions is due to the fact that such motions accomplish most of their transfer of E to smaller scales ONLY WITHIN CERTAIN VERY LIMITED REGIONS of the atmos

These regions = discrete patches or layers of clean air turbulence (CAT) = regions of bumpiness due to presence of vigorous small-scale motions in lowest km

⚠️⚠️ baroclinic waves form in regions of STRONG VERTICAL WIND SHEAR

⚠️ For baroclinic disturbances to amplify most rapidly, the slope of air trajectories should be about half as steep as the isentropes

The warm core of a hurricane serves as a reservoir of PE, which is continuously being converted into KE by a strong thermally DIRECT circulation with the rising of warm air near the center of the storm and the sinking of the cooler air outside

🏝️We’re forced to conclude that the local circulations over desert regions during summer are of the thermally INDIRECT type, driven, not by local heating contrasts, but by a xontinual input of KE from other regions of the tropics

It’s not obvious why the atmos should choose to use up part of the KE generated in thermally DIRECT circulations in one region to create a desert in another, but it is what it is

⚠️🏝️⚠️ extreme warmth and dryness of desert regions during summer is the result of large-scale subsidence which heats rhe air by adiabatic compression and lowers its RH to the point where cumulus convection is almost entirely supressed

⚠️ Hadley circ = meridional overturning (features air rising near the equator, flowing poleward near the tropopause, cooling and descending in the subtropics at around 30deg lat, and then returning equatorward near the surface)
Bc the earth’s rotation, the Hadley circulation gives rise to lower tropospheric easterlies (the trade winds) and upper tropospheric westerlies in the zonal and time average circulation

“Wet monsoons” = rising motion over the warm land masses

Available PE generated by the differential heating between land and sea is released by the warm (light) air and the sinking of cold (dense) air

The more reversible the motions, the larger the fraction of the original potential energy that is actually converted into kinetic energy

Monsoons = atmospheric response to land-sea heating contrasts, and a large-scale meridional overturning over the mid Atlantic and Pacific Oceans which gives rise to the intertropical convergence zone, a narrow east-west band of heavy cloudiness and precip

The distinguishing characteristic of a baroclinic atmosphere is the existence of regions in which the height and thickness contours intersect one another at since angle so that the geostrophic wind has a component normal to the isotherms (or thickness contours)

In a barotropic atmosphere there is no vertical shear of the geographic wind

⚠️ concepts of geostrophic and gradient wind have meaning ONLY in LARGE-SCALE atmospheric motions.

Earth’s rotation plays only a very MINOR ROLE in the dynamics of CONVECTIVE-SCALE motions

⚠️ if streamlines are mistakenly used in place of trajectories the resulting centrifugal force term is almost certain to be INCORRECT and might even be the WRONG SIGN

⚠️ ^ gradient wind = the 3-way balance of Coriolis, PGF, centrifugal force

⚠️ sharp troughs and tight pressure gradients are more common than sharp ridges with tight pressure gradients, bc it is NOT POSSIBLE to achieve a 3-way balance of Coriolis, PGF, and centrifugal in the sharp anticyclone+strong PG combo
⚠️ for the cyclonic case, the centrifugal force REINFORCES the Coriolis force st the 3-way balance CAN be achieved with a wind velocity smaller than if Coriolis was acting alone

Subgeostrophic winds (not enough Coriolis) is analogous to a train coasting along a sloping surface. In the absence of friction, the train could maintain constant speed on a track that follows along a constant height contour. In reality where there is friction, its possible to coast at constant speed only along a track that drifts steadily downhill at some angle relative to the contours (hor PGF = push air H to L p)

The tighter the spacing of isobars or geopotential height contours, the stronger the Coriolis force that is required to balance the pressure gradient force, and therefore, the stronger the geostrophic wind

⚠️☀️☀️⚠️ the freq of solar activity os modulated by the 11-year solar cycle. During maxima years (like 1958) sunspots, faculae, and flares are numerous. During minima (like1964) solar activity practically disappears.

Talked about this today (1/28) in Intro to Climate

⚠️ f = Coriolis parameter = 2(omega)sin(phi)

+f in NH
-f in SH

f = 10^(-4) s^(-1) in middle latitudes

⚠️ Coriolis is directed toward the RIGHT of the velocity vector in the NORTHern hemisphere + toward the LEFT in the SH

⚠️⚠️ omega = vertical velocity
pos omega = sinking motion
omega ~= -w(p/H) (H=scale height)

w = vertical velocity component (terms of height) = dZ/dt