scholarly journals Application of Clustering Algorithms to TRMM Precipitation over the Tropical and South Pacific Ocean

2020 ◽  
Vol 33 (13) ◽  
pp. 5767-5785 ◽  
Author(s):  
Maxwell Pike ◽  
Benjamin R. Lintner
Keyword(s):  
Southern Oscillation ◽  
Rainfall Variability ◽  
Deep Convection ◽  
South Pacific ◽  
Empirical Orthogonal Functions ◽  
South Pacific Convergence Zone ◽  
Specific Humidity ◽  
The South ◽  
Cluster Assignment ◽  
Trmm Precipitation

AbstractUnderstanding multiscale rainfall variability in the South Pacific convergence zone (SPCZ), a southeastward-oriented band of precipitating deep convection in the South Pacific, is critical for both the human and natural systems dependent on its rainfall, and for interpreting similar off-equatorial diagonal convection zones around the globe. A k-means clustering method is applied to daily austral summer (December–February) Tropical Rainfall Measuring Mission (TRMM) satellite rainfall to extract representative spatial patterns of rainfall over the SPCZ region for the period 1998–2013. For a k = 4 clustering, pairs of clusters differ predominantly via spatial translation of the SPCZ diagonal, reflecting either warm or cool phases of El Niño–Southern Oscillation (ENSO). Within each of these ENSO phase pairs, one cluster exhibits intense precipitation along the SPCZ while the other features weakened rainfall. Cluster temporal behavior is analyzed to investigate higher-frequency forcings (e.g., the Madden–Julian oscillation and synoptic-scale disturbances) that trigger deep convection where SSTs are sufficiently warm. Pressure-level winds and specific humidity from the Climate Forecast System Reanalysis are composited with respect to daily cluster assignment to investigate differences between active and quiescent SPCZ conditions to reveal the conditions supporting enhanced or suppressed SPCZ precipitation, such as low-level poleward moisture transport from the equator. Empirical orthogonal functions (EOFs) of TRMM precipitation are computed to relate the “modal view” of SPCZ variability associated with the EOFs to the “state view” associated with the clusters. Finally, the cluster number is increased to illustrate the change in TRMM rainfall patterns as additional degrees of freedom are permitted.

scholarly journals Scope for predicting seasonal variation of the SPCZ with ACCESS-S1

2021 ◽  
Author(s):  
Thomas A. Beischer ◽  
Paul Gregory ◽  
Kavina Dayal ◽  
Josephine R. Brown ◽  
Andrew N. Charles ◽  
...  
Keyword(s):  
Pacific Islands ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
South Pacific ◽  
Seasonal Rainfall ◽  
South Pacific Convergence Zone ◽  
The South ◽  
Local Conditions ◽  
Local Climate ◽  
Seasonal Rainfall Forecasts

AbstractRegional seasonal forecasting requires accurate simulation of the variability of local climate drivers. The South Pacific Convergence Zone (SPCZ) is a large region of low-level convergence, clouds and precipitation in the South Pacific, whose effects extend as far as northeast Australia (NEA). The location of the SPCZ is modulated by the El Niño-Southern Oscillation (ENSO) which causes rainfall variability in the region. Correctly simulating the ENSO-SPCZ teleconnection and its interplay with local conditions is essential for improving seasonal rainfall forecasts. Here we analyse the ability of the ACCESS-S1 seasonal forecast system to predict the SPCZ’s relationship with ENSO including its latitudinal shifts, zonal slope and rainfall magnitude between 1990 and 2012 for the December–January–February (DJF) season. We found improvements in ACCESS-S1’s SPCZ prediction capability compared to its predecessor (POAMA), although prediction of the slope is still limited. The inability of ACCESS-S1 to replicate seasons with a strong anti-zonal SPCZ slope is attributed to its atmospheric model. This has implications for accurate seasonal rainfall forecasts for NEA and South Pacific Islands. Future challenges in seasonal prediction facing regional communities and developers of coupled ocean–atmosphere forecast models are discussed.

