Australia-Asian monsoon in two versions of the UK Met Office Unified Model and their impacts on tropical–extratropical teleconnections

Jin, Luxi; Zhang, H.; Moise, Aurel; Martin, Gill; Milton, Sean; Rodríguez, José M.

doi:10.1007/s00382-019-04821-1

Cited by 8 publications

(21 citation statements)

References 91 publications

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“…3, this bias is relatively small in the region along The model also shows strongly positive bias in overpredicting tropical rainfall in the Indian Ocean. This is a known problem in the UK Met Office (UKMO) Unified Model (Bush et al 2015;Levine and Martin 2018;Jin et al 2019); see Bush et al (2015) for analysis of this bias using Global Atmosphere 3.0 (GA3.0) models at N96 Fig. 3 DJF ACCESS-GPCP precipitation bias for hindcasts initialised on November 1.…”

Section: Simulation Of Spcz Rainfallmentioning

confidence: 99%

Scope for predicting seasonal variation of the SPCZ with ACCESS-S1

et al. 2021

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Regional seasonal forecasting requires accurate simulation of the variability of local climate drivers. The South Pacific Convergence Zone (SPCZ) is a large region of low-level convergence, clouds and precipitation in the South Pacific, whose effects extend as far as northeast Australia (NEA). The location of the SPCZ is modulated by the El Niño-Southern Oscillation (ENSO) which causes rainfall variability in the region. Correctly simulating the ENSO-SPCZ teleconnection and its interplay with local conditions is essential for improving seasonal rainfall forecasts. Here we analyse the ability of the ACCESS-S1 seasonal forecast system to predict the SPCZ’s relationship with ENSO including its latitudinal shifts, zonal slope and rainfall magnitude between 1990 and 2012 for the December–January–February (DJF) season. We found improvements in ACCESS-S1’s SPCZ prediction capability compared to its predecessor (POAMA), although prediction of the slope is still limited. The inability of ACCESS-S1 to replicate seasons with a strong anti-zonal SPCZ slope is attributed to its atmospheric model. This has implications for accurate seasonal rainfall forecasts for NEA and South Pacific Islands. Future challenges in seasonal prediction facing regional communities and developers of coupled ocean–atmosphere forecast models are discussed.

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Section: Simulation Of Spcz Rainfallmentioning

confidence: 99%

Scope for predicting seasonal variation of the SPCZ with ACCESS-S1

et al. 2021

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“…In this paper, we use monthly precipitation, winds, and geopotential height data obtained from numerical experiments with the UM GA6 and GA7 (Walters et al, 2017(Walters et al, , 2019) using a horizontal resolution of 60 km (N216 grid). We used atmosphere-only UM GA simulations by forcing the model with daily observed sea surface temperature (SST) and sea-ice conditions for the period 1982-2008, as in Walters et al (2017Walters et al ( , 2019 and Jin et al (2019).…”

Section: Modelmentioning

confidence: 99%

“…Part of the teleconnection patterns showed similarity with Rossby wave propagation from the tropics into the middle and high latitudes. However, as acknowledged by the authors, the underlying physical and dynamic processes supporting these improved rainfall teleconnection patterns and the increased ISMR in the simulations was not fully explored (Jin et al, 2019). The major goal of this study is therefore to further investigate how the simulation of Indian monsoon rainfall in GA6 and GA7 (Walters et al, 2017(Walters et al, , 2019 affects the representation of tropical-extratropical rainfall teleconnections, and the nature of the underlying physical and dynamical processes.…”

Section: Introductionmentioning

confidence: 97%

“…As noted in previous UM assessments (Walters et al, 2014(Walters et al, , 2017(Walters et al, , 2019, the UM has a climatological rainfall deficit over the Indian subcontinent. However, the simulation of Indian summer monsoon rainfall (ISMR) within a given UM configuration was shown to improve when the model resolution was increased (Prakash et al, 2016;Jin et al, 2019). In a recent UM GA assessment study, Jin et al (2019) showed that the area-averaged summer monsoon rainfall over the Indian subcontinent (70°-90°E, 5°-25°N) was significantly increased in GA7 compared with GA6.…”

Section: Introductionmentioning

confidence: 99%

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Representation of Rossby wave propagation and its effect on the teleconnection between the Indian summer monsoon and extratropical rainfall in the Met Office Unified Model

