Diagnosis of Ageostrophic Circulations in a Two-Dimensional Primitive Equation Model of Frontogenesis

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Abstract
Diagnoses are presented of the transverse ageostrophic circulation patterns for two cases from a two-dimensional primitive equation model of frontogenesis forced by a combination of confluence and horizontal shear. The cold advection case (the specified alongfront potential temperature gradient results in differential cold advection by the upper-level jet) realistically simulates upper-level frontogenesis in response to tilting by a cross-front gradient of subsidence. The warm advection case features a frontal system spanning the troposphere, which develops in response to differential horizontal advection. The diagnoses are performed by numerically solving three versions of the two-dimensional Sawyer–Eliassen equation for the streamfunction of the transverse ageostrophic circulation. The quasi-geostrophic (QG) and geostrophic momentum (GM) versions are based on the approximation of cross-front geostrophic balance, while the primitive equation (PE) version includes the possibility of an alongfront... Abstract Diagnoses are presented of the transverse ageostrophic circulation patterns for two cases from a two-dimensional primitive equation model of frontogenesis forced by a combination of confluence and horizontal shear. The cold advection case (the specified alongfront potential temperature gradient results in differential cold advection by the upper-level jet) realistically simulates upper-level frontogenesis in response to tilting by a cross-front gradient of subsidence. The warm advection case features a frontal system spanning the troposphere, which develops in response to differential horizontal advection. The diagnoses are performed by numerically solving three versions of the two-dimensional Sawyer–Eliassen equation for the streamfunction of the transverse ageostrophic circulation. The quasi-geostrophic (QG) and geostrophic momentum (GM) versions are based on the approximation of cross-front geostrophic balance, while the primitive equation (PE) version includes the possibility of an alongfront...

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