Changes in atmospheric circulation patterns associated with high and low rainfallregimes in the Hawaiian Islands region on multiple time scales

Changes in atmospheric circulation patterns associated with high and low rainfall regimes in the Hawaiian Islands region on multiple time scales" (2012). a b s t r a c t a r t i c l e i n f o Keywords: Hawai'i rainfall Seasonal to multi-decadal variability Characteristic patterns of anomalous large‐ scale circulation Climatic changes We examine a suite of climate variables in the North Pacific associated with different temporal scales of dry and wet episodes in the Hawaiian Islands. The goal is to ascertain whether varying the length in the occurrence of such events from seasonal to multi-decadal results from different ocean–atmosphere circulation patterns over the North Pacific region. We find that as the dryness period lengthens, the spatial scale of the anomalies widens, but the characteristics of the anomalous circulation fields exhibit elements evident at each time scale. At the longest (multi-decadal) time scales during the wet season (November–April), the major anomalous circulation features associated with above (below) average rainfall in Hawai'i are a strengthening (weakening) of the North Pacific mid-latitude westerlies associated with a strengthened (weakened) Aleutian Low system, a slight weakening (strengthening) of the northeast trade winds, with anomalous northerly (southerly) component to the south of the Islands, together with diminished (enhanced) precipitation across most of the tropical North Pacific. During the summer dry season (May–October) a characteristic pattern that is evident at different time scales during drier than normal periods is a strengthening of the trade winds to the south of the Islands, with sinking motion extending from the latitude of Hawai'i eastward to Central America. Conversely, wet summers are associated with generally weaker trades to the south with a tendency for anomalous southwesterly component. We also consider possible changes in the relationship of Hawaiian rainfall to changes in the Pacific-Decadal Oscillation (PDO) but conclude that the record is too short to establish the significance of any changes in an overall negative correlation. Although the Hawaiian Islands contain some of the rainiest sites on Earth, periods of sustained dryness do affect the Islands periodically (Giambelluca et al., 1991). Some previous studies that have examined rainfall variability in Hawai'i include those by Lyons (1982) and Chu (1989) for seasonal means, and those by Chu and Chen (2005), Timm and Diaz (2009), Chu et al. (2010), and Elison Timm et al. (2011) for interannual to decadal and longer timescales. Secular trends are also evident in …