scholarly journals Impact of the Diurnal Cycle of Solar Radiation on Intraseasonal SST Variability in the Western Equatorial Pacific

2005 ◽  
Vol 18 (14) ◽  
pp. 2628-2636 ◽  
Author(s):  
Toshiaki Shinoda
Keyword(s):  
Solar Radiation ◽  
Mixed Layer ◽  
Diurnal Cycle ◽  
Intraseasonal Oscillation ◽  
Warm Pool ◽  
Surface Fluxes ◽  
Surface Cooling ◽  
Mixing Processes ◽  
Surface Warming ◽  
Sst Variability

Abstract The mechanism by which the diurnal cycle of solar radiation modulates intraseasonal SST variability in the western Pacific warm pool is investigated using a one-dimensional mixed layer model. SSTs in the model experiments forced with hourly surface fluxes during the calm–sunny phase of intraseasonal oscillation are significantly warmer than those with daily mean surface fluxes. The difference in two experiments is explained by upper-ocean mixing processes during nighttime. Surface warming during daytime creates a shallow diurnal warm layer near the surface (0–3 m), which can be easily eroded by surface cooling during nighttime. Further cooling, however, requires a substantial amount of energy because deeper waters need to be entrained into the mixed layer. Since the shallow diurnal layer is not formed in the experiment with daily mean surface fluxes, the SST for the hourly forcing case is warmer most of the time due to the diurnally varying solar radiation. Sensitivity of the intraseasonal SST variation to the penetrative component of solar radiation is examined, showing that the diurnal cycle plays an important role in the sensitivity. Solar radiation absorbed in the upper few meters significantly influences intraseasonal SST variations through changes in amplitude of diurnal SST variation.

scholarly journals Characterization of distinct bloom phenology regimes in the Southern Ocean

2015 ◽  
Vol 72 (6) ◽  
pp. 1985-1998 ◽  
Author(s):  
Jean-Baptiste Sallée ◽  
J. Llort ◽  
A. Tagliabue ◽  
M. Lévy
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Encounter Rate ◽  
Surface Cooling ◽  
Winter Solstice ◽  
Surface Warming ◽  
Colour Measurements ◽  
Circumpolar Current ◽  
Biomass Increase

Abstract In this study, we document the regional variations of bloom phenology in the Southern Ocean, based on a 13-year product of ocean colour measurements co-located with observation-based estimates of the mixed-layer depth. One key aspect of our work is to discriminate between mixed-layer integrated blooms and surface blooms. By segregating blooms that occur before or after the winter solstice and blooms where integrated and surface biomass increase together or display a lag, we define three dominating Southern Ocean bloom regimes. While the regime definitions are solely based on bloom timing characteristics, the three regimes organize coherently in geographical space, and are associated with distinct dynamical regions of the Southern Ocean: the subtropics, the subantarctic, and the Antarctic Circumpolar Current region. All regimes have their mixed-layer integrated onset between autumn and winter, when the daylength is short and the mixed layer actively mixes and deepens. We discuss how these autumn–winter bloom onsets are controlled by either nutrient entrainment and/or reduction in prey-grazer encounter rate. In addition to the autumn–winter biomass increase, the subantarctic regime has a significant spring biomass growth associated with the shutdown of turbulence when air–sea heat flux switches from surface cooling to surface warming.

