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- Author or Editor: Andrew M. Lorrey x
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Abstract
Tropical cyclones (TCs) produce extreme winds, large waves, storm surges, intense rainfall, and flooding and account for almost 75% of natural disasters across the southwest Pacific (SWP) region. The island nations and territories across the SWP rely on seasonal TC outlooks for insights into possible risks for the coming TC season. Launched in July 2020, the Long-Range Tropical Cyclone Outlook for the Southwest Pacific (TCO-SP) provides deterministic (frequency) and probabilistic (likelihood) TC outlooks for 12 subregional and island-scale locations up to 4 months (July) before the start of the SWP TC season (November–April). Following TCO-SP’s first season of operation, this study (i) outlines the process of generating and communicating TCO-SP outlooks, (ii) provides a postseason validation of TCO-SP performance on the 2020/21 SWP TC season, and (iii) reports on the results of a questionnaire used to determine end-user needs and user-perceived usefulness of TCO-SP. Postseason validation indicates that TCO-SP successfully predicted a near-normal SWP TC season. Island- and regional-scale guidance also performed well, with an average skill score of 54% across all regions. Analysis of responses to a TCO-SP questionnaire revealed a diverse and global user base that indicate the core features of TCO-SP (island-scale/regional-scale outlooks, regular monthly updates, and an outlook lead time up to 4 months before the start of the TC season) are particularly useful. TCO-SP will continue to innovate to deliver reliable and trusted TC outlooks with a goal to reduce disaster risk and increase resilience across the SWP region.
Abstract
Tropical cyclones (TCs) produce extreme winds, large waves, storm surges, intense rainfall, and flooding and account for almost 75% of natural disasters across the southwest Pacific (SWP) region. The island nations and territories across the SWP rely on seasonal TC outlooks for insights into possible risks for the coming TC season. Launched in July 2020, the Long-Range Tropical Cyclone Outlook for the Southwest Pacific (TCO-SP) provides deterministic (frequency) and probabilistic (likelihood) TC outlooks for 12 subregional and island-scale locations up to 4 months (July) before the start of the SWP TC season (November–April). Following TCO-SP’s first season of operation, this study (i) outlines the process of generating and communicating TCO-SP outlooks, (ii) provides a postseason validation of TCO-SP performance on the 2020/21 SWP TC season, and (iii) reports on the results of a questionnaire used to determine end-user needs and user-perceived usefulness of TCO-SP. Postseason validation indicates that TCO-SP successfully predicted a near-normal SWP TC season. Island- and regional-scale guidance also performed well, with an average skill score of 54% across all regions. Analysis of responses to a TCO-SP questionnaire revealed a diverse and global user base that indicate the core features of TCO-SP (island-scale/regional-scale outlooks, regular monthly updates, and an outlook lead time up to 4 months before the start of the TC season) are particularly useful. TCO-SP will continue to innovate to deliver reliable and trusted TC outlooks with a goal to reduce disaster risk and increase resilience across the SWP region.
Abstract
The new South Pacific Enhanced Archive for Tropical Cyclones (SPEArTC) dataset provides an opportunity to develop a more complete climatology of tropical cyclones (TCs) in the southwest Pacific. Here, spatial patterns and characteristics of TCs for the 41-yr period beginning with the 1969/70 season are related to phases of the El Niño–Southern Oscillation (ENSO), taking into account the degree of ocean–atmosphere coupling. Twentieth-century reanalysis data and the coupled ENSO index (CEI) were used to investigate TC genesis areas and climate diagnostics in the extratropical transition (ETT) region at and south of 25°S during different CEI ENSO phases. This is the first study looking at CEI-based ENSO phases and the more detailed relationship of TCs to the coupling of the ocean and atmosphere during different ENSO phases. Consistent with previous findings, positive relationships exist among TCs, sea surface temperature, and atmospheric circulation. A statistically significant greater frequency of major TCs was found during the latter half of the study period (1991–2010) compared to the 1970–90 period, again consistent with the findings of other studies. Also found were significant and consistent linkages highlighting the interplay of TCs and sea surface temperature (SSTs) in the southwest Pacific basin west of 170°E and a closer connection to atmospheric circulation east of 170°E. Moreover, this study demonstrates subtle differences between a fully coupled El Niño or La Niña and atmospheric- or ocean-dominated phases, or neutral conditions.
Abstract
The new South Pacific Enhanced Archive for Tropical Cyclones (SPEArTC) dataset provides an opportunity to develop a more complete climatology of tropical cyclones (TCs) in the southwest Pacific. Here, spatial patterns and characteristics of TCs for the 41-yr period beginning with the 1969/70 season are related to phases of the El Niño–Southern Oscillation (ENSO), taking into account the degree of ocean–atmosphere coupling. Twentieth-century reanalysis data and the coupled ENSO index (CEI) were used to investigate TC genesis areas and climate diagnostics in the extratropical transition (ETT) region at and south of 25°S during different CEI ENSO phases. This is the first study looking at CEI-based ENSO phases and the more detailed relationship of TCs to the coupling of the ocean and atmosphere during different ENSO phases. Consistent with previous findings, positive relationships exist among TCs, sea surface temperature, and atmospheric circulation. A statistically significant greater frequency of major TCs was found during the latter half of the study period (1991–2010) compared to the 1970–90 period, again consistent with the findings of other studies. Also found were significant and consistent linkages highlighting the interplay of TCs and sea surface temperature (SSTs) in the southwest Pacific basin west of 170°E and a closer connection to atmospheric circulation east of 170°E. Moreover, this study demonstrates subtle differences between a fully coupled El Niño or La Niña and atmospheric- or ocean-dominated phases, or neutral conditions.
