Embedding a One-column Ocean Model (SIT 1.06) in the Community Atmosphere Model 5.3 (CAM5.3; CAM5–SIT v1.0) to Improve Madden–Julian Oscillation Simulation in Boreal Winter

Abstract. The effect of the air–sea interaction on the Madden–Julian Oscillation (MJO) was investigated using the one-column ocean model Snow–Ice–Thermocline (SIT 1.06) embedded in the Community Atmosphere Model 5.3 (CAM5.3; hereafter CAM5–SIT v1.0). The SIT model with 41 vertical layers was developed to simulate sea surface temperature (SST) and upper-ocean temperature variations with a high vertical resolution that resolves the cool skin and diurnal warm layer and the upper oceanic mixed layer. A series of 30-year sensitivity experiments were conducted in which various model configurations (e.g., coupled versus uncoupled, vertical resolution and depth of the SIT model, coupling domains, and absence of the diurnal cycle) were considered to evaluate the effect of air–sea coupling on MJO simulation. Most of the CAM5–SIT experiments exhibited higher fidelity than the CAM5-alone experiment in characterizing the basic features of the MJO such as spatiotemporal variability and the eastward propagation in boreal winter. The overall MJO simulation performance of CAM5–SIT benefited from (1) better resolving the fine structure of upper-ocean temperature and therefore the air–sea interaction that resulted in more realistic intraseasonal variability in both SST and atmospheric circulation and (2) the adequate thickness and vertical resolution of the oceanic mixed layer. The sensitivity experiments demonstrated the necessity of coupling the tropical eastern Pacific in addition to the tropical Indian Ocean and the tropical western Pacific. Enhanced MJO could be obtained without considering the diurnal cycle in coupling.

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Modeling Diurnal and Intraseasonal Variability of the Ocean Mixed Layer

Journal of Climate ◽

10.1175/jcli3319.1 ◽

2005 ◽

Vol 18 (8) ◽

pp. 1190-1202 ◽

Cited By ~ 141

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.

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The Scale of Submesoscale Baroclinic Instability Globally

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0043.1 ◽

2020 ◽

Vol 50 (9) ◽

pp. 2649-2667 ◽

Cited By ~ 2

Author(s):

Jihai Dong ◽

Baylor Fox-Kemper ◽

Hong Zhang ◽

Changming Dong

Keyword(s):

Mixed Layer ◽

Spatial Scales ◽

Baroclinic Instability ◽

Ocean Model ◽

Median Surface ◽

Surface Mixed Layer ◽

Vertical Resolution ◽

High Vertical Resolution ◽

Mixed Layers ◽

Strong Seasonality

AbstractThe spatial scale of submesoscales is an important parameter for studies of submesoscale dynamics and multiscale interactions. The horizontal spatial scales of baroclinic, geostrophic-branch mixed layer instabilities (MLI) are investigated globally (without the equatorial or Arctic oceans) based on observations and simulations in the surface and bottom mixed layers away from significant topography. Three high-vertical-resolution boundary layer schemes driven with profiles from a MITgcm global submesoscale-permitting model improve robustness. The fastest-growing MLI wavelength decreases toward the poles. The zonal median surface MLI wavelength is 51–2.9 km when estimated from the observations and from 32, 25, and 27 km to 2.5, 1.2, and 1.1 km under the K-profile parameterization (KPP), Mellor–Yamada (MY), and κ–ε schemes, respectively. The surface MLI wavelength has a strong seasonality with a median value 1.6 times smaller in summer (10 km) than winter (16 km) globally from the observations. The median bottom MLI wavelengths estimated from simulations are 2.1, 1.4, and 0.41 km globally under the KPP, MY, and κ–ε schemes, respectively, with little seasonality. The estimated required ocean model grid spacings to resolve wintertime surface mixed layer eddies are 1.9 km (50% of regions resolved) and 0.92 km (90%) globally. To resolve summertime eddies or MLI seasonality requires grids finer than 1.3 km (50%) and 0.55 km (90%). To resolve bottom mixed layer eddies, grids finer than 257, 178, and 51 m (50%) and 107, 87, and 17 m (90%) are estimated under the KPP, MY, and κ–ε schemes.

