22 A new observational record of upper-ocean currents at 15°N on the western coast of 23 India is... more 22 A new observational record of upper-ocean currents at 15°N on the western coast of 23 India is dominated by intraseasonal (55−110 day) variations of alongshore currents, 24 whereas sea level at the same location has a clear seasonal signal. These observations can 25 be interpreted within the framework of linear wave theory. At 15°N,the minimum period 26 for
Journal of Atmospheric and Oceanic Technology, 2014
The upper few meters of the ocean form a critical layer for air-sea interaction, but because of o... more The upper few meters of the ocean form a critical layer for air-sea interaction, but because of observational challenges this region is undersampled. However, the physical processes controlling momentum transfer, gas exchange, and heat transfer are all concentrated in the uppermost region of the ocean. To study this region, the Air-Sea Interaction Profiler (ASIP) was developed. This is an autonomous microstructure vertical profiling instrument that provides data from a maximum depth of 100 m to the ocean surface and allows measurements to be performed in an undisturbed environment. The core sensor package on ASIP includes shear probes, microstructure and CTD-quality temperature and conductivity sensors, a photosynthetically active radiation (PAR) sensor, and an oxygen optode providing a repeated high-resolution dataset immediately below the air-sea interface. Autonomous profiling is accomplished with thrusters that submerge the positively buoyant instrument. Once the desired depth is reached, ASIP ascends through the water column acquiring data. At the surface, ASIP acquires its position and transmits this over the Iridium satellite network. ASIP is then placed in a low-power mode for a specified period, whereupon it repeats the profile cycle. Two-way communication over the Iridium network allows mission parameters to be changed in real time. ASIP has been used to study several scientific questions, such as the impact of diurnal warming on atmospheric processes, turbulence scaling in the upper ocean, parameterizing air-sea gas exchange, salinity gradients in the ocean surface boundary layer (OSBL), and consequences for remote sensing. @ Current affiliation:
Deep Sea Research Part I: Oceanographic Research Papers, 2014
An autonomous upwardly-moving microstructure profiler was used to collect measurements of the rat... more An autonomous upwardly-moving microstructure profiler was used to collect measurements of the rate of dissipation of turbulent kinetic energy (ε) in the tropical Indian Ocean during a single diurnal cycle, from about 50 m depth to the sea surface. This dataset is one of only a few to resolve upper ocean ε over a diurnal cycle from below the active mixing layer up to the air-sea interface. Wind speed was weak with an average value of $ 5 m s À 1 and the wave field was swell-dominated. Within the wind and wave affected surface layer (WWSL), ε values were on the order of 10 À 7 -10 À 6 W kg À 1 at a depth of 0.75 m and when averaged, were almost a factor of two above classical law of the wall theory, possibly indicative of an additional source of energy from the wave field. Below this depth, ε values were closer to wall layer scaling, suggesting that the work of the Reynolds stress on the wind-induced vertical shear was the major source of turbulence within this layer. No evidence of persistent elevated near-surface ε characteristic of wave-breaking conditions was found. Profiles collected during night-time displayed relatively constant ε values at depths between the WWSL and the base of the mixing layer, characteristic of mixing by convective overturning. Within the remnant layer, depth-averaged values of ε started decaying exponentially with an e-folding time of 47 min, about 30 min after the reversal of the total surface net heat flux from oceanic loss to gain.
ABSTRACT The present study describes the observed sea surface salinity (SSS) interannual variabil... more ABSTRACT The present study describes the observed sea surface salinity (SSS) interannual variability in the Bay of Bengal over the 2009–2014 period. It is based on an original compilation of all available in situ SSS observations in that region, assembled in a 2°-resolution trimonthly gridded field. We find that year-to-year SSS variability is particularly strong in the north-eastern part of the bay. Over recent years, this variability takes the form of two successive and opposite phases: a saltening phase from mid-2009 to late 2010, immediately followed by a freshening phase from late 2010 to late 2011. The typical magnitude of each anomalous spell is about one in the practical salinity scale, making this area one of the most variable of the tropical oceans at interannual timescales. A simple mixed-layer salt budget indicates that year-to-year large-scale SSS variability in the Northern Bay of Bengal is primarily driven by freshwater flux variability with a correlation of 0.68, with rather independent contributions from precipitation and river run-off. The oceanic surface circulation variability contributes less systematically to the large-scale SSS evolution in the Northern Bay of Bengal over the entire record with a correlation of 0.13, despite a strong contribution at times, in particular, during the 2011 positive Indian Ocean Dipole (IOD) freshening.
Determine the factors that control the Sea Surface Temperature (SST) in the east- ern Pacific is ... more Determine the factors that control the Sea Surface Temperature (SST) in the east- ern Pacific is important to improve our understanding of the coupling between the atmosphere and ocean. Tropical Instability Waves (TIWs) play an important role in the heat budget of the upper eastern Pacific. Recent observations have suggested that TIWs have an imprint in the Planetary Boundary Layer (PBL). A series of numerical experiments are carried out to study the ocean-atmosphere interactions of the TIW generated in the equatorial eastern Pacific region using an Ocean General Circulation Model (OGCM) coupled to a 1-D PBL model. For this study, the oceanic model OPA is coupled with the 1-D PBL model used in the European Centre for Medium Range Forecast (ECMWF) numerical weather forecast model. The PBL scheme provides an estimate of the surface wind stress, based on the ocean model SST, and specified cli- matologies of wind, air temperature and humidity at 925 hPa. This scheme is used in both one ...
