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Evaluation of physical processes in an idealized extratropical cyclone using adjoint sensitivity
Author(s) -
Langland Rolf H.,
Elsberry Russell L.,
Errico Ronald M.
Publication year - 1995
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49712152608
Subject(s) - baroclinity , extratropical cyclone , troposphere , cyclone (programming language) , advection , environmental science , cyclogenesis , climatology , atmospheric sciences , tropical cyclone , sensitivity (control systems) , sea surface temperature , tropical cyclogenesis , meteorology , geology , physics , field programmable gate array , electronic engineering , computer science , computer hardware , engineering , thermodynamics
An adjoint model is used to examine the sensitivity of an idealized dry extratropical cyclogenesis simulation to perturbations of predictive variables and parameters during the cyclone life cycle. the adjoint sensitivity indicates how small perturbations of model variables or parameters anywhere in the model domain can influence cyclone central pressure. Largest sensitivity for both temperature and wind perturbations is located between 600 and 900 hPa in the baroclinic zone above the developing cyclone. Perturbations of a given size have more influence on cyclone intensity when located in high‐sensitivity regions (the middle and lower troposphere in this simulation). the effects of physical processes can be interpreted with adjoint sensitivity by considering perturbations that are proportional to temperature and wind tendencies in the basic state (nonlinear forecast). In the early phase of the cyclone life cycle, temperature advection near the steering level in the lower troposphere (about 800 hPa) is strongly cyclogenetic and resembles a Charney mode of baroclinic instability. During the phase of most rapid deepening, temperature advection in the lower troposphere remains important, while interpretation of sensitivity to wind perturbations suggests that increased vorticity in the middle and upper troposphere above the surface low‐pressure centre may also be significant for cyclone intensification. Adjoint techniques can provide insight into spatial and temporal sensitivity not easily obtained from other methods. Higher sea surface temperature (SST) has a cyclogenetic effect mainly in a localized region corresponding to the cyclone warm sector. Outside the areas of high sensitivity, small perturbations of SST have very little effect on central pressure of the forecast cyclone. When strong upward sensible‐heat flux, F s , exists, it can have a cyclogenetic (preconditioning) influence early in the cyclone life cycle, although downward F s in the cyclone warm sector is anticyclogenetic during the phase of most rapid deepening. the sensitivity indicates that F s can be cyclogenetic in one location and anticyclogenetic at the same time in another location, so that F s effects on cyclone intensity are partially self‐cancelling. Surface momentum stress is anticyclogenetic, with sensitivity highly localized in the cyclone warm sector.