Roles of convective heating and boundary-layer moisture asymmetry in slowing down the convectively coupled Kelvin waves

Wang, Lu; Li, Tim

doi:10.1007/s00382-016-3215-3

Cited by 11 publications

(5 citation statements)

References 68 publications

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“…Furthermore, Wang and Li (1994) hypothesized the frictionally coupled Kelvin-Rossby wave theory, which includes the frictional convective coupled Kelvin-Rossby wave and evaporation-wind feedback process. Through the analyses of the column integrated Moisture Energy (MSE), previous works (Sobel et al 2014;Wang and Li 2017) reached a new understanding from the perspective of moisture mode. The above studies thus provide us with dynamic or moisture views to study the ISO propagation.…”

Section: Observed Iso Propagation Differencesmentioning

confidence: 99%

Cumulative positive contributions of propagating ISO to the quick low-level atmospheric response during El Niño developing years

Wang

Liu

et al. 2021

Clim Dyn

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Based on the Australian Bureau of Meteorology (BoM) El Niño alert system, this study investigates the atmospheric and oceanic conditions during El Niño developing years between 1982 and 2016. It is found that there is a 2-5-month (subseasonal-to-seasonal) lag to establish the steady low-level atmospheric (or the Southern Oscillation Index, SOI) response than the steady El Niño-pattern Sea Surface Temperature Anomaly (SSTA), which is defined as the critical period in this research. According to the duration of this critical period, the quick and slow steady atmospheric response years can be identified among all El Niño-Southern Oscillation (ENSO) developing events. The quick establishments of the Sea Level Pressure Anomaly (SLPA) in the tropical atmosphere are proved to be closely related to the tropical atmospheric Intra-seasonal Oscillation (ISO) events. In the quick response years, the ISO events can even propagate to the eastern tropical Pacific, which lead to the cumulative negative Outgoing Longwave Radiation (OLR) and SLP anomalies there, and make a positive contribution to the quick atmospheric response at the end of the critical period. However, the eastward-propagation of ISO events is mainly restricted in the tropical Western Pacific in the slow response years, causing slow steady atmospheric response with almost no contributions from ISO. Furthermore, observations and several simulations are used to understand this propagation differences of the ISO between quick and slow response years.

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Section: Observed Iso Propagation Differencesmentioning

confidence: 99%

Cumulative positive contributions of propagating ISO to the quick low-level atmospheric response during El Niño developing years

Wang

Liu

et al. 2021

Clim Dyn

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“…The negative OLR and T b anomalies are often used as a proxy to identify and detect tropical convection (e.g., Raghavendra et al 2018). While the OLR dataset has been used in numerous studies to understand convection and dynamics in the tropics (e.g., WK99; Roundy 2018), only few papers have performed similar analyses using T b data (e.g., Wang and Chen 2016;Wang and Li 2017).…”

Section: Fig 1 Global Tropical Convection (158n-158smentioning

confidence: 99%

Trends in Tropical Wave Activity from the 1980s to 2016

2019

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A frequency–wavenumber power () spectrum was constructed using satellite-derived outgoing longwave radiation (OLR) and brightness temperature for the tropical latitudes. Since the two datasets overlap for over 34 years with nonintersecting sources in error and compare relatively well with each other, it is possible to diagnose trends in the tropical wave activity from the two datasets with confidence. The results suggest a weakening trend in characterized by high interannual variability for wave activity occurring in the low-frequency part of the spectrum and a steady increase in with relatively low interannual variability for wave activity occurring in the high-frequency part of the spectrum. The results show the parts of the spectrum representing the Madden–Julian oscillation and equatorial Rossby wave losing and other parts of the spectrum representing Kelvin waves, mixed Rossby–gravity waves, and tropical disturbance–like wave activity gaining . Similar results were obtained when trends in variance corresponding to the first principal component were produced using spectrally filtered OLR data representative of atmospheric equatorial waves. Spatial trends in the active phase of wave events and the mean duration of events are also shown for the different wave types. Linear trends in for the entire spectrum and regional means in the spectrum corresponding to the abovementioned five wave types with confidence intervals are also presented in the paper. Finally, we demonstrate that El Niño–Southern Oscillation variability does not appear to control the overall spatial patterns and trends observed in the spectrum.

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“…Nevertheless, the close relationship between OLR and 150-hPa ∇ 𝑥 𝑧 ′ still holds in ERA-20C data with their correlation coefficients ranging between -0.7 and -0.9 over the MJO-active region (statistically significant at the 99.9% confidence level), implying that the ERA-20C 150-hPa ∇ 𝑥 𝑧 ′ could well reflect MJO's convection feature and it is reasonable to derive OLR anomaly from ERA-20C products. The statistical significance of correlation coefficients here and throughout the paper is tested using Student's t-test, with the degree of freedom estimated following Wang and Li (2017) considering the reduction of degree of freedom due to filtering. 3a).…”

Section: -Hpamentioning

confidence: 99%

Geopotential-based Multivariate MJO Index: extending RMM-like indices to pre-satellite era

et al. 2022

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Model simulations suggest that Madden-Julian Oscillation (MJO) activity changes under the anthropogenic climate change background. However, satellite observations, which provide information of MJO convection activity, are not available before the 1970s, hindering research on the historical longterm variability of MJO. This study aims at extending the data length of MJO indices that include both MJO circulation and convection features, such as the widely used Real-Multivariate MJO (RMM) index, to the pre-satellite era. This paper introduces a new MJO index construction method, of which the outgoing longwave radiation (OLR) input is derived from upper-level geopotential, and names it as the Geopotential-based Multivariate MJO (GMM) index. The GMM index is derived over 1902-2008 and compared with the filtered version of RMM (FMM) index during 1981-2008. The GMM index is shown to (1) have the same climatological properties as the FMM index, (2) be statistically highly correlated to the FMM index, and (3) be able to indicate MJO activities and its convection features in the pre-satellite era. The overall bivariate correlation between FMM index and GMM index based on ERA-20C ranges from 0.959 to 0.968 in different phases. Evaluation results confirm the validity of the proposed MJO index construction method, which could capture MJO convection activity in the pre-satellite era and can be applied to all MJO indices that require input of OLR. This study provides an alternative way that overcomes the difficulty of historical MJO studies, and will be beneficial to our understanding of the long-term change of MJO.

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Roles of convective heating and boundary-layer moisture asymmetry in slowing down the convectively coupled Kelvin waves

Cited by 11 publications

References 68 publications

Cumulative positive contributions of propagating ISO to the quick low-level atmospheric response during El Niño developing years

Cumulative positive contributions of propagating ISO to the quick low-level atmospheric response during El Niño developing years

Trends in Tropical Wave Activity from the 1980s to 2016

Geopotential-based Multivariate MJO Index: extending RMM-like indices to pre-satellite era

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