The role of air-sea coupling on the simulation of intraseasonal rainfall variability over the South Pacific in ECHAM5-SIT

2021 ◽  
Author(s):  
Sunil Kumar Pariyar ◽  
Noel Keenlyside ◽  
Wan-Ling Tseng
Keyword(s):  
General Circulation ◽  
Rainfall Variability ◽  
Intraseasonal Variability ◽  
Phase Relationship ◽  
Coupled Model ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
The South ◽  
The Impact

<p><span>We investigate the impact of air-sea coupling on the simulation of the intraseasonal variability of rainfall over the South Pacific using the ECHAM5 atmospheric general circulation model coupled with Snow-Ice-Thermocline (SIT) ocean model. We compare the fully coupled simulation with two uncoupled simulations forced with sea surface temperature (SST) climatology and daily SST from the coupled model. The intraseasonal rainfall variability over the South Pacific Convergence Zone (SPCZ) is reduced by 17% in the uncoupled model forced with SST climatology and increased by 8% in the uncoupled simulation forced with daily SST. The coupled model best simulates the key characteristics of the two intraseasonal rainfall modes of variability in the South Pacific, as identified by an Empirical Orthogonal Function (EOF) analysis. The spatial structure of the two EOF modes in all three simulations is very similar, suggesting these modes are independent of air-sea coupling and primarily generated by the dynamics of the atmosphere. The southeastward propagation of rainfall anomalies associated with two leading rainfall modes in the South Pacific depends upon the eastward propagating </span><span>Madden-Julian Oscillation (</span><span>MJO</span><span>)</span><span> signals over the Indian Ocean and western Pacific. Air-sea interaction seems crucial for such propagation as both eastward and southeastward propagations substantially reduced in the uncoupled model forced with SST climatology. Prescribing daily SST from the coupled model improves the simulation of both eastward and southeastward propagations in the uncoupled model forced with daily SST, showing the role of SST variability on the propagation of the intraseasonal variability, but the periodicity differs from the coupled model. The change in the periodicity is attributed to a weaker SST-rainfall relationship that shifts from SST leading rainfall to a nearly in-phase relationship in the uncoupled model forced with daily SST.</span></p>

Understanding the role of water vapor and temperature in easterly wave-related convection

2020 ◽  
Author(s):  
Rosa Vargas Martes ◽  
Angel Adames Corraliza
Keyword(s):  
Water Vapor ◽  
Rainfall Variability ◽  
Large Fraction ◽  
Deep Convection ◽  
Linear Regression Analysis ◽  
Empirical Orthogonal Functions ◽  
Specific Humidity ◽  
Coupling Mechanism ◽  
Orthogonal Functions ◽  
The Relationship

<p>Easterly Waves (EW) in the Pacific Ocean (PEW) and over Africa (AEW) account for a large fraction of rainfall variability in their respective regions. Although multiple studies have been conducted to better understand EWs, many questions remain regarding their structure, development, and coupling to deep convection. Recent studies have highlighted the relationship between water vapor and precipitation in tropical motion systems. However, EW have not been studied within this context. On the basis of Empirical Orthogonal Functions (EOFs) and a novel plume-buoyancy framework, the thermodynamic processes associated with EW-related convection are elucidated. A linear regression analysis reveals the relationship between temperature, moisture, and precipitation in EW. Temperature anomalies are found to be highly correlated in space and time with anomalies in specific humidity. However, this coupling between temperature and moisture is more robust in AEWs than PEWs. In PEWs moisture accounts for a larger fraction of precipitation variability. Results suggest that the convective coupling mechanism in AEW may differ from the coupling mechanism of PEWs.</p>

scholarly journals The Representation of the South Pacific Convergence Zone in the Twentieth Century Reanalysis