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A Multiscale Model for the Intraseasonal Impact of the Diurnal Cycle over the Maritime Continent on the Madden–Julian Oscillation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0158.1 ◽

2016 ◽

Vol 73 (2) ◽

pp. 579-604 ◽

Cited By ~ 27

Author(s):

Andrew J. Majda ◽

Qiu Yang

Keyword(s):

Diurnal Cycle ◽

Numerical Models ◽

Multiscale Model ◽

Boreal Winter ◽

Madden Julian Oscillation ◽

Maritime Continent ◽

Upper Troposphere ◽

Planetary Scale ◽

Baroclinic Modes ◽

Huge Challenge

Abstract The eastward-propagating Madden–Julian oscillation (MJO) typically exhibits complex behavior during its passage over the Maritime Continent, sometimes slowly propagating eastward and other times stalling and even terminating there with large amounts of rainfall. This is a huge challenge for present-day numerical models to simulate. One possible reason is the inadequate treatment of the diurnal cycle and its scale interaction with the MJO. Here these two components are incorporated into a simple self-consistent multiscale model that includes one model for the intraseasonal impact of the diurnal cycle and another one for the planetary/intraseasonal circulation. The latter model is forced self-consistently by eddy flux divergences of momentum and temperature from a model for the diurnal cycle with two baroclinic modes, which capture the intraseasonal impact of the diurnal cycle. The MJO is modeled as the planetary-scale circulation response to a moving heat source on the synoptic and planetary scales. The results show that the intraseasonal impact of the diurnal cycle during boreal winter tends to strengthen the westerlies (easterlies) in the lower (upper) troposphere in agreement with the observations. In addition, the temperature anomaly induced by the intraseasonal impact of the diurnal cycle can cancel that from the symmetric–asymmetric MJO with convective momentum transfer, yielding stalled or suppressed propagation of the MJO across the Maritime Continent. The simple multiscale model should be useful for the MJO in observations or more complex numerical models.

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

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-13-0122.1 ◽

2014 ◽

Vol 71 (9) ◽

pp. 3302-3326 ◽

Cited By ~ 19

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.

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Impacts of Idealized Air–Sea Coupling on Madden–Julian Oscillation Structure in the Superparameterized CAM

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-04.1 ◽

2011 ◽

Vol 68 (9) ◽

pp. 1990-2008 ◽

Cited By ~ 38

Author(s):

James J. Benedict ◽

David A. Randall

Keyword(s):

Deep Convection ◽

Ocean Model ◽

Surface Fluxes ◽

Convective Heating ◽

Madden Julian Oscillation ◽

Kelvin Wave ◽

Coupled Simulation ◽

Wave Response ◽

Community Atmosphere Model ◽

Anomalous Surface

Abstract Air–sea interactions and their impact on intraseasonal convective organization are investigated by comparing two 5-yr simulations from the superparameterized Community Atmosphere Model version 3.0 (SP-CAM). The first is forced using prescribed sea surface temperatures (SSTs). The second is identical except that a simplified oceanic mixed-layer model is used to predict tropical SST anomalies that are coupled to the atmosphere. This partially coupled simulation allows SSTs to respond to anomalous surface fluxes. Implementation of the idealized slab ocean model in the SP-CAM results in significant changes to intraseasonal convective variability and organization. The more realistic treatment of air–sea interactions in the coupled simulation improves many aspects of tropical convection on intraseasonal scales, from the relationships between precipitation and SSTs to the space–time structure and propagation of the Madden–Julian oscillation (MJO). This improvement is associated with a more realistic convergence structure and longitudinal gradient of SST relative to MJO deep convection. In the uncoupled SP-CAM, SST is roughly in phase with the MJO convective center and the development of the Kelvin wave response and boundary layer convergence east of the convective center is relatively weak. In the coupled SP-CAM, maxima in SST lead maxima in MJO convection by cycle. Coupling produces warmer SSTs, a stronger Kelvin wave response, enhanced low-level convergence, and increased convective heating ahead (east) of the MJO convective center. Convective development east of the MJO precipitation center is more favorable in the coupled versus the uncoupled version, resulting in more realistic organization and clearer eastward propagation of the MJO in the coupled SP-CAM.

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On Air–Sea Interaction at the Mouth of the Gulf of California

Journal of Climate ◽

10.1175/jcli4089.1 ◽

2007 ◽

Vol 20 (9) ◽

pp. 1649-1661 ◽

Cited By ~ 12

Author(s):

Paquita Zuidema ◽

Chris Fairall ◽

Leslie M. Hartten ◽

Jeffrey E. Hare ◽

Daniel Wolfe

Keyword(s):

