Effect of sea surface temperature on precipitation

The Boreal Summer Intra-Seasonal Oscillation (BSISO) is the propagation of long lasting cloudy condition from

equatorial region. The BSISO has been studied to understand the Asian summer monsoon.

Fig. 9 study region and domain for selecting

SST anomaly (black rectangle)

Effect of sea surface temperature on precipitation variability in East Asia induced by the Boreal Summer Intra-seasonal OscillationDeokyoung Han (Master course student)

Graduate School of Environmental Science, Hokkaido University

Result

BSISO index and its relationship with precipitation

Discussion

Purpose of the research

Conclusion

Hoyos and webster (2007)

Phase 1 Phase 2 Phase 3 Phase 4


Fig. 15 Difference between SST higher and SST lower composites about potential temperature anomaly (color, K) and moisture flux (line, 102 g kg-1 m s-1 )

of 25-35N latitude average associated with the BSISO phases. Solid (Dotted) lines indicate westerly (easterly) moisture flux



Fig. 16 Difference between SST higher and SST lower composites about moisture amount anomaly (color, hPa) and zonal wind anomaly

(line, m s-1 ) of 25-35N latitude average associated with the BSISO phases. Solid (Dotted) lines indicate westerly (easterly) wind anomaly

Weather

Intra-Seasonal

Oscillation

Seasonal

variation

daily scale

weekly scale

monthly scale i.e. summer

i.e. frequent

stationary front

i.e. heavy precipitation

in few days

Fig. 3 Time scale of atmospheric phenomena

Indian summer monsoon

East Asian summer monsoon

m / s

mm / day

Fig. 4 Climatology of precipitation and surface wind for MJJA during 2000-2019

Lee et al. (2017)

EEOF analysis of filtered outgoing longwave radiation can extract the signal of the BSISO.

Phase diagram of the BSISO PCs indicates the approximate location of active convection (Fig. 5, 6).

Kikuchi. (2012)

Fig. 5 Spatial and temporal pattern of 25-90-day filtered OLR for JJA.

0 day indicates the appearance of convection in left-bottom panel

The northward propagation of BSISO in Indian Ocean influenced precipitation in Indian

peninsula (Fig. 7). When the phase of 30-60-day BSISO was 3 to 5, there was positive

precipitation anomaly in East Asia with respect to non-BSISO cases (Fig. 8).

Fig. 7 Schematic diagram of the development of precipitation over the BoB associated

with the ISO; (a) genesis of the ISO and (b) northward propagation of the ISO. The

darker (clearer) shading indicates warmer (colder) SST than usual

Fig. 8 Composites of precipitation anomaly in the phase 4

of 30-60-day BSISO respect to the non-BSISO cases

Data & Method

There are few researches that SST has an effect on the precipitation variability

associated with the BSISO in East Asia.

This research is to explain the precipitation variability associated with the

BSISO would be different upon SST over East Asia.

Table. 1 Dataset of the research

Open source of PCs of BSISO (Kikuchi et al. 2012) was used to define time series and each

phase of the BSISO. Daily area-averaged SST anomalies above (under) +0.5 (-0.5) were

collected to describe the effect of SST enough.

Fig. 11 Snap shots of BSISO events

Time progresses from top to bottom

Phase 4

Phase 6

Phase 8

Phase 4

Phase 2

Fig. 12 OLR anomalies (color, unit W /m2) & UV850 anomalies (vector, m /s) for JJASO during 2000-2019 associated with each BSISO phase. Dots and vectors indicate over 95% confidence level. The number of BSISO events is given in each phase

Fig. 13 Composite of 25-90-day filtered precipitation anomalies (color, mm/day) for JJASO during 2000-2019 associated

with the BSISO phases. Dots indicate over 95% confidence level. The number of BSISO events is given in each phase

Phase 1 (246) Phase 2 (225) Phase 3 (251) Phase 4 (239)




Area-averaged SST anomaly > + 0.5: enough to describe the effect of positive SST anomaly

Area-averaged SST anomaly < - 0.5: enough to describe the effect of negative SST anomaly

