Abstract
Zonally elongated areas of cloudiness that make up the east Pacific Intertropical 25 Convergence Zone (ITCZ) can take on several configurations in instantaneous 26 observations. A novel statistical model is used to automatically assess the daily state of 27 the east Pacific ITCZ using infrared satellite images from 1980-2012. Four ITCZ states 28 are defined based on ITCZ location relative to the equator: north (nITCZ) and south 29 (sITCZ) of the equator, simultaneously north and south of the equator (dITCZ, for 30 double), and over the equator (eITCZ). A fifth ITCZ state is used to classify days when 31 no zonally elongated area of cloudiness is present (aITCZ, for absent). The ITCZ states 32 can occur throughout the year (except for the eITCZ, which is not present during June–33 October), with the nITCZ state dominating in terms of frequency of occurrence. 34 Interannual variability of the state distribution is large.
35 The most striking variability in ITCZ states is observed in spring. During March-36 April, the dITCZ state occurs on average 34% of the time, second only to the nITCZ state 37 (39%). Composites of observed infrared temperature and precipitation by ITCZ state 38 reveal distinct spatial configurations of cloudiness and rainfall. Strong sea surface 39 temperature anomalies are associated only with eITCZ and sITCZ and they correspond to 40 El Nino and La Nina, respectively. However, all five ITCZ states are associated with 41 distinct atmospheric circulation patterns. A connection is found between the ITCZ and 42 the South Pacific Convergence Zone (SPCZ), such that activity in the SPCZ is enhanced 43 when the ITCZ is absent in the east Pacific.
Haffke, Colene