scholarly journals Modeling Diurnal and Intraseasonal Variability of the Ocean Mixed Layer

2005 ◽  
Vol 18 (8) ◽  
pp. 1190-1202 ◽  
Author(s):  
D. J. Bernie ◽  
S. J. Woolnough ◽  
J. M. Slingo ◽  
E. Guilyardi
Keyword(s):  
Mixed Layer ◽  
Diurnal Cycle ◽  
Intraseasonal Variability ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
Ocean Mixed Layer ◽  
Tropical Ocean ◽  
Toga Coare ◽  
The Impact ◽  
The Western Pacific

Abstract The intraseasonal variability of SST associated with the passage of the Madden–Julian oscillation (MJO) is well documented; yet coupled model integrations generally underpredict the magnitude of this SST variability. Observations from the Improved Meteorological Instrument (IMET) mooring in the western Pacific during the intensive observing period (IOP) of the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) showed a large diurnal signal in SST that is modulated by the passage of the MJO. In this study, observations from the IOP of the TOGA COARE and a one-dimensional (1D) ocean mixed layer model incorporating the K-Profile Parameterization (KPP) vertical mixing scheme have been used to investigate the rectification of the intraseasonal variability of SST by the diurnal cycle and the implied impact of the absence of a representation of this process on the modeled intraseasonal variability in coupled GCMs. Analysis of the SST observations has shown that the increase of the daily mean SST by the diurnal cycle of SST accounts for about one-third of the magnitude of intraseasonal variability of SST associated with the Madden–Julian oscillation in the western Pacific warm pool. Experiments from the 1D model forced with fluxes at a range of temporal resolutions and with differing vertical resolution of the model have shown that to capture 90% of the diurnal variability of SST, and hence 95% of the intraseasonal variability of SST, requires a 3-h or better temporal resolution of the fluxes and a vertical grid with an upper-layer thickness of the order of 1 m. In addition to the impact of the representation of the diurnal cycle on the intraseasonal variability of SST, the strength of the mixing across the thermocline was found to be enhanced by the proper representation of the nighttime deep mixing in the ocean, implying a possible impact of the diurnal cycle onto the mean climate of the tropical ocean.

scholarly journals The Madden–Julian Oscillation and Boreal Winter Forecast Skill: An Analysis of NCEP CFSv2 Reforecasts

2015 ◽  
Vol 28 (15) ◽  
pp. 6297-6307 ◽  
Author(s):  
Charles Jones ◽  
Abheera Hazra ◽  
Leila M. V. Carvalho
Keyword(s):  
Forecast Skill ◽  
Western Pacific ◽  
Boreal Winter ◽  
Lead Times ◽  
Madden Julian Oscillation ◽  
Main Mode ◽  
Weather Forecasts ◽  
Synoptic Variability ◽  
The Impact ◽  
The Western Pacific

Abstract The Madden–Julian oscillation (MJO) is the main mode of tropical intraseasonal variations and bridges weather and climate. Because the MJO has a slow eastward propagation and longer time scale relative to synoptic variability, significant interest exists in exploring the predictability of the MJO and its influence on extended-range weather forecasts (i.e., 2–4-week lead times). This study investigates the impact of the MJO on the forecast skill in Northern Hemisphere extratropics during boreal winter. Several 45-day forecasts of geopotential height (500 hPa) from NCEP Climate Forecast System version 2 (CFSv2) reforecasts are used (1 November–31 March 1999–2010). The variability of the MJO expressed as different amplitudes, durations, and recurrence (i.e., primary and successive events) and their influence on forecast skill is analyzed and compared against inactive periods (i.e., null cases). In general, forecast skill during enhanced MJO convection over the western Pacific is systematically higher than in inactive days. When the enhanced MJO convection is over the Maritime Continent, forecasts are lower than in null cases, suggesting potential model deficiencies in accurately forecasting the eastward propagation of the MJO over that region and the associated extratropical response. In contrast, forecasts are more skillful than null cases when the enhanced convection is over the western Pacific and during long, intense, and successive MJO events. These results underscore the importance of the MJO as a potential source of predictability on 2–4-week lead times.

scholarly journals Impact of the Madden–Julian Oscillation on Summer Rainfall in Southeast China

2009 ◽  
Vol 22 (2) ◽  
pp. 201-216 ◽  
Author(s):  
Lina Zhang ◽  
Bizheng Wang ◽  
Qingcun Zeng
Keyword(s):  
Indian Ocean ◽  
Tropical Indian Ocean ◽  
Summer Rainfall ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
Energy Propagation ◽  
Southeast China ◽  
The Indian Ocean ◽  
The Impact ◽  
The Western Pacific