2019 ◽  
Vol 147 (3) ◽  
pp. 841-851 ◽  
Author(s):  
Thomas Harvey ◽  
James A. Renwick ◽  
Andrew M. Lorrey ◽  
Arona Ngari
Keyword(s):  
Twentieth Century ◽  
Southern Oscillation ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Past Century ◽  
Convergence Zone ◽  
The South ◽  
Southwest Pacific ◽  
Surface Observations ◽  
Twentieth Century Reanalysis

Abstract The South Pacific convergence zone (SPCZ) is the largest rainfall feature in the Southern Hemisphere, and is a critical component of the climate for South Pacific island nations and territories. The small size and isolated nature of these islands leaves them vulnerable to short- and long-term changes in the position of the SPCZ. Its position and strength is strongly modulated by El Niño–Southern Oscillation (ENSO), leading to large interannual variability in rainfall across the southwest Pacific including seasonal droughts and pluvials. Currently much of the analysis about SPCZ activity has been restricted to the satellite observation period starting in 1979. Here, the representation of the SPCZ in the Twentieth Century Reanalysis (20CR), which is a three-dimensional atmospheric reconstruction based only on surface observations, is discussed for the period since 1908. The performance of two versions of the 20CR (version 2 and version 2c) in the satellite era is compared with other reanalyses and climate observation products. The 20CR performs well in the satellite era. Extra surface observations spanning the SPCZ region from the longitude of the Cook Islands has improved the representation of the SPCZ during 1908–57 between 20CRv2 and 20CRv2c. The well-established relationship with ENSO is observed in both the representation of mean SPCZ position and intensity, and this relationship remains consistent through the entire 1908–2011 period. This suggests that the ENSO–SPCZ relationship has remained similar over the course of the past century, and gives further evidence that 20CRv2c performs well back to 1908 over the southwest Pacific region.

scholarly journals Mesoscale Simulation of Tropical Cyclones in the South Pacific: Climatology and Interannual Variability

2011 ◽  
Vol 24 (1) ◽  
pp. 3-25 ◽  
Author(s):  
Nicolas C. Jourdain ◽  
Patrick Marchesiello ◽  
Christophe E. Menkes ◽  
Jérome Lefèvre ◽  
Emmanuel M. Vincent ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Southern Oscillation ◽  
Regional Scale ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Dimensional Structure ◽  
The South ◽  
Wide Range

Abstract The Weather Research and Forecast model at ⅓° resolution is used to simulate the statistics of tropical cyclone (TC) activity in the present climate of the South Pacific. In addition to the large-scale conditions, the model is shown to reproduce a wide range of mesoscale convective systems. Tropical cyclones grow from the most intense of these systems formed along the South Pacific convergence zone (SPCZ) and sometimes develop into hurricanes. The three-dimensional structure of simulated tropical cyclones is in excellent agreement with dropsondes and satellite observations. The mean seasonal and spatial distributions of TC genesis and occurrence are also in good agreement with the Joint Typhoon Warning Center (JTWC) data. It is noted, however, that the spatial pattern of TC activity is shifted to the northeast because of a similar bias in the environmental forcing. Over the whole genesis area, 8.2 ± 3.5 cyclones are produced seasonally in the model, compared with 6.6 ± 3.0 in the JTWC data. Part of the interannual variability is associated with El Niño–Southern Oscillation (ENSO). ENSO-driven displacement of the SPCZ position produces a dipole pattern of correlation and results in a weaker correlation when the opposing correlations of the dipole are amalgamated over the entire South Pacific region. As a result, environmentally forced variability at the regional scale is relatively weak, that is, of comparable order to stochastic variability (±1.7 cyclones yr−1), which is estimated from a 10-yr climatological simulation. Stochastic variability appears essentially related to mesoscale interactions, which also affect TC tracks and the resulting occurrence.

scholarly journals The South Pacific Convergence Zone as Depicted in Reanalysis and Satellite Products