Tang

Zhang

et al. 2021

Preprint

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Compared with Global Atmosphere 6 (GA6) of the UK Met Office Unified Model (UM), the dry bias over the Indian monsoon region in Global Atmosphere 7 (GA7) is significantly reduced. However, the physical processes controlling how this reduced dry bias in India influences rainfall teleconnections in the extratropics remain unclear. Thus, in this study, we use Rossby wave tracing in a horizontally nonuniform background flow to investigate how the improved simulation of monsoon rainfall in GA7 compared with GA6 affects extratropical rainfall teleconnections. We find that wave rays emanating from the upper troposphere in the Indian monsoon region first propagate westward, then divide into the Northern Hemisphere (NH) subtropical westerlies over Asia and the Southern Hemisphere (SH) subtropical westerlies. The wave ray trajectories in GA7 in years of strong Indian summer monsoon rainfall (ISMR) are closer to observations than those in GA6. We also find that the upper tropospheric meridional winds over the South Asian monsoon region and western Tibetan Plateau are much better simulated in GA7 than in GA6 owning to the improvement of ISMR and South Asian High (SAH), which leads to a more realistic simulation of the wave rays in GA7. The better simulated circulation teleconnections in GA7 then modulate the vertical motion and moisture transport, and hence affect extratropical rainfall anomalies in the NH and SH. This paper provides new insights for the assessment of tropical–extratropical teleconnections in models.

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“…Moreover, the moisture flux convergence is enhanced over the Bay of Bengal, South China Sea, western North Pacific, and subtropical front zone in ECHAM_SMCM compared to ECHAM_CTRL. The intensification of

- \bar{〈\nabla ∙ \overset{false\to}{V} q〉}

over the Bay of Bengal may influence the precipitation over central Asia through the tropical‐extratropical teleconnection (e.g., Jin et al ., ). In addition, the enhanced

- \bar{〈\nabla ∙ \overset{false\to}{V} q〉}

over East Asia, including the western North Pacific, may impacts the simulation of East Asia summer monsoon.…”

Section: Possible Physical Processes Contributed To the Response Of Amentioning

confidence: 99%

Effects of a stochastic multicloud parameterization on the simulated Asian‐Australian monsoon rainfall in an AGCM

Jiang

Cao

2019

Intl Journal of Climatology

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The Asian‐Australian monsoon (AAM) plays a vital role in modulating the global and local climates. Current numerical models, including climate system models (CSMs) and atmospheric general circulation models (AGCMs), have difficulties in capturing the fundamental and intrinsic features of the AAM. By applying the stochastic multicloud model (SMCM) to the state‐of‐the‐art ECHAM6.3 atm model, we investigated the impacts of SMCM on the simulation of AAM precipitation. Though the modified model with the SMCM improves simulations of the AAM precipitation in June–July–August–September season, the solstice mode, the AAM domain, and the AAM precipitation intensity, deficiencies also exist in other aspects, that is, simulations of rainfall in December–January–February–March and April–May seasons, and the equinox mode. Analyses also unravelled the modified model improves in simulating the spatial patterns of seasonal variation of precipitation in the Indian monsoon region, western North Pacific monsoon region, and Australian monsoon region in terms of pattern correlation coefficient and normalized root‐mean square error scores. The enhanced simulation of solar radiation in the modified model favours improving the performance of the simulated solstice mode. In addition, moisture budget analysis was applied to investigate physical processes that modulate the variations and distributions of AAM precipitation. Analyses revealed that variations and distributions of the vertical integral of moisture flux convergence is closely associated with changes in precipitation, while the stratification of vertical moist transport is associated with changes in precipitation over land in the AAM region. In addition, the modified model influences the AAM precipitation mainly through the variations of moisture flux convergence. The present work potentially provides a method to improve the simulated capability of AGCMs.

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Australia-Asian monsoon in two versions of the UK Met Office Unified Model and their impacts on tropical–extratropical teleconnections

Cited by 8 publications

References 91 publications

Scope for predicting seasonal variation of the SPCZ with ACCESS-S1

Scope for predicting seasonal variation of the SPCZ with ACCESS-S1

Representation of Rossby wave propagation and its effect on the teleconnection between the Indian summer monsoon and extratropical rainfall in the Met Office Unified Model

Effects of a stochastic multicloud parameterization on the simulated Asian‐Australian monsoon rainfall in an AGCM

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