Research ArticleCLIMATOLOGY

Reconstructed storm tracks reveal three centuries of changing moisture delivery to North America

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Science Advances  07 Jun 2017:
Vol. 3, no. 6, e1602263
DOI: 10.1126/sciadv.1602263
  • Fig. 1 Circulation-based tree-ring site development and additional tree-ring site locations.

    (A) Black circles show locations of seven new Pinus ponderosa (Ponderosa pine) tree-ring sites surrounding the Columbia River Basin in Washington, USA. We used a circulation-based field sampling strategy for developing chronologies in regions with contrasting responses to storm-track patterns. Map background shows cool-season precipitation anomalies in instrumental-period El Niño years when changing storm-track trajectories lead to reduced orographic effects and a contrasting climate response across the PNW. Precipitation data are from the Parameter-Elevation Regressions on Independent Slopes Model data set. (B) Chronologies from the ITRDB that maintain an expressed population signal of >0.85 over the time period of 1693 to 1995 CE and were tested for inclusion as predictors in the storm-track position and intensity reconstructions.

  • Fig. 2 Reconstruction of cool-season storm-track position from 1693 to 1995 CE.

    (A) Cool-season (October to March) observed (thin green) and reconstructed (thin gray) storm-track latitude at 124°W longitude with a 22-year moving average (thick green and black) to highlight longer-term variability at an important frequency band. (B) Cool-season (October to March) observed (thin brown) and reconstructed (thin gray) storm-track intensity at 124°W longitude with a 12-year moving average (thick brown and black) to highlight longer-term variability at an important frequency band. (C) Storm-track latitude (solid green) and intensity (solid brown) averaged over 20-year periods throughout the reconstruction. The final 19-year period (green and brown outlines) is based on instrumental, rather than reconstructed, data.

  • Fig. 3 Reconstructed storm tracks during years with anomalous precipitation patterns.

    SPI reconstruction (37) grid cells in the PNW representing the windward and leeward response regions of the Cascades (see fig. S6) were used to calculate four patterns of interest over the period of 1693 to 1995 CE: (A) both windward and leeward sides anomalously dry (75% of grid cells in each category with SPI of ≤−0.8), (B) leeward side dry (75% of grid cells with SPI of <0) and windward side wet (75% of grid cells with SPI of >0), (C) leeward side wet (75% of grid cells with SPI of >0) and windward side dry (75% of grid cells with SPI of <0), and (D) both windward and leeward anomalously wet (75% of grid cells in each category with SPI of ≥0.8). Storm tracks were smoothed with a robust loess filter. See table S1 for additional data on reconstructed storm tracks for each pattern.

  • Fig. 4 SPI and storm track in La Niña and El Niño years from 1728 to 1995 CE.

    Composites of reconstructed SPI (37) (A and B) and yearly storm tracks smoothed with a robust loess filter (C and D) during La Niña (A and C) and El Niño (B and D) years, determined using the annual NINO3.4 SST reconstructed from tropical Pacific coral and ice core records (30). Years were characterized as El Niño or La Niña based on ±1 SD from mean conditions over the annual period beginning the January before the reconstructed storm-track cool season (for example, storm track from October 1727 to March 1728 associated with NINO3.4 from January to December 1727).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/6/e1602263/DC1

    fig. S1. Tree-ring chronologies for seven sites in the U.S. PNW.

    fig. S2. Validation statistics for the storm-track reconstruction at each longitude.

    fig. S3. Delineation of the storm track in an example year (1988).

    fig. S4. Extremes in latitude and intensity in reconstructed storm tracks over the reconstruction period of 1693 to 1995 CE.

    fig. S5. Spectral power in the storm-track reconstructions.

    fig. S6. Grid cells representing windward and leeward regions across the Cascade Range.

    fig. S7. Storm track in La Niña and El Niño years based on an alternative ENSO reconstruction from 1693 to 1995 CE.

    fig. S8. Distribution of reconstructed storm-track position in La Niña and El Niño years.

    fig. S9. Distribution of reconstructed storm-track intensity in La Niña and El Niño years.

    table S1. Reconstructed storm-track latitude and intensity in years with anomalous precipitation patterns.

    table S2. Reconstructed storm-track latitude and intensity in La Niña and El Niño years based on multiple ENSO proxy reconstructions.

    References (44, 45, 62, 63)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Tree-ring chronologies for seven sites in the U.S. PNW.
    • fig. S2. Validation statistics for the storm-track reconstruction at each longitude.
    • fig. S3. Delineation of the storm track in an example year (1988).
    • fig. S4. Extremes in latitude and intensity in reconstructed storm tracks over the reconstruction period of 1693 to 1995 CE.
    • fig. S5. Spectral power in the storm-track reconstructions.
    • fig. S6. Grid cells representing windward and leeward regions across the Cascade Range.
    • fig. S7. Storm track in La Niña and El Niño years based on an alternative ENSO reconstruction from 1693 to 1995 CE.
    • fig. S8. Distribution of reconstructed storm-track position in La Niña and El Niño years.
    • fig. S9. Distribution of reconstructed storm-track intensity in La Niña and El Niño years.
    • table S1. Reconstructed storm-track latitude and intensity in years with anomalous precipitation patterns.
    • table S2. Reconstructed storm-track latitude and intensity in La Niña and El Niño years based on multiple ENSO proxy reconstructions.
    • References (44, 45, 62, 63)

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