Asymmetry of the Indian Ocean Dipole. Part II: Model Diagnosis*

2008 ◽  
Vol 21 (18) ◽  
pp. 4849-4858 ◽  
Author(s):  
Chi-Cherng Hong ◽  
Tim Li ◽  
Jing-Jia Luo
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Indian Ocean Dipole ◽  
Heat Budget ◽  
Coupled Model ◽  
Sensitivity Experiment ◽  
Negative Skewness ◽  
Model Diagnosis

Abstract In this second part of a two-part paper, the mechanism for the amplitude asymmetry of SST anomalies (SSTA) between positive and negative Indian Ocean dipole (IOD) events is investigated through the diagnosis of coupled model simulations. Same as the observed in Part I, a significant negative skewness appears in the IOD east pole (IODE) in September–November (SON), whereas there is no significant skewness in the IOD west pole (IODW). A sensitivity experiment shows that the negative skewness in IODE appears even in the case when the ENSO is absent. The diagnosis of the model mixed layer heat budget reveals that the negative skewness is primarily induced by the nonlinear ocean temperature advection and the asymmetry of the cloud–radiation–SST feedback, consistent with the observation (Part I). However, the simulated latent heat flux anomaly is greatly underestimated in IODE during the IOD developing stage [June–September (JJAS)]. As a result, the net surface heat flux acts as strong thermal damping. The underestimation of the latent heat flux anomaly in the IODE is probably caused by the westward shift of along-coast wind anomalies off Sumatra.

scholarly journals Asymmetry of the Indian Ocean Dipole. Part I: Observational Analysis

2008 ◽  
Vol 21 (18) ◽  
pp. 4834-4848 ◽  
Author(s):  
Chi-Cherng Hong ◽  
Tim Li ◽  
LinHo ◽  
Jong-Seong Kug
Keyword(s):  
Indian Ocean ◽  
Mixed Layer ◽  
Indian Ocean Dipole ◽  
Heat Budget ◽  
Mature Phase ◽  
Budget Analysis ◽  
Nonlinear Advection ◽  
Negative Skewness ◽  
The Indian Ocean ◽  
The Asymmetry

The physical mechanism for the amplitude asymmetry of SST anomalies (SSTA) between the positive and negative phases of the Indian Ocean dipole (IOD) is investigated, using Simple Ocean Data Assimilation (SODA) and NCAR–NCEP data. It is found that a strong negative skewness appears in the IOD east pole (IODE) in the mature phase [September–November (SON)], while the skewness in the IOD west pole is insignificant. Thus, the IOD asymmetry is primarily caused by the negative skewness in IODE. A mixed-layer heat budget analysis indicates that the following two air–sea feedback processes are responsible for the negative skewness. The first is attributed to the asymmetry of the wind stress–ocean advection–SST feedback. During the IOD developing stage [June–September (JJAS)], the ocean linear advection tends to enhance the mixed-layer temperature tendency, while nonlinear advection tends to cool the ocean in both the positive and negative events, thus contributing to the negative skewness in IODE. The second process is attributed to the asymmetry of the SST–cloud–radiation (SCR) feedback. For a positive IODE, the negative SCR feedback continues with the increase of warm SSTA. For a negative IODE, the same negative SCR feedback works when the amplitude of SSTA is small. After reaching a critical value, the cold SSTA may completely suppress the mean convection and lead to cloud free conditions; a further drop of the cold SSTA does not lead to additional thermal damping so that the cold SSTA may grow faster. A wind–evaporation–SST feedback may further amplify the asymmetry induced by the aforementioned nonlinear advection and SCR feedback processes.

scholarly journals Simulated Seasonal and Interannual Variability of the Mixed Layer Heat Budget in the Northern Indian Ocean*