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.
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.
Abstract
The stationarity of relationships between local and remote climates is a necessary, yet implicit, assumption underlying many paleoclimate reconstructions. However, the assumption is tenuous for many seasonal relationships between interannual variations in the El Niño–Southern Oscillation (ENSO) and the southern annular mode (SAM) and Australasian precipitation and mean temperatures. Nonstationary statistical relationships between local and remote climates on the 31–71-yr time scale, defined as a change in their strength and/or phase outside that expected from local climate noise, are detected on near-centennial time scales from instrumental data, climate model simulations, and paleoclimate proxies.
The relationships between ENSO and SAM and Australasian precipitation were nonstationary at 21%–37% of Australasian stations from 1900 to 2009 and strongly covaried, suggesting common modulation. Control simulations from three coupled climate models produce ENSO-like and SAM-like patterns of variability, but differ in detail to the observed patterns in Australasia. However, the model teleconnections also display nonstationarity, in some cases for over 50% of the domain. Therefore, nonstationary local–remote climatic relationships are inherent in environments regulated by internal variability. The assessments using paleoclimate reconstructions are not robust because of extraneous noise associated with the paleoclimate proxies.
Instrumental records provide the only means of calibrating and evaluating regional paleoclimate reconstructions. However, the length of Australasian instrumental observations may be too short to capture the near-centennial-scale variations in local–remote climatic relationships, potentially compromising these reconstructions. The uncertainty surrounding nonstationary teleconnections must be acknowledged and quantified. This should include interpreting nonstationarities in paleoclimate reconstructions using physically based frameworks.
Abstract
The stationarity of relationships between local and remote climates is a necessary, yet implicit, assumption underlying many paleoclimate reconstructions. However, the assumption is tenuous for many seasonal relationships between interannual variations in the El Niño–Southern Oscillation (ENSO) and the southern annular mode (SAM) and Australasian precipitation and mean temperatures. Nonstationary statistical relationships between local and remote climates on the 31–71-yr time scale, defined as a change in their strength and/or phase outside that expected from local climate noise, are detected on near-centennial time scales from instrumental data, climate model simulations, and paleoclimate proxies.
The relationships between ENSO and SAM and Australasian precipitation were nonstationary at 21%–37% of Australasian stations from 1900 to 2009 and strongly covaried, suggesting common modulation. Control simulations from three coupled climate models produce ENSO-like and SAM-like patterns of variability, but differ in detail to the observed patterns in Australasia. However, the model teleconnections also display nonstationarity, in some cases for over 50% of the domain. Therefore, nonstationary local–remote climatic relationships are inherent in environments regulated by internal variability. The assessments using paleoclimate reconstructions are not robust because of extraneous noise associated with the paleoclimate proxies.
Instrumental records provide the only means of calibrating and evaluating regional paleoclimate reconstructions. However, the length of Australasian instrumental observations may be too short to capture the near-centennial-scale variations in local–remote climatic relationships, potentially compromising these reconstructions. The uncertainty surrounding nonstationary teleconnections must be acknowledged and quantified. This should include interpreting nonstationarities in paleoclimate reconstructions using physically based frameworks.
Abstract
Instrumental meteorological measurements from periods prior to the start of national weather services are designated “early instrumental data.” They have played an important role in climate research as they allow daily to decadal variability and changes of temperature, pressure, and precipitation, including extremes, to be addressed. Early instrumental data can also help place twenty-first century climatic changes into a historical context such as defining preindustrial climate and its variability. Until recently, the focus was on long, high-quality series, while the large number of shorter series (which together also cover long periods) received little to no attention. The shift in climate and climate impact research from mean climate characteristics toward weather variability and extremes, as well as the success of historical reanalyses that make use of short series, generates a need for locating and exploring further early instrumental measurements. However, information on early instrumental series has never been electronically compiled on a global scale. Here we attempt a worldwide compilation of metadata on early instrumental meteorological records prior to 1850 (1890 for Africa and the Arctic). Our global inventory comprises information on several thousand records, about half of which have not yet been digitized (not even as monthly means), and only approximately 20% of which have made it to global repositories. The inventory will help to prioritize data rescue efforts and can be used to analyze the potential feasibility of historical weather data products. The inventory will be maintained as a living document and is a first, critical, step toward the systematic rescue and reevaluation of these highly valuable early records. Additions to the inventory are welcome.
Abstract
Instrumental meteorological measurements from periods prior to the start of national weather services are designated “early instrumental data.” They have played an important role in climate research as they allow daily to decadal variability and changes of temperature, pressure, and precipitation, including extremes, to be addressed. Early instrumental data can also help place twenty-first century climatic changes into a historical context such as defining preindustrial climate and its variability. Until recently, the focus was on long, high-quality series, while the large number of shorter series (which together also cover long periods) received little to no attention. The shift in climate and climate impact research from mean climate characteristics toward weather variability and extremes, as well as the success of historical reanalyses that make use of short series, generates a need for locating and exploring further early instrumental measurements. However, information on early instrumental series has never been electronically compiled on a global scale. Here we attempt a worldwide compilation of metadata on early instrumental meteorological records prior to 1850 (1890 for Africa and the Arctic). Our global inventory comprises information on several thousand records, about half of which have not yet been digitized (not even as monthly means), and only approximately 20% of which have made it to global repositories. The inventory will help to prioritize data rescue efforts and can be used to analyze the potential feasibility of historical weather data products. The inventory will be maintained as a living document and is a first, critical, step toward the systematic rescue and reevaluation of these highly valuable early records. Additions to the inventory are welcome.
