Title:
Kawasaki Disease and ENSO-driven wind circulation
Authors:
Joan Ballester (1), Jane C. Burns (2), Dan Cayan (3), Yosikazu Nakamura (4), Ritei
Uehara (4), Xavier Rodó (1,5)
Affiliations:
(1) Institut Català de Ciències del Clima (IC3), Barcelona, Catalonia, Spain
(2) Department of Pediatrics, Rady Children’s Hospital San Diego and UCSD, La Jolla,
CA
(3) Climate, Atmospheric Science, and Physical Oceanography, Scripps Institution of
Oceanography, UCSD and Water Resources Discipline, US Geological Survey, La Jolla,
CA
(4) Department of Public Health, Jichi Medical University, Tochigi, Japan
(5) Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Catalonia,
Spain
Corresponding author (present address):
Joan Ballester
California Institute of Technology (Caltech)
1200 E California Blvd, Pasadena, CA 91125, US
Mail Code: 131-24
Tel.: +1 626-395-8703
Email: joanballester@caltech.edu
Key points:
Kawasaki Disease is the most common cause of acquired heart disease in children
Kawasaki Disease may be triggered by a windborne agent
El Niño-Southern Oscillation is associated with enhanced Kawasaki Disease
Index terms:
3309 Climatology
3339 Ocean/atmosphere interactions
3373 Tropical dynamics
4215 Climate and interannual variability
4522 ENSO
Keywords:
Kawasaki Disease
El Niño-Southern Oscillation
El Niño and La Niña
Tropospheric winds
Tropical-extratropical teleconnections
Surface ocean conditions
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Supplementary Material
Tropospheric mechanism explaining the seasonality and epidemics of KD
Rodó et al. (2011) described the relationship between the nearly synchronized
winter peak of KD in Japan and San Diego and the wintertime tropospheric “duct”
sweeping from continental Asia to the western north Pacific (green box in Supplementary
Figure 1). The close timing of the seasonal peak in both sites, as well as its synchrony
with both strong low-level northwesterly winds in Japan and intense zonal winds
throughout the subtropical north Pacific, suggested that the causal agent of KD is
transported from continental Asia to Japan by low-level air currents, and across the north
Pacific to the United States by strong zonal winds developing in the upper troposphere.
This tropospheric winter window coincided with the growing phase of 3 dramatic
nationwide epidemics in Japan (Supplementary Figure 2), by far the largest epidemic
events ever recorded worldwide. Thus, the number of cases rapidly mounted in autumn
all over the country when winds turned northwest in direction, and suddenly started to
decrease in spring when winds again shifted and blew from the south.
KD time series in Japan and San Diego
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The Japanese KD time series is derived from the biannual national surveillance of
all hospitals in Japan with more than 100 beds. Data corresponds to 16 separate
questionnaire surveys of Japanese hospitals for the period 1970–2010, providing the most
comprehensive record of KD cases in the world. Patient date of hospitalization and
prefecture of residence are recorded for each subject in the time series, which contains
271,415 cases until 2010 (141,677 cases during the period 1987-2006 considered here).
The time series for hospital admissions in San Diego was assembled from the
database of the Kawasaki Disease Research Center at the University of California for the
period 1994–2008. It derives from active surveillance for KD cases hospitalized at Rady
Children’s Hospital San Diego, a tertiary referral center that cares for more than 90% of
the acute KD cases in San Diego County.
Time series are formed by KD patients, the date being that of hospital admission
recorded for all subjects. For subjects with multiple admissions, only the first
hospitalization date was used. To provide uniform assessment among sites, the date of
admission was used as a surrogate for the date of fever onset, even though for comparison
with other studies, the average day of KD diagnosis is normally centered on the 5th day
of fever. However, analyses were reproduced with calculated dates of fever onset and
results did not differ (p < 0.001, t-test).
Filtering of the interannual component of KD time series
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An eigendecomposition analysis applied to the data covariance matrix of monthly
KD time series in Japan and San Diego was used to partition signal contributions by
frequency, with the aid of adaptative nonparametric functions (Elsner and Tsonis 1996).
An embedding dimension or order of the decomposition of 40 was selected, as it allows a
proper characterization of those signals with period larger than the annual cycle
(Dettinger et al. 1995). In this study, only principal components coming from significant
eigenvalues that captured interannual frequencies were kept for further reconstruction
(black line in Figures 1a,d). For comparison, a data tapering window procedure to
minimize spectral leakage was applied to each series to remove spurious results and
maximize both the decomposition and the reconstruction. Find a complete description of
the data sources and further details of the filtering procedure in Rodó et al. (2011).
