A comparison of the effects of El Ni?o and El Ni?o Modoki on subdaily extreme precipitation occurrences across the contiguous United States

摘要

Intense precipitation over a short duration is a major cause of flash floods. Using hourly rainfall data from the North America Land Data Assimilation System Phase 2 from 1979 to 2013, we compared the differences in the response of the subdaily extreme precipitation occurrences across the contiguous U.S. to strong anomalous warming over the eastern equatorial Pacific known as El Ni?o and over the central equatorial Pacific known as El Ni?o Modoki. For both types of anomalous equatorial Pacific warming, the teleconnection is much stronger in the cold season (November through April) than warm season (May through October). During the warm season, while both types correspond to an increase in subdaily extreme precipitation in areas of Texas and a decrease in some areas of the northern Plains, El Ni?o is associated with a significant increase in the northern Rockies and El Ni?o Modoki is associated with a decrease in the Intermountain West. During the cold season, the overall patterns are similar between the two types, with positive anomalies over much of the southern and negative anomalies over the northern U.S. However, large regional differences exist, with El Ni?o exerting a much stronger influence on subdaily extreme precipitation in the Atlantic and Gulf states as well as California, while the influence of El Ni?o Modoki is slightly broader over the Midwest. These differences can be largely explained by the vertical velocity, moisture convergence, and jet stream patterns induced by El Ni?o and El Ni?o Modoki episodes.