Teacher Recruitment and Selection during the Period 1944 through 1947

Eliassen, Reuben H.; Martin, Robert L.

doi:10.1080/00220671.1948.10881641

Cited by 4 publications

(1 citation statement)

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“…We assume that the motion perturbing this flow occurs on such a scale that the change in the velocity vector of parcels is small compared with the acceleration imposed by the uniformly rotating frame of reference. This assumption leads to the geostrophic momentum approximation originally proposed by Eliassen (1948).…”

Section: Summary Of Mathematical Formulationmentioning

confidence: 99%

Warm and occluded fronts in two‐dimensional moist baroclinic instability

Joly

Thorpe

1989

Quart J Royal Meteoro Soc

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SWARYThe two-dimensional Eady mode of baroclinic instability exhibits a strong cold front structure after a period of development using semi-geostrophic equations excluding moist processes. Indeed the surface wave has a single centre of cyclonic vorticity on the cold side of the warm air anomaly. Here results are presented from a semi-geostrophic numerical model including moist effects which predicts an Eady wave with a cold and a warm front associated with two centres of surface vorticity located on either side of the warm anomaly. The ascent regions are taken to be saturated and close to moist neutral which in this baroclinic environment corresponds to a condition of zero equivalent potential vorticity; the descent is taken to be unsaturated.This development of a structure resembling a warm front occurs only when the moist effects become dominant within a pre-existing, weak, dry Eady mode. Using the same condensation representation starting from an extremely small, and random, amplitude disturbance a 'pure' moist Eady mode develops with a single vorticity maximum in the form of a cold front. In nature it is likely that often the moisture becomes dominant after a period, albeit sometimes a short period, of essentially unsaturated growth, although observational evidence is limited. Therefore the process of warm frontogenesis described here may be a contributory factor to those minority of mid-latitude cyclones which exhibit a strong warm front. The model indicates that the warm front moves more slowly than the cold front, resulting in a cold occlusion process.These investigations require a detailed examination of the initial growth of small amplitude disturbances near the limit of neutral moist ascent, i.e. pure moist modes. Results of previous such calculations using an analytical 2-level model are confirmed here using a numerical multi-level model. The more accurate estimates obtained here show that the finite growth rate in the limit of zero equivalent potential vorticity has a value of 1.9 times the dry value compared with the 2-4-fold increase given by the 2-level model.

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Section: Summary Of Mathematical Formulationmentioning

confidence: 99%