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C. F. Ropelewski and M. S. Halpert

Abstract

The relationships are examined between precipitation and the high index phase of the Southern Oscillation (SO) for 19 regions of the globe which have documented low SO index-precipitation relationships (Ropelewski and Halpert 1986, 1987). The study reveals that 15 of these regions also show evidence of characteristic precipitation anomalies during the high index phase of the SO. In each of the regions, the high SO index-precipitation relationships show the opposite sign of those documented for the low index. These precipitation relationships were consistent, holding for over 70% of the high SO index years, and statistically significant. In particular, the high index phase of the SO is associated with enhanced precipitation for the monsoons of India and northern Australia as well as for the rainy seasons in northeastern South America and southeastern Africa. High SO index precipitation was found to be less than median in the central Pacific, Minicoy-Sri Lanka, eastern equatorial Africa, the Gulf of Mexico and northern Mexico region, and southeastern South America. The seasons which showed high SO index-precipitation relationship were almost identical to the masons associated with the low index in 13 of the 15 high SO index regions. Thus to a first approximation, this study suggests that the sign of the precipitation anomaly for these regions is linearly related to the phase of the SO. Since there am 25 low index and 19 high index years in the 109 yr analysis period, from 1875 to 1983, these results further suggest that, for over 40% of the years precipitation may be classified and perhaps predicted on the basis of the extreme SO phase.

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C. F. Ropelewski and M. S. Halpert

Abstract

We investigate the “typical” global and large-scale regional precipitation patterns that are associated with the El Niño/Southern Oscillation (ENSO). Monthly precipitation time series from over 1700 stations are analyzed using an empirical method designed to identify regions of the globe that have precipitation variations associated with ENSO. Monthly mean ranked precipitation composites are computed over idealized 2-year ENSO episodes for all stations that include data for at least five ENSOs. The amplitude and phase of the Arm harmonic fitted to the 24-month composite values are plotted in the form of a vector for each station. When plotted on a global map, these vectors reveal both the regions of spatially coherent ENSO-related precipitation and the phase of this signal in relation to the evolution of the composite episode. Time cries of precipitation for the coherent regions identified in the harmonic vector map are examined to determine the magnitudes of the ENSO-related precipitation and the percentages of the time the identified relationship actually occurred in conjunction with ENSO episodes.

This study expands previous results by placing the regional precipitation relationships into a global framework and by providing a consistent methodology for the definition of the geographical regions and the temporal phase of ENSO-related precipitation. In addition to the Pacific Ocean basin where precipitation patterns could be directly related to the ENSO, several other regions, which showed consistent ENSO-related precipitation, were identified. Specifically, four regions in Australia, two regions each in North America South America, the Indian subcontinent, and Africa and one region in Central America were all found to have coherent ENSO-related precipitation. In most of thew regions, the “season” of ENSO-related precipitation was found to be in phase with the normal annual precipitation cycle. Time series of area-averaged precipitation for the appropriate “seasons” show departures consistent with the composites occurring for at 1east 80% of the ENSO events in almost every region. The analysis further indicates that variations in precipitation related to ENSO occur as early as April of the composite episode through May of the following year.

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Michael S. Halpert and Thomas M. Smith

Abstract

No abstract available

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C. F. Ropelewski and M. S. Halpert

Abstract

This paper describes an investigation of the “typical” North American precipitation and temperature patterns associated with the El Niño/Southern Oscillation (ENSO). Monthly surface temperature and precipitation data are analyzed using a method designed to identify regions of the globe that have responses associated with ENSO. Monthly composites, covering idealized two-year ENSO episodes, are computed for temperature and precipitation at all stations with data spanning seven or more ENSO events. The firm harmonic is extracted from the 24 monthly composite values and plotted in the form of a two-year harmonic dial vector. When plotted on a map of North America, these vectors reveal both the regions of coherent response and the phase of the responses with respect to the evolution of the ENSO episode. Time series of temperature and precipitation for the regions identified in the harmonic vector maps are examined to determine the magnitudes of the responses and the percentage of the time that the identified responses actually occurred in association with the ENSO events. The temperature anomalies are expressed in terms of standardized departures, while precipitation departures are expressed as percentiles of the appropriate gamma distributions, fitted to the entire data record.

The analysis shows that above normal precipitation was associated with ENSO in 18 out of 22 cases (81%)in the “season” starting with October of the ENSO year to March of the following year for an area of North America that includes parts of the southeastern United States and northern Mexico. Above normal precipitation was also observed in the Great Basin area of the western United States in 9 out of 11 cases (81%) for the April through October “season” during ENSO years. No high latitude precipitation signals were indicated by this analysis. Areas of Alaska and western Canada experienced positive temperature anomalies in 17 out of 21 ENSO episodes (81%) during the “season” defined by December of the ENSO year through the following March. Parts of the southeastern United States near the Gulf of Mexico were found to have negative temperature anomalies associated with 20 out of 25 ENSO episodes (80%) for the “season” October of the ENSO year through the following March.

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J. E. Janowiak, C. F. Ropelewski, and M. S. Halpert

Abstract

An objective method to identify and track significant global precipitation anomalies on time scales of a month or longer is presented. The technique requires current observations of monthly precipitation amounts for each station and long term (20 or more years) monthly precipitation histories. Tests indicate that the technique compares favorably with the well-known Palmer Drought Severity Index (PDSI) and Crop Moisture Index (CMI) in the United States. Since monthly precipitation data are readily available in a near real-time framework, this method makes an automated, global precipitation anomaly monitoring system possible.

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C. F. Ropelewski, J. E. Janowiak, and M. S. Halpert

Abstract

No abstract available.

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Howard J. Diamond, Carl J. Schreck III, Emily J. Becker, Gerald D. Bell, Eric S. Blake, Stephanie Bond, Francis G. Bringas, Suzana J. Camargo, Lin Chen, Caio A. S. Coelho, Ricardo Domingues, Stanley B. Goldenberg, Gustavo Goni, Nicolas Fauchereau, Michael S. Halpert, Qiong He, Philip J. Klotzbach, John A. Knaff, Michelle L'Heureux, Chris W. Landsea, I.-I. Lin, Andrew M. Lorrey, Jing-Jia Luo, Kyle MacRitchie, Andrew D. Magee, Ben Noll, Richard J. Pasch, Alexandre B. Pezza, Matthew Rosencrans, Michael K. Tippet, Blair C. Trewin, Ryan E. Truchelut, Bin Wang, Hui Wang, Kimberly M. Wood, John-Mark Woolley, and Steven H. Young
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Stephen Baxter, Gerald D Bell, Eric S Blake, Francis G Bringas, Suzana J Camargo, Lin Chen, Caio A. S Coelho, Ricardo Domingues, Stanley B Goldenberg, Gustavo Goni, Nicolas Fauchereau, Michael S Halpert, Qiong He, Philip J Klotzbach, John A Knaff, Michelle L'Heureux, Chris W Landsea, I.-I Lin, Andrew M Lorrey, Jing-Jia Luo, Andrew D Magee, Richard J Pasch, Petra R Pearce, Alexandre B Pezza, Matthew Rosencrans, Blair C Trewin, Ryan E Truchelut, Bin Wang, H Wang, Kimberly M Wood, and John-Mark Woolley
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