Fig. 14 Composite of 25-90-day filtered precipitation anomalies (mm/day) for each phase associated with SST anomalies in East China

Sea and western North Pacific. Color indicates over 95% confidence level. The number of BSISO events is given in each phase

Positive SST anomaly might induce zonally elongated positive precipitation anomaly during BSISO phase 4, 6 in East Asia (Fig. 14). BSISO phase 4, 6 are corresponding to the anti-cyclonic circulation in western North Pacific (Fig. 12)

When the anti-cyclonic circulation was located in western North-Pacific like BSISO phase 3, 4, 6 (Fig. 12), warm and humid westerly wind might trigger zonally elongated precipitation if SST is higher near East Asia (Fig. 15, 16).

SST anomaly

> + 0.5SST anomaly

< - 0.5

BSISO Phase 3-6: warmer potential temperature and strong westerly moisture flux near 120-130E

BSISO Phase 3, 4, 6: larger moisture amount and corresponding westerly wind anomaly near 120-130E

▪ Zonally elongated precipitation appeared when the anti-cyclonic circulation in western North Pacific was located and SST was higher near East Asia.

▪ Westerly wind corresponding to synoptic circulation and humid air from higher SST might contribute zonally elongated precipitation.

Fig. 1 Weather chart at 9 a.m. on June 30th, 2018

JMA

Fig. 6 Phase diagram of BSISO mode

Kikuchi. (2012)

PC1

PC2

Phase 7

Phase 8

Phase 6

Phase 4

Phase 3

Phase 1

Phase 5

Phase 2

Hypothesis

Precipitation variability associated with the BSISO would be different upon

SST condition near East Asia

Fig. 10 The phase diagram of BSISO PCs (blue) time series for JJASO

during 2000-2019. The life cycle of BSISO events (black) from June

1st to July 23th in 2004. The number of BSISO events is given

PC2

Phase 7

(245)

Phase 8

(216)

Phase 6

(228)

Phase 4

(239)

Phase 3

(251)

Phase 1

(246)

Bay of Bengal

Ind

ia

& M

ari

tim

e C

on

tin

en

t

Western North Pacific

Ea

ste

rn N

ort

h P

ac

ific

&

eq

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ria

l In

dia

n O

ce

an

Phase 5

(240)

Phase 2

(225)

m /s

Snap shots (Fig. 11) indicate life cycle of the BSISO, which means propagation of the

active convection (blue Color) in Asian region.

Two main characteristics of precipitation among BSISO phases (Fig. 13)▪ Significant positive precipitation anomaly in eastern China during BSISO phase 3, 5▪ Significant positive precipitation anomaly over western North Pacific in BSISO phase 2, 7, 8

Fig. 2 25-90-day filtered OLR (Color) & UV850 (vector) anomalies averaged from June 28th to July 8th in 2018. Blue Color indicates convection

m /s

W /m2

Heavy precipitation over western Japan from June 28th to July 8th in 2018 cause severe damage to human society (Fig. 1).

25-90-day active convection and southerly wind anomaly were noticeable in the period of heavy precipitation (Fig. 2).



Two main characteristics of synoptic circulation among BSISO phases (Fig. 12)▪ Anti-cyclonic circulation in western North Pacific in BSISO phase 3, 4, 6▪ Cyclonic circulation in western North Pacific during BSISO phase 2, 7, 8

Cyclonic circulation

in WNP Anti-cyclonic circulation

in WNP

Anti-cyclonic circulation

in WNP

Anti-cyclonic circulation

in WNP Cyclonic circulation in WNP Cyclonic circulation in WNP

Positive rainfall

anomaly in China

Positive rainfall

anomaly in WNP

Positive rainfall

anomaly in WNP

Positive rainfall

anomaly in WNP

Positive rainfall

anomaly in China

Zonally elongated precipitation

25-90-day bandpass filter on

OLR, UV850, precipitation

to examine the effect of BSISO

minus

SST anomaly

> + 0.5SST anomaly

< - 0.5minus

Background

W /m2

m /s

m /s

m /s

m /s

Documents

Effect of sea surface temperature on precipitation