Daily States of the March–April East Pacific ITCZ in Three Decades of High-Resolution Satellite Data

Haffke, C. M.; Magnúsdóttir, Guðrún; Henke, Daniel; Smyth, Padhraic; Peings, Yannick

doi:10.1175/jcli-d-15-0224.1

Cited by 27 publications

(37 citation statements)

References 34 publications

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“…Since the circulation is not primarily meridional near the rising branch of the Walker circulation, we exclude the western Pacific sector from the analysis. In addition, frequent bifurcations from single-to double-ITCZ states occur during boreal spring in the central Pacific (Haffke et al 2016). Conditional averaging of daily precipitation would therefore be required for a quantitative analysis there.…”

Section: B Sector-mean Efementioning

confidence: 99%

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Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part II: Zonally Varying Shifts of the ITCZ

2016

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The ITCZ lies at the ascending branch of the tropical meridional overturning circulation, where nearsurface meridional mass fluxes vanish. Near the ITCZ, column-integrated energy fluxes vanish, forming an atmospheric energy flux equator (EFE). This paper extends existing approximations relating the ITCZ position and EFE to the atmospheric energy budget by allowing for zonal variations. The resulting relations are tested using reanalysis data for 1979-2014. The zonally varying EFE is found as the latitude where the meridional component of the divergent atmospheric energy transport (AET) vanishes. A Taylor expansion of the AET around the equator relates the ITCZ position to derivatives of the AET. To a first order, the ITCZ position is proportional to the divergent AET across the equator; it is inversely proportional to the local atmospheric net energy input (NEI) that consists of the net energy fluxes at the surface, at the top of the atmosphere, and zonally across longitudes. The first-order approximation captures the seasonal migrations of the ITCZ in the African, Asian, and Atlantic sectors. In the eastern Pacific, a third-order approximation captures the bifurcation from single-to double-ITCZ states that occurs during boreal spring. In contrast to linear EFE theory, during boreal winter in the eastern Pacific, northward cross-equatorial AET goes along with an ITCZ north of the equator. EFE and ITCZ variations driven by ENSO are characterized by an equatorward (poleward) shift in the Pacific during El Niño (La Niña) episodes, which are associated with variations in equatorial ocean energy uptake.

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Section: B Sector-mean Efementioning

confidence: 99%

“…9c) NEI. We examine the annual-mean response in order to reduce the sensitivity of the analysis to ITCZ bifurcations, which are most frequent during boreal spring (e.g., Haffke et al 2016). Like the ITCZ (Fig.…”

Section: Efe Response To Ensomentioning

confidence: 99%

Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part II: Zonally Varying Shifts of the ITCZ

2016

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“…During the austral summer in the eastern Pacific the ITCZ tends to remain to the north of the equator although with much decreased activity compared to boreal summer. Outside of boreal summer there is considerably more variability in the location of the ITCZ with respect to the equator (Henke et al 2012;Haffke et al 2016). On daily time scales the ITCZ may exist in five different states with respect to the equator.…”

Section: Introductionmentioning

confidence: 99%

“…These were the original four states of the east Pacific ITCZ that were identified by Henke et al (2012) in five years of daily geostationary satellite data . The fifth state was only identified when Haffke et al (2016) extended the study and analyzed data from 1980 to 2012, years that include strong east Pacific El Niño years such as 1997/98 and 1982/83 and were dominated by a strong east Pacific ITCZ located over the equator (eITCZ, for equatorial ITCZ). The fact that the east Pacific El Niño (EP El Niño; e.g., Kao and Yu 2009) has an ITCZ state all to itself serves as a reminder of the dominance of interannual variability associated with El Niño-Southern Oscillation (ENSO) on elongated convection zones over the tropical Pacific.…”

Section: Introductionmentioning

confidence: 99%

“…In some models this bias is present throughout the annual cycle whereas observations have shown that the dITCZ mostly occurs in March-April or in boreal spring. Figure 1 is reproduced from Haffke et al (2016) and shows the distribution of daily states of the ITCZ through the annual cycle (January-December, x axis) and from 1980 (top of y axis) to 2012. Certain characteristics are readily apparent.…”

Section: Introductionmentioning

confidence: 99%

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Interannual Signature in Daily ITCZ States in the East Pacific in Boreal Spring

Yang

Magnúsdóttir

2016

Journal of Climate

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The intertropical convergence zone (ITCZ) in the east Pacific is located north of the equator during most of the year. In daily data it is most variable in March-April when it may be located north of the equator (nITCZ), on both sides of the equator (dITCZ), or south of the equator (sITCZ), or it may be absent (when convection does not take on a zonally elongated form). Additionally, in strong El Niño years it is located on the equator during the boreal winter half-year. Here the focus is on conditions when the ITCZ has a presence south of the equator (dITCZ, sITCZ) and composites of various fields are compared to ''normal conditions'' [i.e., when the ITCZ is north of the equator (nITCZ)]. Composites of sea surface temperature (SST), precipitation, outgoing longwave radiation, and the upper-level circulation show very similar patterns for dITCZ and sITCZ days, where the latter cases have almost double the amplitude of the former. The sITCZ state is viewed as an extreme case of the dITCZ state. Both are found to be related to the central Pacific (CP) La Niña with anomalous positive SST and atmospheric heating over the western tropical Pacific and anomalous negative SST and cooling over the central tropical Pacific. Ocean-atmosphere interaction plays an important role in developing the dITCZ and sITCZ anomalies. These daily composite patterns can be reproduced by the regression of monthly fields on the cold CP El Niño-Southern Oscillation mode, suggesting that the interannual rather than day-to-day variability dominates in contributing to the patterns of the composites.

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Explaining the Year‐to‐Year Variability of the Eastern Pacific Intertropical Convergence Zone in the Boreal Spring

Haiyang

Zhang

2018

JGR Atmospheres

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The year‐to‐year variability of the Intertropical Convergence Zone (ITCZ) in the eastern tropical Pacific is a significant phenomenon of the tropical climate system. Asymmetric interannual variation of precipitation on two sides of the Equator is often observed there in the boreal spring. We introduce a simple normalized asymmetric index and a double ITCZ index as well as a hierarchical clustering method to describe the ITCZ variation based on the tropical boreal spring precipitation from 1979 to 2017. We show that the indices and the clustering method give consistent categorization of asymmetric ITCZ variation. We find that the asymmetry of precipitation can be explained by the remote impact of the interannual variability of the central Pacific sea surface temperature (SST) on the horizontal gradient of surface pressure and surface wind convergence, especially the Modoki mode. The central Pacific SST also remotely modulates free‐tropospheric temperature and vertical stability in the eastern equatorial Pacific, but this remote impact is secondary to the wind convergence. Interannual variability of local SST south of the Equator plays little role in the precipitation variability, which is supported by numerical experiments with a regional atmospheric model. Results imply that surface wind convergence should be considered in convection schemes to improve the simulation of precipitation in the eastern tropical Pacific in climate models.

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Daily States of the March–April East Pacific ITCZ in Three Decades of High-Resolution Satellite Data

Cited by 27 publications

References 34 publications

Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part II: Zonally Varying Shifts of the ITCZ

Seasonal and Interannual Variations of the Energy Flux Equator and ITCZ. Part II: Zonally Varying Shifts of the ITCZ

Interannual Signature in Daily ITCZ States in the East Pacific in Boreal Spring

Explaining the Year‐to‐Year Variability of the Eastern Pacific Intertropical Convergence Zone in the Boreal Spring

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