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  • DYNAMO/CINDY/AMIE/LASP: Processes, Dynamics, and Prediction of MJO Initiation x
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Richard H. Johnson and Paul E. Ciesielski

1. Introduction A major challenge in numerical weather and climate prediction is the realistic treatment of the atmospheric boundary layer (ABL) ( Teixeira et al. 2008 ). Complicating factors include the coupling of the boundary layer with the underlying surface, stratification effects, surface inhomogeneities, complex turbulent structures, intermittency, and nonlocal mixing. An additional difficulty, particularly in the tropics, is the coupling of the ABL with the cloud layer, including

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Brandon W. Kerns and Shuyi S. Chen

1. Introduction The Madden–Julian oscillation (MJO) is the dominant intraseasonal (20–90 day) mode of variability in the tropics ( Madden and Julian 1971 , 1972 , 1994 ; Zhang 2005 ). It is most active during boreal winter. Convectively active phases of the MJO are characterized by rainy periods that can last several weeks at a given location. In the Indian Ocean, the MJO can be described as a packet or envelope of convection centered near the equator moving eastward at ~5–10 m s −1 . The

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Nick Guy and David P. Jorgensen

a common MCS definition of contiguous precipitating convective clouds with a minimum length scale of at least 100 km. There is a great deal of literature describing the morphology and characteristics of MCSs, which account for a large amount of precipitation in the tropics and interact with the larger environment. Various modes of structural organization exist (e.g., Houze et al. 1990 )—from highly organized systems that exhibit linearly aligned convective cell elements, often with an

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George N. Kiladis, Juliana Dias, Katherine H. Straub, Matthew C. Wheeler, Stefan N. Tulich, Kazuyoshi Kikuchi, Klaus M. Weickmann, and Michael J. Ventrice

13 , the fact that the RMM amplitude may at times be weak even with the presence of an “MJO like” convective signal, or strong in the absence of such a signal, raises the question of which fundamental characteristics of the MJO should be used to define it. While we will not directly address this issue here, we point out that the essential circulation features of MJO teleconnections in both the tropics and extratropics can be reproduced in a dry primitive equation model by forcing associated with

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Simon P. de Szoeke, Eric D. Skyllingstad, Paquita Zuidema, and Arunchandra S. Chandra

Abstract

Cold pools dominate the surface temperature variability observed over the central Indian Ocean (0°, 80°E) for 2 months of research cruise observations in the Dynamics of the Madden–Julian Oscillation (DYNAMO) experiment in October–December 2011. Cold pool fronts are identified by a rapid drop of temperature. Air in cold pools is slightly drier than the boundary layer (BL). Consistent with previous studies, cold pools attain wet-bulb potential temperatures representative of saturated downdrafts originating from the lower midtroposphere.

Wind and surface fluxes increase, and rain is most likely within the ~20-min cold pool front. Greatest integrated water vapor and liquid follow the front. Temperature and velocity fluctuations shorter than 6 min achieve 90% of the surface latent and sensible heat flux in cold pools. The temperature of the cold pools recovers in about 20 min, chiefly by mixing at the top of the shallow cold wake layer, rather than by surface flux.

Analysis of conserved variables shows mean BL air is composed of 51% air entrained from the BL top (800 m), 22% saturated downdrafts, and 27% air at equilibrium with the ocean surface. The number of cold pools, and their contribution to the BL heat and moisture, nearly doubles in the convectively active phase compared to the suppressed phase of the Madden–Julian oscillation.

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Eric D. Skyllingstad and Simon P. de Szoeke

( Rotunno et al. 1988 ; Weckwerth and Parsons 2006 ; Houston and Wilhelmson 2012 ). In the deep tropics, cold pools can cause a more than doubling of the local latent heat flux ( Jabouille et al. 1996 ). Understanding how cold pools interact and potentially enhance tropical convection is important for accurate representation of convection in large-scale models where these processes are not well resolved. On average, heating by deep convection through condensation is the primary mechanism that balances

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Michael S. Pritchard and Christopher S. Bretherton

aquaplanet can result in systematic MJO speedup ( Anderson 2012 ). This paper expands on the investigation of whether a clean causal link between MJO phase speed and moisture advection can be demonstrated in a global model with a realistic MJO. This is achieved by analyzing the sensitivity of the superparameterized MJO to surgically interfering with horizontal moisture advection by vorticity anomalies in the tropics. Two novel elements of our experiment design compared to the above work are 1) that it

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Weixin Xu and Steven A. Rutledge

1. Introduction The Madden–Julian oscillation (MJO) ( Madden and Julian 1971 , 1972 ) is the most remarkable intraseasonal concept in the tropics. The MJO has broad impacts on the global weather and climate ( Lau and Waliser 2005 ; Zhang 2005 , 2013 ) such as monsoon onset and rainfall variability ( Lau and Chan 1986 ; Hendon and Liebmann 1990 ; Lawrence and Webster 2002 ), tropical cyclone frequency ( Liebmann et al. 1994 ; Maloney and Hartmann 2000 ), tornado outbreaks ( Thompson and

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Douglas C. Stolz, Steven A. Rutledge, Weixin Xu, and Jeffrey R. Pierce

anomalies in the large-scale circulation associated with the MJO have been shown to circumnavigate the global tropics ( Madden and Julian 1994 ; Zhang 2005 ). Furthermore, the MJO has been implicated as a modulator of regional monsoon patterns, tropical cyclones, tornadoes, lightning, and extratropical weather/climate ( Zhang 2013 ). The Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign ( Yoneyama et al. 2013 ) took place during boreal fall and winter of 2011/12 in the central

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Tim Li, Chongbo Zhao, Pang-chi Hsu, and Tomoe Nasuno

1. Introduction The Madden–Julian oscillation [MJO; i.e., the intraseasonal oscillation (ISO)] is the most prominent mode of intraseasonal variability in the tropics. First identified by Madden and Julian (1971) using single station data from Canton Island (2.5°S, 171.4°W), the MJO is characterized by a wavenumber one structure with a thermal direct vertical cell propagating eastward along the equator ( Madden and Julian 1972 ). Later analysis of satellite data, such as outgoing longwave

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