2021 ◽  
Author(s):  
◽  
Harvey Thomas Luke
Keyword(s):  
Twentieth Century ◽  
Southern Oscillation ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Past Century ◽  
Enso Cycle ◽  
Convergence Zone ◽  
The South ◽  
Southwest Pacific ◽  
Extended Analysis

<p>The South Pacific Convergence Zone (SPCZ) is the largest rainfall feature in the Southern Hemisphere, and is a critical component of the climate of Southwest Pacific Island nations. The small size and isolated nature of these islands leaves them vulnerable to short and long term changes in the position of the SPCZ. Its location and strength is strongly modulated by the El Niño-Southern Oscillation (ENSO) cycle and the Inter-decadal Pacific Oscillation (IPO), leading to large inter-annual and decadal variability in rainfall across the Southwest Pacific. Much of the analysis on the SPCZ has been restricted to the modern period, more specifically the “satellite era”, starting in 1979. Here, the representation of the SPCZ in the Twentieth Century Reanalysis (20CR) product, which reconstructs the three-dimensional state of the atmosphere based only on surface observations is discussed. The performance of two versions of the 20CR (versions 2 and 2c) in the satellite era is tested via inter-comparison with other reanalysis and observational satellite products, before using 20CR version 2c (20CRv2c) to perform extended analysis back to the early twentieth century. This study demonstrates that 20CR performs well in the satellite era, and is considered suitable for extended analysis. It is established that extra data added in the SPCZ region between 20CR versions 2 and 2c has improved the representation of the SPCZ during 1908-1958. Well-established relationships between ENSO and the IPO with the SPCZ are shown to be present through the entire 1908-2011 period, although it is suggested that the physical link between the IPO and the SPCZ has changed between the first and second half of the twentieth century. Finally, evidence of a southward trend of the SPCZ over the past century is presented, potentially due to an expansion of the tropics as a result of climate change.</p>

A 1300-year reconstruction of the South Pacific Convergence Zone using a Pacific-wide tree-ring network

2020 ◽  
Author(s):  
Philippa Higgins ◽  
Jonathan Palmer ◽  
Christian Turney ◽  
Martin Andersen ◽  
Edward Cook
Keyword(s):  
Tree Ring ◽  
General Circulation ◽  
Southern Oscillation ◽  
South Pacific ◽  
Ice Age ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Pacific Island ◽  
The South ◽  
Island Communities

&lt;p&gt;The South Pacific Convergence Zone (SPCZ) is the largest driver of precipitation variability over South Pacific island communities during the austral warm season influencing the severity and duration of drought and the frequency of tropical cyclones. The SPCZ is known to exhibit variability on a range of timescales, from intra-seasonal to multidecadal variations, modulated by the Interdecadal Pacific Oscillation (IPO). Despite its climatic and societal importance, determining the causes of low frequency variability in the SPCZ has been hampered by the short instrumental data record, with most comprehensive analyses since the satellite era. Here we report the first paleoclimate reconstruction of the SPCZ, allowing climate variability in the South Pacific region to be explored back to 700 CE. Our 1300-year reconstruction of the SPCZI (South Pacific Convergence Zone Index; the difference between mean sea level pressure between Apia, Samoa and Suva, Fiji) is based on a trans-Pacific network of precisely dated tree-ring proxies. Capturing SPCZ teleconnections from both sides of the Pacific has produced a robust, unbiased reconstruction with excellent reconstruction skill over the entire period. El Ni&amp;#241;o-Southern Oscillation periodicities (&amp;#8764;3-7 years) are pervasive throughout the SPCZI reconstruction. Multidecadal periodicities wax and wane, apparently coinciding with the timing of the Medieval Climate Anomaly (c. 1000-1200 CE) and Little Ice Age (1300-1700 CE). We discuss some of the drivers of SPCZI variability including global dimming events. Our reconstruction helps improve our understanding of past hydroclimatic behaviour in the southwest Pacific and can be used to validate general circulation model projections for Pacific Island communities in the twenty-first century.&lt;/p&gt;

scholarly journals The South Pacific Convergence Zone as Depicted in Reanalysis and Satellite Products