Abstract The impact of the Madden–Julian oscillation (MJO) on summer rainfall in Southeast China is investigated using the Real-time Multivariate MJO (RMM) index and the observational rainfall data. A marked transition of rainfall patterns from being enhanced to being suppressed is found in Southeast China (east of 105°E and south of 35°N) on intraseasonal time scales as the MJO convective center moves from the Indian Ocean to the western Pacific Ocean. The maximum positive and negative anomalies of regional mean rainfall are in excess of 10% relative to the climatological regional mean. Such different rainfall regimes are associated with the corresponding changes in physical fields such as the western Pacific subtropical high (WPSH), moisture, and vertical motions. When the MJO is mainly over the Indian Ocean, the WPSH shifts farther westward, and the moisture and upward motions in Southeast China are increased. In contrast, when the MJO enters the western Pacific, the WPSH retreats eastward, and the moisture and upward motions in Southeast China are decreased. It is suggested that the MJO may influence summer rainfall in Southeast China through remote and local dynamical mechanisms, which correspond to the rainfall enhancement and suppression, respectively. The remote role is the energy propagation of the Rossby wave forced by the MJO-related heating over the Indian Ocean through the low-level westerly waveguide from the tropical Indian Ocean to Southeast China. The local role is the northward shift of the upward branch of the anomalous meridional circulation when the MJO is over the western Pacific, which causes eastward retreat of the WPSH and suppressed moisture transport toward Southeast China.

Symmetric and Antisymmetric Convection Signals in the Madden–Julian Oscillation. Part I: Basic Modes in Infrared Brightness Temperature

2014 ◽  
Vol 71 (9) ◽  
pp. 3302-3326 ◽  
Author(s):  
Wen-wen Tung ◽  
Dimitrios Giannakis ◽  
Andrew J. Majda
Keyword(s):  
Brightness Temperature ◽  
Diurnal Cycle ◽  
Propagation Speed ◽  
Boreal Winter ◽  
Single Pair ◽  
Madden Julian Oscillation ◽  
Tropical Ocean ◽  
Symmetric Component ◽  
Toga Coare ◽  
Infrared Brightness

Abstract This work studies the significance of north–south asymmetry in convection associated with the 20–90-day Madden–Julian oscillation (MJO) propagating across the equatorial Indo-Pacific warm pool region. Satellite infrared brightness temperature data in the tropical belt for the period 1983–2006 were decomposed into components symmetric and antisymmetric about the equator. Using a recent nonlinear objective method called nonlinear Laplacian spectral analysis, modes of variability were extracted representing symmetric and antisymmetric features of MJO convection signals, along with a plethora of other modes of tropical convective variability spanning diurnal to interannual time scales. The space–time reconstruction of these modes during the 1992/93 Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) period is described in detail. In particular, the boreal winter MJO emerges as a single pair of modes in both symmetric and antisymmetric convection signals. Both signals originate in the Indian Ocean around 60°E. They coexist for all significant MJO events with a varying degree of relative importance, which is affected by ENSO. The symmetric signals tend to be suppressed when crossing the Maritime Continent, while the antisymmetric signals are not as inhibited. Their differences in peak phase and propagation speed suggest fundamental differences in the underlying mechanisms. The multiscale interactions between the diurnal, MJO, and ENSO modes of convection were studied. It was found that the symmetric component of MJO convection appears out of phase with the symmetric component of the diurnal cycle, while the antisymmetric component of MJO convection is in phase with the antisymmetric diurnal cycle. The former relationship likely breaks down during strong El Niño events, and both relationships likely break down during prolonged La Niña events.

scholarly journals The Effect of Atmosphere–Ocean Coupling on the Structure and Intensity of Tropical Cyclone Bejisa in the Southwest Indian Ocean

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 688
Author(s):  
Soline Bielli ◽  
Christelle Barthe ◽  
Olivier Bousquet ◽  
Pierre Tulet ◽  
Joris Pianezze
Keyword(s):  
Tropical Cyclone ◽  
Mixed Layer ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Ocean Mixed Layer ◽  
Surface Cooling ◽  
Southwest Indian Ocean ◽  
Left Hand ◽  
Sea Surface Cooling ◽  
The Impact

