MJO and CCEW modulation on South China Sea and Maritime Continent boreal winter subseasonal peak precipitation

Tsai, Wayne Yuan-Huai; Lu, Mong‐Ming; Sui, Chung‐Hsiung; Lin, Po‐Hsiung

doi:10.3319/tao.2019.10.28.01

Cited by 3 publications

(5 citation statements)

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“…In their study, one of the factors leading to the increase in the probability of extreme rainfall events is the high-amplitude n = 1 Rossby (R1) wave activity that intensifies the rainfall. Similarly, Tsai et al (2020) find that, during the winter monsoon period, the equatorial Rossby (ER) waves show strong positive modulation on peak rainfall intensity in the SCS-MC region. In another study, the convectively coupled ER waves double the chance of floods and increase the probability of extreme rainfall by 15-45% (Latos et al, 2021;Lubis and Respati, 2021).…”

Section: Introductionmentioning

confidence: 83%

“…Similarly, Tsai et al . (2020) find that, during the winter monsoon period, the equatorial Rossby (ER) waves show strong positive modulation on peak rainfall intensity in the SCS–MC region. In another study, the convectively coupled ER waves double the chance of floods and increase the probability of extreme rainfall by 15–45% (Latos et al ., 2021; Lubis and Respati, 2021).…”

Section: Introductionmentioning

confidence: 99%

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Equatorial Rossby waves on cold surge days and their impact on rainfall

Diong¹,

Xavier

Woolnough

et al. 2023

Quart J Royal Meteoro Soc

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This study aims to understand the process that determines the regional rainfall distribution in the equatorial South China Sea (SCS) and its surrounding during the cold surge (CS) days by looking at the different vorticity phases of active equatorial Rossby (R1) waves and the dynamics of the CSs related to the R1 wave. The CS can be thought of as an anticyclonic outflow from midlatitude and behaves like a dispersive group of R1 meridional modes. From the study, it shows the vorticity of the R1 wave arranges itself in such a way that the anticyclonic phase is located to the west and the cyclonic phase is located to the east of the cold CS axis. The CS winds in the equatorial SCS occur early, remain longer, and possess a larger zonal component in the active cyclonic phase compared with the active anticyclonic phase. During the active cyclonic vorticity phase, the rainfall anomalies pattern in the equatorial SCS changes from a “tick‐mark‐like” pattern to a “V‐shape” pattern as a consequence of the westward propagation of the wave. The probability of rainfall increases near the centre of cyclonic vorticity, but for anticyclonic vorticity the probability increases in the southern part of the vorticity centre. There is both increased (decreased) intensity and probability of extreme rainfall events during the active cyclonic (anticyclonic) vorticity phase on CS days. Overall, the rainfall anomalies are largely dominated by changes in the intensity on wet days rather than the number of wet days. These changes indicate the roles of the R1 wave vorticity phase in the rainfall distribution during CS days. The timing of enhancement and suppression of rain will provide additional valuable information to help improve forecast extreme weather events.

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Section: Introductionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Equatorial Rossby waves on cold surge days and their impact on rainfall

Diong¹,

Xavier

Woolnough

et al. 2023

Quart J Royal Meteoro Soc

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“…The wavenumber-frequency ranges are based on Wheeler and Kiladis [23]. The convection modulation of MJO and individual CCEWs is identified based on the same procedure described in Tsai et al [17]. We use the rank order of the wave-filtered OLR to flag the dates of the study period as a day of the "convective", "no signal", and "suppressed" phases.…”

Section: Identifying Mjo and Ccewsmentioning

confidence: 99%

“…The convective status of each wave is determined according to the threshold values of the wave-filtered OLR. The threshold values are defined by the first (Q 25 ) and third (Q 75 ) quartiles of the filtered daily OLR anomalies collected during the boreal winter half year (November-April) from 1998 to 2015 of all grid points in a large domain bounded by the longitudes of 105 • E and 135 • E and latitudes of 15 • S and 15 • N. The thresholds for each type of wave are summarized in Table 1 of Tsai et al [17]. When the filtered OLR anomaly is lower than Q 25 and the raw OLR value is less than 250 W m −2 , the day is flagged as the convective phase, while if it is higher than Q 75 , the day is flagged as the suppressed phase, otherwise the day is flagged as no signal.…”

Section: Identifying Mjo and Ccewsmentioning

confidence: 99%

“…They defined the extreme rainfall as the monthly maximum consecutive 5-day precipitation totals. On the other hand, in order to evaluate the usefulness of subseasonal to seasonal (S2S) prediction [16], Tsai et al [17] defined a subseasonal peak rainfall event Table 1. The detailed information about the three S2S models (updated from Vitart et al [19] according to ECMWF website), where "Time Range" is the forecast lead time, "Ensemble Size" is the number of members in the real-time forecast ensemble, and "Frequency" is the frequency the model is run.…”

Section: Introductionmentioning

confidence: 99%

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Subseasonal Forecasts of the Northern Queensland Floods of February 2019: Causes and Forecast Evaluation

Tsai

Sui

et al. 2021

Atmosphere

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During the austral summer 2018/19, devastating floods occurred over northeast Australia that killed approximately 625,000 head of cattle and inundated over 3000 homes in Townsville. In this paper, the disastrous event was identified as a record-breaking subseasonal peak rainfall event (SPRE). The SPRE was mainly induced by an anomalously strong monsoon depression that was modulated by the convective phases of an MJO and an equatorial Rossby (ER) wave. The ER wave originated from an active equatorial deep convection associated with the El Niño warm sea surface temperatures near the dateline over the central Pacific. Based on the S2S Project Database, we analyzed the extended-range forecast skill of the SPRE from two different perspectives, the monsoon depression represented by an 850-hPa wind shear index and the 15-day accumulated precipitation characterized by the percentile rank (PR) and the ratio to the three-month seasonal (DJF) totals. The results of four S2S models of this study suggest that the monsoon depression can maintain the same level of skill as the short-range (3 days) forecast up to 8–10 days. For precipitation parameters, the conclusions are similar to the monsoon depression. For the 2019 northern Queensland SPRE, the model forecast was, in general, worse than the expectation derived from the hindcast analysis. The clear modulation of the ER wave that enhanced the SPRE monsoon depression circulation and precipitation is suspected as the main cause for the lower forecast skill. The analysis procedure proposed in this study can be applied to analyze the SPREs and their associated large-scale drivers in other regions.

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The Philippine springtime (February–April) sub-seasonal rainfall extremes and extended-range forecast skill assessment using the S2S database

Tsai

Huang

et al. 2023

Weather and Climate Extremes

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MJO and CCEW modulation on South China Sea and Maritime Continent boreal winter subseasonal peak precipitation

Cited by 3 publications

References 0 publications

Equatorial Rossby waves on cold surge days and their impact on rainfall

Equatorial Rossby waves on cold surge days and their impact on rainfall

Subseasonal Forecasts of the Northern Queensland Floods of February 2019: Causes and Forecast Evaluation

The Philippine springtime (February–April) sub-seasonal rainfall extremes and extended-range forecast skill assessment using the S2S database

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