Research ArticleCLIMATOLOGY

Trends in atmospheric patterns conducive to seasonal precipitation and temperature extremes in California

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Science Advances  01 Apr 2016:
Vol. 2, no. 4, e1501344
DOI: 10.1126/sciadv.1501344
  • Fig. 1 Observed October-May changes across the northeastern Pacific.

    (A) Mean trend in October-May 500-mb GPH over the northeastern Pacific and western North America, 1949–2015 (meters per year). (B) Contribution of lower tropospheric warming (thermal dilation) to observed October-May GPH trend (meters per year). (C) Mean trend in October-May SLP over the northeastern Pacific and western North America, 1949–2015 (millibars per year). Black box in (A) to (C) depicts the NPD. (D) Time series of mean October-May zonal gradient of 500-mb GPH in the NPD over four separate latitude bands (10−5 m/m). Units of reported trends are 10−8 m/(m*y). (E) Predictive skill of moderate to high pattern correlation using GPH and SLP. The quantity plotted is the percent of years that exhibited a pattern correlation of >0.4 with a particular extreme pattern and also experienced surface meteorological conditions of the correct sign (for example, low precipitation in a year that also had high correlation with one of the five dry patterns). Dashed horizontal line at 60% represents threshold for defining “increased likelihood” of a precipitation or temperature anomaly of the correct sign (as described in the text). Labels correspond to specific GPH/SLP patterns shown in matching figure panels in Figs. 3 to 6 [for example, “3D” corresponds to (D) in Fig. 3]. (F) Changes in the occurrence of GPH patterns that have moderate to high correlation (>0.4) with patterns of interest (that is, those associated with surface meteorological extremes). Left columns (striped fill) represent the 1949–1981 occurrence; right columns (solid fill) represent the 1982–2015 occurrence. Numbers in the gray horizontal rectangle under the column pairs indicate confidence (P values) that the change is statistically significant. (G) Same as in (H) but for SLP patterns.

  • Fig. 2 Observed October-May changes in zonal GPH gradient over the northeastern Pacific.

    Blue (red) points represent monthly values of the west-to-east GPH gradient averaged over the given range of latitudes from each year of the 1949–1981 (1982–2015) period. (A and B) Blue (red) curves represent monthly values of the west-to-east GPH gradient averaged over the given range of latitudes, averaged over 1949–1981 (1982–2015). The gray rectangles to the right of each panel show the change in subseasonal persistence of GPH gradients above the long-term average (months per year). Blue (red) columns represent mean values for 1949–1981 (1982–2015). (C) Change in extreme (±1 SD) 500-mb NPD GPH gradients between 1949–1981 and 1982–2015 over four separate latitude bands. Points above the dashed 1:1 line imply increasing frequency; points below 1:1 line imply decreasing frequency.

  • Fig. 3 Trends in California extreme dry patterns.

    (A to E) October-May 500-mb GPH anomaly patterns during California’s five driest cool-season periods between 1949 and 2015 (left column) and time series of pattern correlation between GPH/SLP in each specific year of interest (right column) and all other years. Horizontal dashed black lines highlight ±0.4 correlation thresholds used to define “moderate to high correlation” in this study. Maps shown are October-May 500-mb GPH anomalies for the given year (meters).

  • Fig. 4 Trends in California extreme wet patterns.

    (A to E) October-May 500-mb GPH anomaly patterns during California’s five wettest cool-season periods between 1949 and 2015 (left column) and time series of pattern correlation between GPH/SLP in each specific year of interest (right column) and all other years. Horizontal dashed black lines highlight ±0.4 correlation thresholds used to define moderate to high correlation in this study. Maps shown are October-May 500-mb GPH anomalies for the given year (meters).

  • Fig. 5 Trends in California extreme warm patterns.

    (A to E) October-May 500-mb GPH anomaly patterns during California’s five warmest detrended cool-season periods between 1949 and 2015 (left column) and time series of pattern correlation between GPH/SLP in each specific year of interest (right column) and all other years. Horizontal dashed black lines highlight ±0.4 correlation thresholds used to define moderate to high correlation in this study. Maps shown are October-May 500-mb GPH anomalies for the given year (meters).

  • Fig. 6 Trends in California extreme cool patterns.

    (A to E) October-May 500-mb GPH anomaly patterns during California’s five coolest detrended cool-season periods between 1949 and 2015 (left column) and time series of pattern correlation between GPH/SLP in each specific year of interest (right column) and all other years. Horizontal dashed black lines highlight ±0.4 correlation thresholds used to define moderate to high correlation in this study. Maps shown are October-May 500-mb GPH anomalies for the given year (meters).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/4/e1501344/DC1

    Fig. S1. Observed October-May changes across the northeastern Pacific.

    Fig. S2. Observed October-May changes in zonal GPH gradient over the northeastern Pacific.

    Fig. S3. Trends in California extreme dry patterns.

    Fig. S4. Trends in California extreme wet patterns.

    Fig. S5. Trends in California extreme warm patterns.

    Fig. S6. Trends in California extreme cool patterns.

    Fig. S7. Change in frequency of high-correlation years using GPH.

    Fig. S8. A comprehensive summary of extreme pattern trend results for analysis using linearly detrended 500-mb GPH data (columns labeled “DT”) and using non-detrended GPH data (columns labeled “NDT”).

    Fig. S9. Time series of pattern correlation between GPH pattern in each specific year of interest and all other years using linearly detrended GPH data.

    Fig. S10. Observed trends in GPH, precipitation, and temperature.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Observed October-May changes across the northeastern Pacific.
    • Fig. S2. Observed October-May changes in zonal GPH gradient over the northeastern Pacific.
    • Fig. S3. Trends in California extreme dry patterns.
    • Fig. S4. Trends in California extreme wet patterns.
    • Fig. S5. Trends in California extreme warm patterns.
    • Fig. S6. Trends in California extreme cool patterns.
    • Fig. S7. Change in frequency of high-correlation years using GPH.
    • Fig. S8. A comprehensive summary of extreme pattern trend results for analysis using linearly detrended 500-mb GPH data (columns labeled “DT”) and using non-detrended GPH data (columns labeled “NDT”).
    • Fig. S9. Time series of pattern correlation between GPH pattern in each specific year of interest and all other years using linearly detrended GPH data.
    • Fig. S10. Observed trends in GPH, precipitation, and temperature.

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