A set of numerical simulations is relied upon to evaluate the impact of air-sea interactions on the behaviour of tropical cyclone (TC) Bejisa (2014), using various configurations of the coupled ocean-atmosphere numerical system Meso-NH-NEMO. Uncoupled (SST constant) as well as 1D (use of a 1D ocean mixed layer) and 3D (full 3D ocean) coupled experiments are conducted to evaluate the impact of the oceanic response and dynamic processes, with emphasis on the simulated structure and intensity of TC Bejisa. Although the three experiments are shown to properly capture the track of the tropical cyclone, the intensity and the spatial distribution of the sea surface cooling show strong differences from one coupled experiment to another. In the 1D experiment, sea surface cooling (∼1 ∘C) is reduced by a factor 2 with respect to observations and appears restricted to the depth of the ocean mixed layer. Cooling is maximized along the right-hand side of the TC track, in apparent disagreement with satellite-derived sea surface temperature observations. In the 3D experiment, surface cooling of up to 2.5 ∘C is simulated along the left hand side of the TC track, which shows more consistency with observations both in terms of intensity and spatial structure. In-depth cooling is also shown to extend to a much deeper depth, with a secondary maximum of nearly 1.5 ∘C simulated near 250 m. With respect to the uncoupled experiment, heat fluxes are reduced from about 20% in both 1D and 3D coupling configurations. The tropical cyclone intensity in terms of occurrence of 10-m TC wind is globally reduced in both cases by about 10%. 3D-coupling tends to asymmetrize winds aloft with little impact on intensity but rather a modification of the secondary circulation, resulting in a slight change in structure.

scholarly journals Seasonality and Dynamics of Atmospheric Teleconnection from the Tropical Indian Ocean and the Western Pacific to West Antarctica

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 849
Author(s):  
Hyun-Ju Lee ◽  
Emilia-Kyung Jin
Keyword(s):  
Indian Ocean ◽  
Rossby Wave ◽  
Tropical Indian Ocean ◽  
Western Pacific ◽  
Tropical Region ◽  
Formation Mechanisms ◽  
West Antarctica ◽  
Background Flow ◽  
The Impact ◽  
The Western Pacific

The global impact of the tropical Indian Ocean and the Western Pacific (IOWP) is expected to increase in the future because this area has been continuously warming due to global warming; however, the impact of the IOWP forcing on West Antarctica has not been clearly revealed. Recently, ice loss in West Antarctica has been accelerated due to the basal melting of ice shelves. This study examines the characteristics and formation mechanisms of the teleconnection between the IOWP and West Antarctica for each season using the Rossby wave theory. To explicitly understand the role of the background flow in the teleconnection process, we conduct linear baroclinic model (LBM) simulations in which the background flow is initialized differently depending on the season. During JJA/SON, the barotropic Rossby wave generated by the IOWP forcing propagates into the Southern Hemisphere through the climatological northerly wind and arrives in West Antarctica; meanwhile, during DJF/MAM, the wave can hardly penetrate the tropical region. This indicates that during the Austral winter and spring, the IOWP forcing and IOWP-region variabilities such as the Indian Ocean Dipole (IOD) and Indian Ocean Basin (IOB) modes should paid more attention to in order to investigate the ice change in West Antarctica.

scholarly journals Evolution of the Madden–Julian Oscillation in Two Types of El Niño

2016 ◽  
Vol 29 (5) ◽  
pp. 1919-1934 ◽  
Author(s):  
Xiong Chen ◽  
Jian Ling ◽  
Chongyin Li
Keyword(s):  
El Niño ◽  
El Nino ◽  
Moisture Flux ◽  
Early Summer ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
Central Pacific ◽  
Cp El Niño ◽  
Ep El Niño ◽  
The Western Pacific

Abstract Evolution characteristics of the Madden–Julian oscillation (MJO) during the eastern Pacific (EP) and central Pacific (CP) types of El Niño have been investigated. MJO activities are strengthened over the western Pacific during the predeveloping and developing phases of EP El Niño, but suppressed during the mature and decaying phases. In contrast, MJO activities do not show a clear relationship with CP El Niño before their occurrence over the western Pacific, but they increase over the central Pacific during the mature and decaying phases of CP El Niño. Lag correlation analyses further confirm that MJO activities over the western Pacific in boreal spring and early summer are closely related to EP El Niño up to 2–11 months later, but not for CP El Niño. EP El Niño tends to weaken the MJO and lead to a much shorter range of its eastward propagation. Anomalous descending motions over the Maritime Continent and western Pacific related to El Niño can suppress convection and moisture flux convergence there and weaken MJO activities over these regions during the mature phase of both types of El Niño. MJO activities over the western Pacific are much weaker in EP El Niño due to the stronger anomalous descending motions. Furthermore, the MJO propagates more continuously and farther eastward during CP El Niño because of robust moisture convergence over the central Pacific, which provides adequate moisture for the development of MJO convection.

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