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  • 1. Jiang, Xianan
    et al.
    Waliser, Duane E.
    Xavier, Prince K.
    Petch, Jon
    Klingaman, Nicholas P.
    Woolnough, Steven J.
    Guan, Bin
    Bellon, Gilles
    Crueger, Traute
    DeMott, Charlotte
    Hannay, Cecile
    Lin, Hai
    Hu, Wenting
    Kim, Daehyun
    Lappen, Cara-Lyn
    Lu, Mong-Ming
    Ma, Hsi-Yen
    Miyakawa, Tomoki
    Ridout, James A.
    Schubert, Siegfried D.
    Scinocca, John
    Seo, Kyong-Hwan
    Shindo, Eiki
    Song, Xiaoliang
    Stan, Cristiana
    Tseng, Wan-Ling
    Wang, Wanqiu
    Wu, Tongwen
    Wu, Xiaoqing
    Wyser, Klaus
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Zhang, Guang J.
    Zhu, Hongyan
    Vertical structure and physical processes of the Madden-Julian oscillation: Exploring key model physics in climate simulations2015Inngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 10, s. 4718-4748Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aimed at reducing deficiencies in representing the Madden-Julian oscillation (MJO) in general circulation models (GCMs), a global model evaluation project on vertical structure and physical processes of the MJO was coordinated. In this paper, results from the climate simulation component of this project are reported. It is shown that the MJO remains a great challenge in these latest generation GCMs. The systematic eastward propagation of the MJO is only well simulated in about one fourth of the total participating models. The observed vertical westward tilt with altitude of the MJO is well simulated in good MJO models but not in the poor ones. Damped Kelvin wave responses to the east of convection in the lower troposphere could be responsible for the missing MJO preconditioning process in these poor MJO models. Several process-oriented diagnostics were conducted to discriminate key processes for realistic MJO simulations. While large-scale rainfall partition and low-level mean zonal winds over the Indo-Pacific in a model are not found to be closely associated with its MJO skill, two metrics, including the low-level relative humidity difference between high- and low-rain events and seasonal mean gross moist stability, exhibit statistically significant correlations with the MJO performance. It is further indicated that increased cloud-radiative feedback tends to be associated with reduced amplitude of intraseasonal variability, which is incompatible with the radiative instability theory previously proposed for the MJO. Results in this study confirm that inclusion of air-sea interaction can lead to significant improvement in simulating the MJO.

  • 2. Klingaman, Nicholas P.
    et al.
    Woolnough, Steven J.
    Jiang, Xianan
    Waliser, Duane
    Xavier, Prince K.
    Petch, Jon
    Caian, Mihaela
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Hannay, Cecile
    Kim, Daehyun
    Ma, Hsi-Yen
    Merryfield, William J.
    Miyakawa, Tomoki
    Pritchard, Mike
    Ridout, James A.
    Roehrig, Romain
    Shindo, Eiki
    Vitart, Frederic
    Wang, Hailan
    Cavanaugh, Nicholas R.
    Mapes, Brian E.
    Shelly, Ann
    Zhang, Guang J.
    Vertical structure and physical processes of the Madden-Julian oscillation: Linking hindcast fidelity to simulated diabatic heating and moistening2015Inngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 10, s. 4690-4717Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many theories for the Madden-Julian oscillation (MJO) focus on diabatic processes, particularly the evolution of vertical heating and moistening. Poor MJO performance in weather and climate models is often blamed on biases in these processes and their interactions with the large-scale circulation. We introduce one of the three components of a model evaluation project, which aims to connect MJO fidelity in models to their representations of several physical processes, focusing on diabatic heating and moistening. This component consists of 20day hindcasts, initialized daily during two MJO events in winter 2009-2010. The 13 models exhibit a range of skill: several have accurate forecasts to 20days lead, while others perform similarly to statistical models (8-11days). Models that maintain the observed MJO amplitude accurately predict propagation, but not vice versa. We find no link between hindcast fidelity and the precipitation-moisture relationship, in contrast to other recent studies. There is also no relationship between models' performance and the evolution of their diabatic heating profiles with rain rate. A more robust association emerges between models' fidelity and net moistening: the highest-skill models show a clear transition from low-level moistening for light rainfall to midlevel moistening at moderate rainfall and upper level moistening for heavy rainfall. The midlevel moistening, arising from both dynamics and physics, may be most important. Accurately representing many processes may be necessary but not sufficient for capturing the MJO, which suggests that models fail to predict the MJO for a broad range of reasons and limits the possibility of finding a panacea.

  • 3. Xavier, Prince K.
    et al.
    Petch, Jon C.
    Klingaman, Nicholas P.
    Woolnough, Steve J.
    Jiang, Xianan
    Waliser, Duane E.
    Caian, Mihaela
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Cole, Jason
    Hagos, Samson M.
    Hannay, Cecile
    Kim, Daehyun
    Miyakawa, Tomoki
    Pritchard, Michael S.
    Roehrig, Romain
    Shindo, Eiki
    Vitart, Frederic
    Wang, Hailan
    Vertical structure and physical processes of the Madden-Julian Oscillation: Biases and uncertainties at short range2015Inngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 10, s. 4749-4763Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An analysis of diabatic heating and moistening processes from 12 to 36h lead time forecasts from 12 Global Circulation Models are presented as part of the Vertical structure and physical processes of the Madden-Julian Oscillation (MJO) project. A lead time of 12-36h is chosen to constrain the large-scale dynamics and thermodynamics to be close to observations while avoiding being too close to the initial spin-up of the models as they adjust to being driven from the Years of Tropical Convection (YOTC) analysis. A comparison of the vertical velocity and rainfall with the observations and YOTC analysis suggests that the phases of convection associated with the MJO are constrained in most models at this lead time although the rainfall in the suppressed phase is typically overestimated. Although the large-scale dynamics is reasonably constrained, moistening and heating profiles have large intermodel spread. In particular, there are large spreads in convective heating and moistening at midlevels during the transition to active convection. Radiative heating and cloud parameters have the largest relative spread across models at upper levels during the active phase. A detailed analysis of time step behavior shows that some models show strong intermittency in rainfall and differences in the precipitation and dynamics relationship between models. The wealth of model outputs archived during this project is a very valuable resource for model developers beyond the study of the MJO. In addition, the findings of this study can inform the design of process model experiments, and inform the priorities for field experiments and future observing systems.

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