Total rain accumulation and rain‐rate analysis for small tropical Pacific islands: a case study of Suva, Fiji

Kumar, Vickal V.; Deo, Ravinesh C.; Ramachandran, Visagaperuman

doi:10.1002/asl.131

Cited by 22 publications

(14 citation statements)

References 13 publications

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“…Though the SPCZ lies mostly over the South Pacific Ocean, there are many small island states that depend on its rainfall (e.g. Griffiths et al, ; Kumar et al, ). Small displacements in its location have resulted in severe droughts and floods across the region (Cai et al , ).…”

Section: Introductionmentioning

confidence: 99%

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A dynamical framework for the origin of the diagonal South Pacific and South Atlantic Convergence Zones

Wiel

Matthews

Stevens

et al. 2015

Quart J Royal Meteoro Soc

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The South Pacific Convergence Zone (SPCZ) and South Atlantic Convergence Zone (SACZ) are diagonal bands of precipitation that extend from the Equator southeastward into the Southern Hemisphere over the western Pacific and Atlantic Oceans, respectively. With mean precipitation rates over 5 mm day −1 , they are a major component of the tropical and global climate in austral summer. However, their basic formation mechanism is not fully understood. Here, a conceptual framework for the diagonal convergence zones is developed, based on calculations of the vorticity budget from reanalysis and Rossby wave theory.Wave trains propagate eastward along the Southern Hemisphere subtropical jet, with initially quasi-circular vorticity centres. In the zonally sheared environment on the equatorward flank of the jet, these vorticity centres become elongated and develop a northwest-southeast tilt. Ray-tracing diagnostics in a non-divergent, barotropic Rossby wave framework then explain the observed equatorward propagation of these diagonal vorticity structures toward the westerly ducts over the equatorial Pacific and Atlantic. The baroclinic component of these circulations leads to destabilisation and ascent ahead of the cyclonic vorticity anomaly in the wave, triggering deep convection because of the high sea surface temperatures in this region. Latent heat release then forces additional ascent and strong upper-tropospheric divergence, with an associated anticyclonic vorticity tendency. A vorticity budget shows that this cancels out the advective cyclonic vorticity tendency in the wave train over the SPCZ, and dissipates the wave within a day. The mean SPCZ is consequently comprised of the sum of these pulses of diagonal bands of precipitation.Similar mechanisms also operate in the SACZ. However, the vorticity anomalies in the wave trains are stronger, and the precipitation and negative feedback from the divergence and anticyclonic vorticity tendency are weaker, resulting in continued propagation of the wave and a more diffuse diagonal convergence zone.

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Section: Introductionmentioning

confidence: 99%

“…Though the SPCZ lies mostly over the South Pacific Ocean, there are many small island states that depend on its rainfall (e.g. Griffiths et al, 2003;Kumar et al, 2006). Small displacements (a) (b) (c) Figure 1.…”

Section: Introductionmentioning

confidence: 99%

A dynamical framework for the origin of the diagonal South Pacific and South Atlantic Convergence Zones

Wiel

Matthews

Stevens

et al. 2015

Quart J Royal Meteoro Soc

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show abstract

“…Owing to its strong rainfall gradient, a small displacement in the position of the SPCZ causes drastic changes to hydroclimatic conditions and the frequency of extreme weather events-such as droughts, floods and tropical cyclones-experienced by vulnerable island countries in the region [1][2][3][4][5][6][7] . The SPCZ position varies from its climatological mean location with the El Niño/ Southern Oscillation (ENSO), moving a few degrees northward during moderate El Niño events and southward during La Niña events 2,5,6 .…”

mentioning

confidence: 99%

More extreme swings of the South Pacific convergence zone due to greenhouse warming

Cai¹,

Lengaigne²,

Borlace³

et al. 2012

Nature

177

176

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The South Pacific convergence zone (SPCZ) is the Southern Hemisphere's most expansive and persistent rain band, extending from the equatorial western Pacific Ocean southeastward towards French Polynesia. Owing to its strong rainfall gradient, a small displacement in the position of the SPCZ causes drastic changes to hydroclimatic conditions and the frequency of extreme weather events--such as droughts, floods and tropical cyclones--experienced by vulnerable island countries in the region. The SPCZ position varies from its climatological mean location with the El Niño/Southern Oscillation (ENSO), moving a few degrees northward during moderate El Niño events and southward during La Niña events. During strong El Niño events, however, the SPCZ undergoes an extreme swing--by up to ten degrees of latitude toward the Equator--and collapses to a more zonally oriented structure with commensurately severe weather impacts. Understanding changes in the characteristics of the SPCZ in a changing climate is therefore of broad scientific and socioeconomic interest. Here we present climate modelling evidence for a near doubling in the occurrences of zonal SPCZ events between the periods 1891-1990 and 1991-2090 in response to greenhouse warming, even in the absence of a consensus on how ENSO will change. We estimate the increase in zonal SPCZ events from an aggregation of the climate models in the Coupled Model Intercomparison Project phases 3 and 5 (CMIP3 and CMIP5) multi-model database that are able to simulate such events. The change is caused by a projected enhanced equatorial warming in the Pacific and may lead to more frequent occurrences of extreme events across the Pacific island nations most affected by zonal SPCZ events.

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“…Marked differences were observed in the lightning activity between the two seasons, carried out using the Lightning Imaging Sensor satellite data and ground based WWLLN measurements (Ramachandran et al, 2005). Likewise, long-term rainfall studies at Suva also revealed distinct seasonal dependence (Kumar et al, 2006). In Fig.…”

Section: Comparison With Global Trendsmentioning

confidence: 82%

Surface fair-weather potential gradient measurements from a small tropical island station Suva, Fiji

et al. 2009

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Systematic analysis of the surface fair-weather potential gradient (PG) measured for 13 months (July 2005-July 2006) at 10 s resolution over a small tropical island station Suva (18.08• S, 178.45• E), Fiji is presented. Based on the solar radiation (>800 W m −2 ) and surface wind speed (<4.5 m s −1 ) conditions, 63 fair-weather days were selected. After sorting the data into a range of 0-1000 V m −1 , the average PG was ∼139 V m −1 . The measured fair-weather PG had a semi-diurnal structure, with a more pronounced peak at 0730 LT (1930 UT) and a reduced peak at 2200 LT (1000 UT). The time of occurrence of the morning peak and the noontime minima agreed well with the Carnegie curve. However, the variation about the global mean in the measured PG was 150% whereas for the Carnegie curve it was only 35%. The effects of the local meteorological parameters on the PG measurements were found to be small. On average, the PG during the dry season (May-October) was always greater than in the wet season (November-April). In contrast, analysis of regional (0-60• S and 100• E-160• W) lightning activity on fair-weather days showed a peak at ∼2000 LT and higher lightning activity during the wet season. These results indicate that the regional thunderstorm activity has no direct connection with the local fair-weather PG at the site.

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Total rain accumulation and rain‐rate analysis for small tropical Pacific islands: a case study of Suva, Fiji

Cited by 22 publications

References 13 publications

A dynamical framework for the origin of the diagonal South Pacific and South Atlantic Convergence Zones

A dynamical framework for the origin of the diagonal South Pacific and South Atlantic Convergence Zones

More extreme swings of the South Pacific convergence zone due to greenhouse warming

Surface fair-weather potential gradient measurements from a small tropical island station Suva, Fiji

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