Thermal Wind Review (part II) 2.
3.
The isentropes are sloped downward towards the warmer temperatures in the troposphere. The theta values are higher at the equator and lower at the poles. Above the tropopause the isentropes slow downward towards the poles. This is because the warmer temps and higher theta values are located at the poles rather than the equator in the stratosphere. a.
∂T
∂y
below the jet would be negative since it would point toward the higher temperatures which would be located to the south. ∂T
∂y above the jet would b.
be positive since the gradient points towards the higher temperature now located to the north above the tropopause. This is the case since the wind becomes more westerly with height in the troposphere, which means the temperature gradient here must point south (according to eq. 1.44). The max wind speed is located at the tropopause. Above this the wind becomes more easterly (less westerly) with height, so that tells you the gradient must now point towards the north. The zones of negative meridional temperature gradients were generally located below the jet max, while the positive meridional temperature gradients were located above the jet max. This is in line with the thermal wind relation since the blue area below the jet max corresponded to increasing westerlies with height while the red area above the jet max corresponded to decreasing westerlies with height. 4.
5.
b. ∂T
∂y
would not make sense to look at in a N/S oriented jet stream. ∂T
∂y
is measures meridional temperature gradient. Since the jet is located along a strong temperature gradient, a N/S jet would be influenced by the zonal temperature gradient ∂T
∂x instead. 6.
The thermal wind is not an actual wind, it just tells us information about where the jet stream will be located. The thermal wind states that as long as warmer air is located to the south and colder air to the north, the wind speed will increase with height. Once you get above the troposphere, everything reverses and the wind speed actually decreases with height, therefore the jet stream is located at the top of the troposphere.