Significance level of composite anomalies
The significance level of the interannual ocean and atmosphere anomaly maps
(Figure 2 and Supplementary Figure 4) was computed using a bootstrap method (Efron
and Tibshirani 1993), which was especially designed to evaluate data whose degrees of
freedom are reduced by low-pass filters and the averaging of small samples of events in
the composites. The reference probability distribution function was locally computed by
means of 10000 white-noise time series, which were then tested against an autoregressive
process of order 1 having the same mean, standard deviation, and temporal one-lag
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autocorrelation value as the interannual grid-point time series of the variable tested. Find
further details in Ballester et al. (2011).
References
Ballester J, Rodríguez-Arias MA, Rodó X. A new extratropical tracer describing
the role of the western Pacific in the onset of El Niño: Implications for ENSO
understanding and forecasting. Journal of Climate 24, 1425-1437 (2011).
Dettinger MD, Strong CM, Weibel W, Ghil M, Yiou P. Software for singular
spectrum analysis of noisy time series. Eos, Transactions, American Geophysical Union
76, 12 (1995).
Efron B, Tibshirani R. Introduction to the Bootstrap. Chapman and Hall, 436 pp
(1993).
Elsner JB, Tsonis AA. Singular Spectrum Analysis: A New Tool in Time Series
Analysis. Plenum Press, 164 pp (1996).
Rodó X, Ballester J, Cayan D, Melish ME, Nakamura Y, Uehara R, Burns JC.
Association of Kawasaki disease with tropospheric wind patterns. Nature Scientific
Reports 1, 152 (2011).
Figure Captions
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Supplementary Figure 1. Mean seasonal cycle of surface (a-d), 700hPa (e-h)
and 300hPa (i-l) winds (m/s) for 1994-2008.
Arrows correspond to horizontal winds, and the shading to the zonal component
only. The green box depicts the zonal path connecting the Asian continent with Japan and
the western coast of the United States, which is strongest at all vertical levels in boreal
winter (DJF).
Supplementary Figure 2. Major epidemics of KD in Japan (1978/79, 1981/82,
1985/86).
Panels a,d,g and c,f,i depict the time average of surface winds (arrows, m/s) and
the change in KD at the prefecture level (colored dots, cases per million) for the
increasing (autumn and winter) and decreasing (spring and summer) phases of the
epidemics shown in red and blue in panels b,e,h, respectively.
Supplementary Figure 3. Ocean configuration for the individual interannual
peaks of KD in Japan (a-c) and San Diego (d-f).
Panels a and d depict the correspondence between equatorial surface ocean
warming and the standardized (unitless) interannual component of KD for the peaks in
Figures 1a,d for Japan and San Diego, respectively. Equatorial warming is here depicted
as the longitudinal range (horizontal lines) and maximum (dots) of positive standardized
interannual anomalies of equatorially-averaged (5S-5N) sea surface temperature. From
left to right, map columns show the standardized (unitless) interannual anomalies of sea
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surface temperature for the peaks shown in red and pink in Figure 1a for Japan, and in red
and pink in Figure 1d for San Diego.
Supplementary Figure 4. Ocean-atmosphere mean composites for the
interannual peaks of KD in Japan (a-f) and San Diego (g-r).
From left to right, columns show the standardized (unitless) interannual anomalies
for the peaks shown in red and pink in Figure 1a for Japan, and in red and pink in Figure
1d for San Diego. See the individual events in Supplementary Figures 3b,c, 4b,c,
respectively. Maps correspond to the composites for sea surface temperature (shading and
contours in a,d,g,m), 500hPa geopotential height (shading and contours in j,p) and
500hPa winds (arrows in j,p). White contours depict shaded areas in the maps with
significant anomalies (p < 0.05). Composite anomalies of tropospheric winds along zonal
(b,e,h,k,l,n,q,r) and meridional (c,f,i,o) cross sections (see green and brown boxes in the
corresponding column map) are depicted in the two bottom rows, in which the shading
corresponds to the meridional (positive means northwards) or zonal (positive means
eastwards) component, respectively.
Supplementary Figure 5. Same as Figures 2e-j for the ocean-atmosphere
composites in San Diego, but using the same criterion for the selection of the peaks
than in Rodó et al. (2011).
The seven peaks reaching the +0.75 standard deviation criterion in the
reconstructed interannual component were included in this case in the ocean-atmosphere
composites. Two events were thus added: the red peak in 1994/95 (KD = +0.79σ) and the
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pink peak in 2005/06 (KD = +0.98σ). This figure shows that results are not sensitive to
the choice of the threshold.
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