2007 ◽  
Vol 20 (13) ◽  
pp. 3249-3268 ◽  
Author(s):  
Clémentde Boyer Montégut ◽  
Jérôme Vialard ◽  
S. S. C. Shenoi ◽  
D. Shankar ◽  
Fabien Durand ◽  
...  
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Interannual Variability ◽  
Latent Heat Flux ◽  
Mixed Layer ◽  
Heat Budget ◽  
Northern Indian Ocean ◽  
Solar Heat ◽  
Mixed Layer Heat Budget ◽  
Solar Heat Flux

Abstract A global ocean general circulation model (OGCM) is used to investigate the mixed layer heat budget of the northern Indian Ocean (NIO). The model is validated against observations and shows fairly good agreement with mixed layer depth data in the NIO. The NIO has been separated into three subbasins: the western Arabian Sea (AS), the eastern AS, and the Bay of Bengal (BoB). This study reveals strong differences between the western and eastern AS heat budget, while the latter basin has similarities with the BoB. Interesting new results on seasonal time scales are shown. The penetration of solar heat flux needs to be taken into account for two reasons. First, an average of 28 W m−2 is lost beneath the mixed layer over the year. Second, the penetration of solar heat flux tends to reduce the effect of solar heat flux on the SST seasonal cycle in the AS because the seasons of strongest flux are also seasons with a thin mixed layer. This enhances the control of SST seasonal variability by latent heat flux. The impact of salinity on SST variability is demonstrated. Salinity stratification plays a clear role in maintaining a high winter SST in the BoB and eastern AS while not in the western AS. The presence of freshwater near the surface allows heat storage below the surface layer that can later be recovered by entrainment warming during winter cooling (with a winter contribution of +2.1°C in the BoB). On an interannual time scale, the eastern AS and BoB are strongly controlled by the winds through the latent heat flux anomalies. In the western AS, vertical processes, as well as horizontal advection, contribute significantly to SST interannual variability, and the wind is not the only factor controlling the heat flux forcing.

scholarly journals Variational Computation of Sensible and Latent Heat Flux over Lake Superior

2018 ◽  
Vol 19 (2) ◽  
pp. 351-373
Author(s):  
Zuohao Cao ◽  
Murray D. Mackay ◽  
Christopher Spence ◽  
Vincent Fortin
Keyword(s):  
Heat Flux ◽  
Variational Method ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Gradient Method ◽  
Lake Superior ◽  
Coupled Model ◽  
Bowen Ratio ◽  
Heat Fluxes ◽  
Flux Gradient

Abstract Sensible and latent heat fluxes over Lake Superior are computed using a variational approach with a Bowen ratio constraint and inputs of 7 years of half-hourly temporal resolution observations of hydrometeorological variables over the lake. In an advancement from previous work focusing on the sensible heat flux, in this work computations of the latent heat flux are required so that a new physical constraint of the Bowen ratio is introduced. Verifications are made possible for fluxes predicted by a Canadian operational coupled atmosphere–ocean model due to recent availabilities of observed and model-predicted fluxes over Lake Superior. The observed flux data with longer time periods and higher temporal resolution than those used in previous studies allows for the examination of detailed performances in computing these fluxes. Evaluations utilizing eddy-covariance measurements over Lake Superior show that the variational method yields higher correlations between computed and measured sensible and latent heat fluxes than a flux-gradient method. The variational method is more accurate than the flux-gradient method in computing these fluxes at annual, monthly, daily, and hourly time scales. Under both unstable and stable conditions, the variational method considerably reduces mean absolute errors produced by the flux-gradient approach in computing the fluxes. It is demonstrated with 2 months of data that the variational method obtains higher correlation coefficients between the observed and the computed sensible and latent heat fluxes than the coupled model predicted, and yields lower mean absolute errors than the coupled model. Furthermore, comparisons are made between the coupled-model-predicted fluxes and the fluxes computed based on three buoy observations over Lake Superior.

scholarly journals How Does El Niño Affect Predictability Barrier of Its Accompanied Positive Indian Ocean Dipole Event?