2021 ◽  
Author(s):  
◽  
Harvey Thomas Luke
Keyword(s):  
Twentieth Century ◽  
Southern Oscillation ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Past Century ◽  
Enso Cycle ◽  
Convergence Zone ◽  
The South ◽  
Southwest Pacific ◽  
Extended Analysis

<p>The South Pacific Convergence Zone (SPCZ) is the largest rainfall feature in the Southern Hemisphere, and is a critical component of the climate of Southwest Pacific Island nations. The small size and isolated nature of these islands leaves them vulnerable to short and long term changes in the position of the SPCZ. Its location and strength is strongly modulated by the El Niño-Southern Oscillation (ENSO) cycle and the Inter-decadal Pacific Oscillation (IPO), leading to large inter-annual and decadal variability in rainfall across the Southwest Pacific. Much of the analysis on the SPCZ has been restricted to the modern period, more specifically the “satellite era”, starting in 1979. Here, the representation of the SPCZ in the Twentieth Century Reanalysis (20CR) product, which reconstructs the three-dimensional state of the atmosphere based only on surface observations is discussed. The performance of two versions of the 20CR (versions 2 and 2c) in the satellite era is tested via inter-comparison with other reanalysis and observational satellite products, before using 20CR version 2c (20CRv2c) to perform extended analysis back to the early twentieth century. This study demonstrates that 20CR performs well in the satellite era, and is considered suitable for extended analysis. It is established that extra data added in the SPCZ region between 20CR versions 2 and 2c has improved the representation of the SPCZ during 1908-1958. Well-established relationships between ENSO and the IPO with the SPCZ are shown to be present through the entire 1908-2011 period, although it is suggested that the physical link between the IPO and the SPCZ has changed between the first and second half of the twentieth century. Finally, evidence of a southward trend of the SPCZ over the past century is presented, potentially due to an expansion of the tropics as a result of climate change.</p>

scholarly journals Mechanisms of Mid-Holocene Precipitation Change in the South Pacific Convergence Zone

2013 ◽  
Vol 26 (18) ◽  
pp. 6937-6953 ◽  
Author(s):  
Damianos F. Mantsis ◽  
Benjamin R. Lintner ◽  
Anthony J. Broccoli ◽  
Myriam Khodri
Keyword(s):  
Deep Convection ◽  
Austral Summer ◽  
Circulation Model ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Quasi Equilibrium ◽  
The South ◽  
Australian Monsoon ◽  
Stretching Deformation

Abstract The variability of the South Pacific convergence zone (SPCZ) during the mid-Holocene is investigated using models archived in the Paleoclimate Modelling Intercomparison Project Phase II (PMIP2) database. Relative to preindustrial conditions, mid-Holocene top-of-atmosphere insolation was relatively lower during austral summer [December–February (DJF)], which is the season when the SPCZ is at its peak intensity. In response to this perturbation, the PMIP2 models simulate a displacement of the SPCZ to the southwest. This SPCZ shift is associated with a sea surface temperature (SST) dipole, with increased rainfall collocated with warm SST anomalies. Decomposing the DJF precipitation changes in terms of a diagnostic moisture budget indicates that the SPCZ shift is balanced to leading order by a change in the mean moisture convergence. Changes to the broad area of upper-level negative zonal stretching deformation, where transient eddies can become trapped and subsequently generate deep convection, support the notion that the SPCZ shift in the subtropics is tied to eddy forcing. Idealized experiments performed with an intermediate-level complexity model, the Quasi-Equilibrium Tropical Circulation Model (QTCM), suggest that the mid-Holocene change in rainfall in the SPCZ region as well as the equatorial Pacific is dominated by a change in the underlying SST. The tropical portion of the SPCZ is further remotely affected by the orbitally induced weakening of the Australian monsoon, even though this effect is weaker compared to the effect from SSTs.

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