CLIMATE/EARTH 401�Geophysical Fluid Dynamics�Dynamical Meteorology
Thermal Wind: Interpretation
Geostrophic wind
Links horizontal temperature gradient
with vertical wind gradient.
Take p, height, derivative
Zonal mean structure of atmosphere
Zonal mean temperature - Jan
north (winter)
south (summer)
approximate tropopause
Zonal mean temperature - Jan
north (winter)
south (summer)
∂T/∂y ?
Zonal mean temperature - Jan
north (winter)
south (summer)
∂T/∂y ?
<0
<0
<0
>0
<0
<0
Zonal mean temperature - Jan
north (winter)
south (summer)
∂T/∂y ?
<0
<0
<0
>0
<0
<0
> 0
<0
<0
>0
>0
>0
∂ug/∂p ?
Zonal mean wind - Jan
north (winter)
south (summer)
Idealized jet: Wind and Temperature
In class problem
Refer to the figure. This figure shows a jet stream in the northern hemisphere, upper troposphere. The direction is easterly, from the east. We saw that in a hydrostatic atmosphere the vertical gradient of the geostrophic wind, was related to the horizontal gradient of temperature. That is the thermal wind relationship. What is the sign of the vertical gradient of the wind below the jet stream? With this information, is point A warmer or colder than point B ? Where are the temperature gradients strongest ? Be sure to justify your decisions.
Thermal wind
In class problem
y, north
- p, vertical
-10 m/s
-20 m/s
-30 m/s
-5 m/s
A
B
In class problem
y, north
- p, vertical
-10 m/s
-20 m/s
-30 m/s
-5 m/s
Between lower and upper point Δu is < 0,
Δp < 0, hence vertical gradient in p coordinates is positive.
What is the sign of the vertical gradient of the wind below the jet stream?
A
B
In class problem�(pressure coordinates)
With this information, is point A warmer or colder than point B?
In class problem�(Height Coordinates)
With this information, is point A warmer or colder than point B?
In class problem
y, north
- p, vertical
-10 m/s
-20 m/s
-30 m/s
-5 m/s
A, cooler
B, warmer
With this information, is point A warmer or colder than point B?
In class problem
y, north
- p, vertical
-10 m/s
-20 m/s
-30 m/s
-5 m/s
A, cooler
5) Where are the temperature gradients strongest?
B, warmer
Strong shear.
In class problem
y, north
- p, vertical
-10 m/s
-20 m/s
-30 m/s
-5 m/s
A, cooler
Strong temperature gradient.
5) Where are the temperature gradients strongest?
B, warmer
Weather maps: Real situation
Schematic of thermal wind.
Low pressure systems marked on map
850 hPa surface
300 hPa surface
X
X
X
Low pressure systems marked on map
850 hPa surface
300 hPa surface
X
X
X
Geostrophic wind marked on map
850 hPa surface
300 hPa surface
Geostrophic wind marked on map
850 hPa surface
300 hPa surface
Relation between zonal mean temperature and wind is strong
End: Thermal Wind: Derivation