[1] Interannual variability, seasonal evolution, and intraseasonal variability of the South Pacific Convergence Zone (SPCZ) are quantified using a new data set of 3-hourly SPCZ labels, available from 1980 to 2012 Nov-Apr. The SPCZ label is a binary field indicating presence (1) or absence (0) of the SPCZ at each grid point (½°longitude by ½°latitude) as a function of time and is the output of a Bayesian spatiotemporal statistical model that takes in instantaneous data from geostationary satellites. The statistical model is designed to emulate the way human observers identify the SPCZ. Results show two distinct parts to the SPCZ: the western tropical part and the eastern subtropical part. At times, the two parts do not connect. When they do connect, they are oriented quite differently, such that the subtropical part has a steeper meridional slope. The SPCZ is present 50-70% of the time in the tropics from Jan to Mar and is usually anchored to the warm sea surface temperature (SST) distribution of the equatorial west Pacific. The subtropical part does not have the same sensitivity to the underlying SST distribution and is present more often in Nov-Dec and Apr than in Jan-Mar when the SST is highest. Interannual variability in SPCZ location is strongly associated with El Niño-Southern Oscillation (ENSO); however, no change in overall SPCZ area is detected in association with ENSO. On the intraseasonal time scale, composite analysis shows the distinct spatial patterns in SPCZ presence associated with each phase of the Madden Julian Oscillation.

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

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A data set of three-hourly South Pacific Convergence Zone (SPCZ) location and extent, from which IR temperature within the SPCZ may be obtained, for 1980-2012, November-April is used to examine the diurnal cycle of the SPCZ. Maximum SPCZ area occurs at 15:00-18:00 local standard time (LST). Two minima in mean IR temperature are evident, one at 13:00-16:00 LST, nearly coinciding with the maximum in area, and the second in the early morning hours at 05:00-07:00 LST, when area is at a minimum. The morning minimum in mean IR temperature is associated with a peak in deep convection while the afternoon minimum is associated with a peak in midlevel clouds. On average, the morning minimum in IR temperature dominates in the tropical regions of the SPCZ, while the afternoon IR temperature minimum dominates in the subtropical regions of the SPCZ. The relative strength of the two IR temperature minima is affected by the seasonal cycle, intraseasonal variability associated with active Madden Julian Oscillation events, and interannual variability due to the El Niño Southern Oscillation. The morning IR temperature minimum becomes more dominant when the SPCZ is more frequently present or when the SPCZ is shifted toward the equator. In terms of cloud height, midlevel clouds dominate at all times in all regions of the SPCZ and peak in abundance between 15:00-18:00 LST. Low-level clouds peak near midnight and then transition to high-level clouds, which peak between 03