4.1 Gravity waves in moist baroclinic jet-front systems: characterization, dynamics, and their impacts on momentum transport, convective initiation/modulation, and mesoscale predictability (INVITED)

Monday, 3 August 2015: 4:00 PM
Republic Ballroom AB (Sheraton Boston )
Fuqing Zhang, Pennsylvania State Univ., Univ. Park, PA; and J. Wei and Y. Sun

This first part of the presentation introduces a series of high-resolution cloud-permitting simulations of idealized moist baroclinic waves that are performed to study gravity waves among moist baroclinic jet-front systems with varying degree of convective instability, to examine the similarities and differences of wave characteristics, initiations and propagations among different simulations, and to understand the coupling and interactions of gravity waves with small-scale moist convection and large-scale background baroclinic waves. A 4-D linear ray-tracing analysis and a 2-D spectral decomposition are further used to investigate the source mechanisms, propagating characteristics, life cycles of these waves, along with the assessment of the wave-induced momentum fluxes and their impacts on the large-scale circulation.

The second part of the talk will discuss the impacts of moist convection and gravity waves on the error growth dynamics and the limit of predictability for mesoscale processes within idealized baroclinic waves of varying convective instability. In the dry experiment free of moist convection, error growth is controlled solely by baroclinic instability under which the scale and amplitude of the initial condition error is inversely correlated with the limit of the predictability of the baroclinic system. This is not the case under the impact of moist convection. For perturbation with small amplitude, forecast error is characterized by strong upscale growth from convective instability. This upscale growth is only weakly sensitive to the scale and amplitude of the initial perturbations, which imposes a finite-time barrier to forecast accuracy and thereby the intrinsic predictability of the system. Gravity waves and geostrophic adjustment may play an important role in the upscale error growth from moist convection that ultimately limits the predictability of mesoscale processes as well as the parent large-scale baroclinic waves.

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