2021 ◽  
Vol 9 (11) ◽  
pp. 1169
Author(s):  
Da Liu ◽  
Wansuo Duan ◽  
Rong Feng
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Latent Heat Flux ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
Sea Temperature ◽  
Positive Indian Ocean Dipole ◽  
Initial Errors ◽  
Temperature Errors

The effects of El Niño on the predictability of positive Indian Ocean dipole (pIOD) events are investigated by using the GFDL CM2p1 coupled model from the perspective of error growth. The results show that, under the influence of El Niño, the summer predictability barrier (SPB) for pIOD tends to intensify and the winter predictability barrier (WPB) is weakened. Since the reason for the weakening of WPB has been explained in a previous study, the present study attempts to explore why the SPB is enhanced. The results demonstrate that the initial sea temperature errors, which are most likely to induce SPB for pIOD with El Niño, possess patterns similar to those for pIOD without El Niño, whose dominant errors concentrate in the tropical Pacific Ocean (PO), with a pattern of negative SST errors occurring in the eastern and central PO and subsurface sea temperature errors being negative in the eastern PO and positive in the western PO. By tracking the development of such initial errors, it is found that the initial errors over PO lead to anomalous westerlies in the southeastern Indian Ocean (IO) through the effect of double-cell Walker circulation. Such westerly anomalies are inhibited by the strongest climatological easterly wind and the southeasterlies related to the pIOD event itself in summer, while they are enhanced by El Niño. This competing effect causes the intensified seasonal variation in latent heat flux, with much less loss in summer under the effect of El Niño. The greater suppression of the loss of latent heat flux favors the positive sea surface temperature (SST) errors developing much faster in the eastern Indian Ocean in summer, and eventually induces an enhanced SPB for pIOD due to El Niño.

Estimation of latent heat flux using satellite based observations over the North Indian Ocean

2016 ◽  
Author(s):  
Purnachand Ch. ◽  
V. Rao M. ◽  
Prasad K. V. S. R. ◽  
K. H. Rao ◽  
V. K. Dadhwal
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
North Indian Ocean ◽  
The North

scholarly journals Decadal Modulations of the Indian Ocean Dipole in the SINTEX-F1 Coupled GCM

2007 ◽  
Vol 20 (13) ◽  
pp. 2881-2894 ◽  
Author(s):  
Tomoki Tozuka ◽  
Jing-Jia Luo ◽  
Sebastien Masson ◽  
Toshio Yamagata
Keyword(s):  
Indian Ocean ◽  
Heat Transport ◽  
Indian Ocean Dipole ◽  
Decadal Variability ◽  
Heat Budget ◽  
Coupled Model ◽  
Tropical Indian Ocean ◽  
Decadal Modulation ◽  
Mascarene High ◽  
Budget Analysis

Abstract The decadal variation in the tropical Indian Ocean is investigated using outputs from a 200-yr integration of the Scale Interaction Experiment-Frontier Research Center for Global Change (SINTEX-F1) ocean–atmosphere coupled model. The first EOF mode of the decadal bandpass- (9–35 yr) filtered sea surface temperature anomaly (SSTA) represents a basinwide mode and is closely related with the Pacific ENSO-like decadal variability. The second EOF mode shows a clear east–west SSTA dipole pattern similar to that of the interannual Indian Ocean dipole (IOD) and may be termed the decadal IOD. However, it is demonstrated that the decadal air–sea interaction in the Tropics can be a statistical artifact; it should be interpreted more correctly as decadal modulation of interannual IOD events (i.e., asymmetric or skewed occurrence of positive and negative events). Heat budget analysis has revealed that the occurrence of IOD events is governed by variations in the southward Ekman heat transport across 15°S and variations in the Indonesian Throughflow associated with the ENSO. The variations in the southward Ekman heat transport are related to the Mascarene high activities.