Boundary Layer ◽

Liquid Phase ◽

Mixed Layer ◽

Diurnal Cycle ◽

Gulf Of California ◽

Sea Breeze ◽

Near Surface ◽

Oceanic Mixed Layer ◽

The Mean ◽

Moist Layer

Abstract Surface flux, wind profiler, oceanic temperature and salinity, and atmospheric moisture, cloud, and wind observations gathered from the R/V Altair during the North American Monsoon Experiment (NAME) are presented. The vessel was positioned at the mouth of the Gulf of California halfway between La Paz and Mazatlan (∼23.5°N, 108°W), from 7 July to 11 August 2004, with a break from 22 to 27 July. Experiment-mean findings include a net heat input from the atmosphere into the ocean of 70 W m−2. The dominant cooling was an experiment-mean latent heat flux of 108 W m−2, equivalent to an evaporation rate of 0.16 mm h−1. Total accumulated rainfall amounted to 42 mm. The oceanic mixed layer had a depth of approximately 20 m and both warmed and freshened during the experiment, despite a dominance of evaporation over local precipitation. The mean atmospheric boundary layer depth was approximately 410 m, deepening with time from an initial value of 350 m. The mean near-surface relative humidity was 66%, increasing to 73% at the top of the boundary layer. The rawinsondes documented an additional moist layer between 2- and 3-km altitude associated with a land–sea breeze, and a broad moist layer at 5–6 km associated with land-based convective outflow. The observational period included a strong gulf surge around 13 July associated with the onset of the summer monsoon in southern Arizona. During this surge, mean 1000–700-hPa winds reached 12 m s−1, net surface fluxes approached zero, and the atmosphere moistened significantly but little rainfall occurred. The experiment-mean wind diurnal cycle was dominated by mainland Mexico and consisted of a near-surface westerly sea breeze along with two easterly return flows, one at 2–3 km and another at 5–6 km. Each of these altitudes experienced nighttime cloudiness. The corresponding modulation of the radiative cloud forcing diurnal cycle provided a slight positive feedback upon the sea surface temperature. Two findings were notable. One was an advective warming of over 1°C in the oceanic mixed layer temperature associated with the 13 July surge. The second was the high nighttime cloud cover fraction at 5–6 km, dissipating during the day. These clouds appeared to be thin, stratiform, slightly supercooled liquid-phase clouds. The preference for the liquid phase increases the likelihood that the clouds can be advected farther from their source and thereby contribute to a higher-altitude horizontal moisture flux into the United States.

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Surface Fluxes and Ocean Coupling in the Tropical Intraseasonal Oscillation

Journal of Climate ◽

10.1175/jcli-3212.1 ◽

2004 ◽

Vol 17 (22) ◽

pp. 4368-4386 ◽

Cited By ~ 142

Author(s):

Eric D. Maloney ◽

Adam H. Sobel

Keyword(s):

Mixed Layer ◽

Mixed Layer Depth ◽

Intraseasonal Variability ◽

Intraseasonal Oscillation ◽

Sensitivity Study ◽

Ocean Model ◽

Surface Fluxes ◽

Boreal Winter ◽

Layer Depth ◽

Idealized Model

Abstract Sensitivity of tropical intraseasonal variability to mixed layer depth is examined in the modified National Center for Atmospheric Research Community Atmosphere Model 2.0.1 (CAM), with relaxed Arakawa–Schubert convection, coupled to a slab ocean model (SOM) whose mixed layer depth is fixed and geographically uniform, but varies from one experiment to the next. Intraseasonal west Pacific precipitation variations during boreal winter are enhanced relative to a fixed-SST (infinite mixed layer depth) simulation for mixed layer depths from 5 to 50 m, with a maximum at 20 m [interestingly, near the observed value in the regions where the Madden– Julian oscillation (MJO) is active], but are strongly diminished in the 2-m depth simulation. This nonmonotonicity of intraseasonal precipitation variance with respect to mixed layer depth was predicted by Sobel and Gildor using a highly idealized model. Further experiments with the same idealized model help to interpret results derived from the modified NCAR CAM. A sensitivity study shows that the convection–surface flux feedback [wind-induced surface heat exchange (WISHE)] is important to the intraseasonal variability in the CAM. This helps to explain the behavior of the 2-m SOM simulation and the agreement with the idealized model. Although intraseasonal SST variations are stronger in the 2-m SOM simulation than in any of the other simulations, these SST variations are phased in such a way as to diminish the amplitude of equatorial latent heat flux variations. Reducing the mixed layer depth is thus nearly equivalent to eliminating WISHE, which in this model reduces intraseasonal variability. The WISHE mechanism in the model is nonlinear and occurs in a region of mean low-level westerlies. Since a very shallow mixed layer is effectively similar to wet land, it is suggested that the mechanism described here may explain the local minimum in MJO amplitude observed over the Maritime Continent region.

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