A189-0001
The impact of quasi-stationary atmospheric rivers on Rossby wave activity in the subtropics

Tuesday, 15 December 2020
Poster
Hung-I Lee, University of Chicago, Department of Geophysical Sciences, Chicago, IL, United States, Noboru Nakamura, University of Chicago, Department of the Geophysical Sciences, Chicago, IL, United States and Jonathan Mitchell, University of California Los Angeles, Department of Atmospheric & Oceanic Sciences; Department of Earth, Planetary & Space Sciences, Los Angeles, CA, United States
Abstract:
Climatology of column water vapor (CWV) at 30режN shows seasonally migrating quasi-stationary atmospheric rivers (QSARs) over the North Pacific and North Atlantic Oceans (Lee et al. 2019). They originate in the Eastern Pacific/Atlantic in winter and propagate to the Western Pacific/Atlantic in summer. East Asian summer monsoon (EASM) onset coincides with the time when the Pacific QSAR makes landfall in East Asia. In this study, we explore possible connections between QSARS and upper tropospheric Rossby wave trains. We find that local wave activity (LWA), a measure of mid-latitude wave meandering, is greatly enhanced on the downstream side of the Pacific/Atlantic QSARs. To explore the primary source of this LWA enhancement, we analyze LWA budgets, which include wave activity fluxes including the Eliassen-Palm (EP) flux and the zonal advection flux, and the residual. Convergence of the EP flux and the zonal advection flux measures the wave forcing due to baroclinic wave packets traveling through an inhomogeneous jet stream, whereas the residual evaluates the source-sink of wave activity due to diabatic heating and mixing. The bimonthly moving average of LWA tendency, a time derivative of LWA (per 6-hour), is positive along the pathway of the westerly migrating QSARs and negative when QSARs retreat easterly. However, near the QSAR pathways, we observe negative wave activity flux convergence, which tend to decrease LWA in the QSARs regions. The mismatch of the patterns between LWA tendency and the flux convergence implies that the enhancement of LWA downstream of QSARs is more likely due to the residual term. Hence, we hypothesize that the LWA enhancement is primarily driven by the diabatic heating from QSARs and is further driven downstream of QSARs by jet streams. We will explore in the ongoing work to test this hypothesis in a simplified moist GCM described in Frierson et al., (2006) with an idealized land-sea configurations.
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