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# Global Circulation

### Stull Chapter 11

Question | Answer |
---|---|

Radiative Differential Heating | Net radiative heating in tropics and net radiative cooling at poles creates and imbalance in the atmosphere/ocean system. |

Thermal Wind Relationship | The relationship between horizontal and vertical temperature gradient of geostrophic wind. dUg/dz=(-g/Tvfc)(dTv/dy) dVg/dz=(g/Tvfc)(dTv/dx) The north-south temperature gradient alters the east-weest geostrophic winds with height, and vice versa. |

Thermal Wind Components | UTH=Ug2-Ug1=-(g/fc)(dTH/dy) VTH=Vg2-Vg1=(g/fc)(dTH/dx) *Implies that the thermal wind is parallel to the thickness contours (cold temps to left in N hemisphere). |

What is the Thermal Wind? | The vector difference between geostrophic winds at two different heights or pressures. |

Troposphere Trends | The tropopause is lower near poles than near equator. Causing the air over the equator to be colder and warmer over the poles in the stratosphere. |

Thickness vs. Isobars | Greater TH btwn P sfcs in warmer equatorial air than colder polar air causes isobars to become more tilted at mid-latitudes as tropopause is approached. Regions with greatest tilt have greatest S-N P gradient -- drives fastest geostrophic wind. |

Jet Stream | Fast geostrophic wind occurs in region greatest S-N P gradient; @ tropopause in mid-lat; move N in summer, S in winter. Velocity +, E-W, in N/S hemis. Mark boundary btwn cold air & warm air b/c T dif generates jet stream winds (thermal wind relationship). |

Jet Stream Speeds | Actual average speeds of 40 m/s are observed over a three-month average in the winter hemisphere. Velocities up to 100 m/s can be observed on individual days. |

Angular Momentum- Theoretical | Eastward angular momentum conserved as it moves northward from a source latitude [phi]s to a destination [phi]d. |

Angular Momentum and the Earth | Radius - Earth's axis to [phi]: R[phi]=ReCos([phi]) Tangential velocity - Earth at [phi]: U[phi]=[omega]R[phi]=[omega]ReCos([phi]) Air parcel - source to dest., velocity relative to Earth: U'=[omega]Re((Cos([phi]s)^2/Cos([phi]d))-cos([phi]d)). |

Angular Momentum - Actual | Angular momentum is not conserved b/c P gradient, Coriolis, and turbulent drag forces act on the air. The actual vertical circulation pattern extends only to about 30 deg N and S (Hadley Cell). |

Relative Vorticity | A measure of the rotation of fluids about a vertical axis relative to Earth's sfc. Positive in counterclockwise direction. [Zeta]r=dV/dx-dU/dy [Zeta]r=-dM/dn+M/R If the fluid is rotating as a solid body, [Zeta]r=2M/R |

Absolute Vorticity | Measure with respect to "fixed" stars. Earth's rotation in addition to the relative vorticity. [Zeta]a=[Zeta]r+fc The Coriolis parameter is a measure of the vorticity of the planet. |

Potential Vorticity | Absolute vorticity divided by depth of rotating column of air. [Zeta]p=([Zetar]r+fc)/dz=constant Conserved in the absence of turbulent drag and heating. |

Vorticities Combined | If rotating column of air is stretched vertically, then relative vorticity must increase or move further N where planetary vorticity is greater. Relative={Shear={-dM/dn} Curvature={M/R}} Planetary={fc} Stretching={[Zeta]p(dz)} -dM/dn+M/R+fc=[Zeta]p(dz |

Planetary Waves | The jet stream meanders N and S in a wavy pattern due to instabilities in the atmosphere as they circle the globe. average wavelength of 3000 km to 4000 km. |

Created by:
lawli