Winter Extreme Mixed Layer Depth South of the Kuroshio Extension

2020 ◽  
Vol 33 (24) ◽  
pp. 10419-10436
Author(s):  
Jingjie Yu ◽  
Bolan Gan ◽  
Zhao Jing ◽  
Lixin Wu
Keyword(s):  
Heat Flux ◽  
Mixed Layer ◽  
Kuroshio Extension ◽  
Mixed Layer Depth ◽  
Surface Cooling ◽  
Layer Depth ◽  
Mode Water ◽  
Surface Warming ◽  
Mechanical Stirring ◽  
The Kuroshio

AbstractChange in the extratropical wintertime-mean mixed layer has been widely studied, given its importance to both physical and biogeochemical processes. With a focus on the south of the Kuroshio Extension region where the mixed layer is deepest in March, this study shows that variation of the synoptic-scale extreme mixed layer depth (MLD) is a better precursor than the monthly mean (or nonextreme) MLD for change in the subtropical mode water formation in spring, based on the NCEP Climate Forecast System Reanalysis (1979–2010). It is found that the extreme MLD events are attributable to the accumulation of excessive surface cooling driven by the synoptic storms that characterize cold-air outbreaks. Particularly, the difference between the extreme and nonextreme MLD is primarily related to differences in the cumulative synoptic heat flux anomalies, while a change in the preconditioning upper-ocean stratification contributes almost equally to both cases. Relative contributions of oceanic and atmospheric forcing to the interannual variation of the extreme MLD are quantified using a bulk mixed layer model. Results show comparable contributions: the preconditioning stratification change accounts for ~44% of total variance of the extreme MLD, whereas the convective mixing by surface heat flux and the mechanical stirring by wind stress account for ~35% and ~13%, respectively. In addition, both the reanalysis and observational data reveal that the extreme and nonextreme MLD has been shallowed significantly during 1979–2010, which is accounted for by the strengthened stratification due to the enhanced ocean surface warming by the Kuroshio heat transport.

scholarly journals Impact of the Ocean Mixed Layer Diurnal Variations on the Intraseasonal Variability of Sea Surface Temperatures in the Atlantic Ocean*

2011 ◽  
Vol 24 (12) ◽  
pp. 2889-2914 ◽  
Author(s):  
Virginie Guemas ◽  
David Salas-Mélia ◽  
Masa Kageyama ◽  
Hervé Giordani ◽  
Aurore Voldoire
Keyword(s):  
Heat Flux ◽  
Atlantic Ocean ◽  
Surface Temperature ◽  
Wind Stress ◽  
Mixed Layer ◽  
Diurnal Variations ◽  
Surface Fluxes ◽  
Sea Surface ◽  
Sst Variability ◽  
The Tropics

Abstract This study investigates the nonlinear processes by which the ocean diurnal variations can affect the intraseasonal sea surface temperature (SST) variability in the Atlantic Ocean. The Centre National de Recherches Météorologiques one-dimensional ocean model (CNRMOM1D) is forced with the 40-yr ECMWF Re-Analysis (ERA-40) surface fluxes with a 1-h frequency in solar heat flux in a first simulation and with a daily forcing frequency in a second simulation. This model has a vertical resolution of 1 m near the surface. The comparison between both experiments shows that the daily mean surface temperature is modified by about 0.3°–0.5°C if the ocean diurnal variations are represented, and this correction can persist for 15–40 days in the midlatitudes and more than 60 days in the tropics. The so-called rectification mechanism, by which the ocean diurnal warming enhances the intraseasonal SST variability by 20%–40%, is found to be robust in the tropics. In contrast, in the midlatitudes, diurnal variations in wind stress and nonsolar heat flux are shown to affect the daily mean SST. For example, an intense wind stress or nonsolar heat flux toward the atmosphere during the first half of the day followed by weak fluxes during the second half result in a shallow mixed layer. The following day, the preconditioning results in heat being trapped near the surface and the daily mean surface temperature being higher than if these diurnal variations in surface forcings were not resolved.

scholarly journals Effects of the diurnal cycle in solar radiation on the tropical Indian Ocean mixed layer variability during wintertime Madden-Julian Oscillations

2013 ◽  
Vol 118 (10) ◽  
pp. 4945-4964 ◽  
Author(s):  
Yuanlong Li ◽  
Weiqing Han ◽  
Toshiaki Shinoda ◽  
Chunzai Wang ◽  
Ren-Chieh Lien ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Solar Radiation ◽  
Mixed Layer ◽  
Diurnal Cycle ◽  
Tropical Indian Ocean ◽  
Ocean Mixed Layer

scholarly journals Mixed Layer Depth and Sea Surface Warming under Diurnally Cycling Surface Heat Flux in the Heating Season