The Potential Roles of Background Surface Wind in the SST Variability Associated with Intraseasonal Oscillations

2014 ◽  
Vol 27 (18) ◽  
pp. 7053-7068 ◽  
Author(s):  
Kaya Kanemaru ◽  
Hirohiko Masunaga
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Heat Budget ◽  
Surface Wind ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Westerly Wind ◽  
Sst Variability ◽  
Intraseasonal Oscillations

Abstract The current study is aimed at exploring the potential roles of the seasonally altering background surface wind in the seasonality of the intraseasonal oscillations (ISOs) with a focus on the sea surface temperature (SST) variability. A composite analysis of the ocean mixed layer heat budget in term of ISO phases with various satellite data is performed for boreal winter and summer. The scalar wind is found to be a dominant factor that accounts for the ocean surface heat budget, implying that the background surface wind as well as its anomaly is important for the SST variability. An easterly anomaly to the east of convection diminishes scalar wind, and thus latent heat flux, when superposed onto a background westerly wind, implying that the presence of basic westerly wind is important for the development of a warm SST anomaly ahead of the ISO convection. On the other hand, an easterly anomaly in combination with basic easterly wind magnifies scalar wind and latent heat flux and cancels out the shortwave heat flux anomaly. The seasonal migration of the background westerly wind, which is confined to a southern equatorial belt in boreal winter but spread across the northern Indian Ocean in boreal summer, may offer a mechanism that partly accounts for the seasonal characteristics of ISO propagation. The northward propagation of the SST variability associated with the boreal summer ISO is found to also involve a similar mechanism with the meridional wind modulation of scalar wind.

scholarly journals Intraseasonal Latent Heat Flux Based on Satellite Observations

2009 ◽  
Vol 22 (17) ◽  
pp. 4539-4556 ◽  
Author(s):  
Semyon A. Grodsky ◽  
Abderrahim Bentamy ◽  
James A. Carton ◽  
Rachel T. Pinker
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Mixed Layer ◽  
Heat Budget ◽  
Mixed Layer Depth ◽  
Intraseasonal Variability ◽  
Surface Fluxes ◽  
Tropical Region ◽  
Surprising Result

Abstract Weekly average satellite-based estimates of latent heat flux (LHTFL) are used to characterize spatial patterns and temporal variability in the intraseasonal band (periods shorter than 3 months). As expected, the major portion of intraseasonal variability of LHTFL is due to winds, but spatial variability of humidity and SST are also important. The strongest intraseasonal variability of LHTFL is observed at the midlatitudes. It weakens toward the equator, reflecting weak variance of intraseasonal winds at low latitudes. It also decreases at high latitudes, reflecting the effect of decreased SST and the related decrease of time-mean humidity difference between heights z = 10 m and z = 0 m. Within the midlatitude belts the intraseasonal variability of LHTFL is locally stronger (up to 50 W m−2) in regions of major SST fronts (like the Gulf Stream and Agulhas). Here it is forced by passing storms and is locally amplified by unstable air over warm SSTs. Although weaker in amplitude (but still significant), intraseasonal variability of LHTFL is observed in the tropical Indian and Pacific Oceans due to wind and humidity perturbations produced by the Madden–Julian oscillations. In this tropical region intraseasonal LHTFL and incoming solar radiation vary out of phase so that evaporation increases just below the convective clusters. Over much of the interior ocean where the surface heat flux dominates the ocean mixed layer heat budget, intraseasonal SST cools in response to anomalously strong upward intraseasonal LHTFL. This response varies geographically, in part because of geographic variations of mixed layer depth and the resulting variations in thermal inertia. In contrast, in the eastern tropical Pacific and Atlantic cold tongue regions intraseasonal SST and LHTFL are positively correlated. This surprising result occurs because in these equatorial upwelling areas SST is controlled by advection rather than by surface fluxes. Here LHTFL responds to rather than drives SST.

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