Ma, C. G., Chang, E. K., Wong, S., Zhang, R., Zhang, M., & Del Genio, A. (2020). Impacts of storm track variations on winter time extreme precipitation and moisture budgets over the Ohio Valley and Northwestern US. Journal of Climate, (2020).
Differences in the dynamics governing cyclone related wintertime extreme precipitation events over the Ohio Valley and the Pacific Northwest (Ma et al., 2020)
Link to paper
Our previous study (Ma and Chang, 2017) has shown that variations in extratropical cyclone activity significantly affect the frequency of extreme precipitation events over the Ohio Valley and northwestern United States. In this study, we examine the similarities and differences between the dynamics governing these events in these two regions. In the Ohio Valley, extreme precipitation events are associated with midlatitude synoptic-scale convergence northeast of cyclones and a southwestward oriented ridge near the Atlantic coast that drives strong water vapor transport from the Gulf of Mexico into the Ohio Valley. Our results suggest that both the cyclone and the extended ridge are important in driving the enhanced moisture flux towards the Ohio Valley (Fig. 1).
Anomalies of SLP and moisture flux averaged for the composite that are (a),(b) extreme precipitation days for the box and have at least one cyclone located near the southwest corner of the box on that day (99 days); (c),(d) extreme precipitation days for the box but have no cyclone located near the southwest corner of the box on that day (46 days); and (e),(f) nonextreme precipitation days but have at least one cyclone located near the southwest corner of the box that day with a daily maximum intensity at least 17 hPa (26 days). Adopted from Ma et al. (2020).
In the northwestern United States, extreme precipitation events are associated with a cyclonic and anticyclonic circulation pair aligned northwest to southeast, which together drive a long and strong moisture transport corridor from the lower latitude of the central Pacific Ocean toward the northwestern United States. Moisture budget analysis shows that moisture convergence due to dynamical convergence dominates in the Ohio Valley, whereas moisture advection dominates over the Pacific Northwest. Differences between the cases in the same region are examined by an empirical orthogonal function (EOF) analysis conducted on the vertically integrated moisture flux. Different EOFs highlight shifts in spatial location, orientation, and intensity of the moisture flux but demonstrate consistent roles of dynamics in the two regions. Composites based on these EOFs highlight the range of likely synoptic scenarios that can give rise to precipitation extremes over these two regions. These results are published in the Journal of Climate, 33, 5371-5391)