2019 ◽  
Vol 49 (7) ◽  
pp. 1769-1787 ◽  
Author(s):  
Yusuke Ushijima ◽  
Yutaka Yoshikawa
Keyword(s):  
Mixed Layer ◽  
Diurnal Cycle ◽  
Surface Heat Flux ◽  
Mixed Layer Depth ◽  
Surface Heat ◽  
Sea Surface ◽  
Heating Season ◽  
Layer Depth ◽  
Surface Warming ◽  
Latitudinal Dependence

AbstractIn the present study, large-eddy simulations (LESs) were performed to investigate mixed layer depth (MLD) and sea surface warming (SSW) under diurnally cycling surface heat flux in the heating season, in which a mixed layer (ML) is shoaling on intraseasonal time scales. The LES results showed that the diurnal cycle makes the MLD greater (smaller) at lower (higher) latitudes than the MLD without the cycle. Time scales of the wind-induced shear and the surface heat are a key to understand this latitudinal dependence of the diurnal cycle effects. The wind-induced shear-driven turbulence developed from early morning and became strongest at half the inertial period (Ti/2), while nighttime cooling weakened the ML stratification until the end of the nighttime (T24 = 24 h). At lower latitudes where Ti/2 > T24 (lower than 15°), the shear-driven turbulence continued to grow after T24 and determined the time of the greatest MLD. Thus, the shear-driven turbulence shaped the latitudinal dependence of the MLD, though convective turbulence helped further deepening of the ML. At higher latitudes (Ti/2 < T24), on the other hand, the shear-driven turbulence ceased growing before the nighttime cooling ended. However, reduced stratification due to the nighttime cooling supported the shear-driven turbulence to continue deepening the ML. Thus, the nighttime cooling shaped the latitudinal dependence of the MLD at higher latitudes. The MLD change induced by the diurnal cycle altered the SSW rate. At higher latitudes, the diurnal cycle is expected to reduce the MLD and increase the SSW by 10% in the heating season.

Surface Fluxes and Ocean Coupling in the Tropical Intraseasonal Oscillation

2004 ◽  
Vol 17 (22) ◽  
pp. 4368-4386 ◽  
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.

Mixed Layer Models and Their Application to Water Quality Problems

1994 ◽  
Vol 29 (2-3) ◽  
pp. 221-232
Author(s):  
M.J. McCormick
Keyword(s):  
Water Quality ◽  
Mixed Layer ◽  
Thermal Structure ◽  
Mass Conservation ◽  
Eddy Diffusion ◽  
Rate Of Change ◽  
Surface Mixed Layer ◽  
Storm Events ◽  
Quality Model ◽  
Mixing Processes

Abstract Four one-dimensional models which have been used to characterize surface mixed layer (ML) processes and the thermal structure are described. Although most any model can be calibrated to mimic surface water temperatures, it does not imply that the corresponding mixing processes are well described. Eddy diffusion or "K" models can exhibit this problem. If a ML model is to be useful for water quality applications, then it must be able to resolve storm events and, therefore, be able to simulate the ML depth, h, and its time rate of change, dh/dt. A general water quality model is derived from mass conservation principles to demonstrate how ML models can be used in a physically meaningful way to address water quality issues.

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.

Mixed layer modeling in the East Pacific warm pool during 2002

2011 ◽  
Vol 38 (11-12) ◽  
pp. 2559-2573 ◽  
Author(s):  
Luke P. Van Roekel ◽  
Eric D. Maloney
Keyword(s):  
Mixed Layer ◽  
Warm Pool ◽  
East Pacific ◽  
Pacific Warm Pool
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