... Since synoptic atmospheric variability can affect the SST field, through the paradigm of inte... more ... Since synoptic atmospheric variability can affect the SST field, through the paradigm of integrated noise in midlatitudes (Frankignoul and Hasselmann 1977) and through westerly wind burstsfor example, in the case of El Niño (eg, McPhaden 1999)there is a source of ...
This paper is an evaluation of the role of salinity in the framework of temperature data assimila... more This paper is an evaluation of the role of salinity in the framework of temperature data assimilation in a global ocean model that is used to initialize seasonal climate forecasts. It is shown that the univariate assimilation of temperature profiles, without attempting to correct salinity, can induce first-order errors in the subsurface temperature and salinity fields. A recently developed scheme by A. Troccoli and K. Haines is used to improve the salinity field. In this scheme, salinity increments are derived from the observed temperature, by using the model temperature and salinity profiles, assuming that the temperature-salinity relationship in the model profiles is preserved. In addition, the temperature and salinity fields are matched below the observed temperature profile by vertically displacing the original model profiles.
ABSTRACT AbstractPrevious studies have investigated how second-baroclinic-mode (n = 2) Kelvin and... more ABSTRACT AbstractPrevious studies have investigated how second-baroclinic-mode (n = 2) Kelvin and Rossby waves in the equatorial Indian Ocean (IO) interact to form basin resonances at the semiannual (180 day) and 90-day periods. This paper examines unresolved issues about these resonances, including the reason the 90-day resonance is concentrated in the eastern ocean, the time scale for their establishment, and the impact of complex basin geometry. A hierarchy of ocean models is used: an idealized one-dimensional (1D) model, a linear continuously stratified ocean model (LCSM), and an ocean general circulation model (OGCM) forced by Quick Scatterometer (QuikSCAT) wind during 2000–08. Results indicate that the eastern-basin concentration of the 90-day resonance happens because the westward-propagating Rossby wave is slower, and thus is damped more than the eastward-propagating Kelvin wave. Results also indicate that superposition with other baroclinic modes further enhances the eastern maximum and weakens sea level ...
Optimal perturbations of sea surface salinity are obtained for an idealized North Atlantic basin ... more Optimal perturbations of sea surface salinity are obtained for an idealized North Atlantic basin using a 3D planetary geostrophic model-optimality is defined with respect to the intensity of the meridional overturning circulation. Both optimal initial and stochastic perturbations are computed in two experiments corresponding to two different formulations of the surface boundary conditions: the first experiment uses mixed boundary conditions (i.e., restoring surface temperature and prescribed freshwater flux), whereas the second experiment uses flux boundary conditions for both temperature and salinity. The latter reveals greater responses to both initial and stochastic perturbations that are related to the existence of a weakly damped oscillatory eigenmode of the Jacobian matrix, the optimal perturbations being closely related to its biorthogonal. The optimal initial perturbation induces a transient modification of the circulation after 24 yr. The spectral response to the optimal stochastic perturbation reveals a strong peak at 35 yr, corresponding to the period of this oscillatory eigenmode. This study provides an upper bound of the meridional overturning response at multidecadal time scales to freshwater flux perturbation: for typical amplitudes of Great Salinity Anomalies, initial perturbations can alter the circulation by 12.25 Sv (1 Sv [ 10 6 m 3 s 21 ; i.e., 12.5% of the mean circulation) at most; stochastic perturbations with amplitudes typical of the interannual variability of the freshwater flux in midlatitudes induce a circulation variability with a standard deviation of 1 Sv (i.e., 5.5% of the mean circulation) at most.
In this paper, the combined assimilation of satellite observed sea level anomalies and in situ te... more In this paper, the combined assimilation of satellite observed sea level anomalies and in situ temperature data into a global ocean model, which is used to initialize a coupled ocean-atmosphere forecast system, is described. The altimeter data are first used to create synthetic temperature observations, which are then combined with the directly observed temperature profiles in an optimum interpolation scheme. In addition to temperature, salinity is corrected based on a preservation of the model's local temperature-salinity relationship. Coupled forecasts with a lead time of up to 6 months are initialized from the ocean analyses and the impact of the data assimilation on both the ocean analysis and the coupled forecasts is investigated. It is shown that forecasts of sea surface temperature anomalies in the Niño-3 area can be improved by initializing the coupled forecast model with the ocean analysis in which temperature and altimeter data are assimilated in combination. The results further imply that a good simulation of the salinity field is required to make optimum use of the altimeter data.
A simple coupled model is used in a zonally symmetric aquaplanet configuration to investigate the... more A simple coupled model is used in a zonally symmetric aquaplanet configuration to investigate the effect of ocean-atmosphere coupling on the Asian monsoon intraseasonal oscillation. The model consists of a linear atmospheric model of intermediate complexity based on quasi-equilibrium theory coupled to a simple, linear model of the upper ocean. This model has one unstable eigenmode with a period in the 30-60-day range and a structure similar to the observed northward-propagating intraseasonal oscillation in the Bay of Bengal/west Pacific sector.
In the present study, interannual fluctuations of the mixed layer depth (MLD) in the tropical Ind... more In the present study, interannual fluctuations of the mixed layer depth (MLD) in the tropical Indian Ocean are investigated from a long-term eddy permitting numerical simulation and a new observational dataset built from hydrographic in situ data including Argo data . Both datasets show similar interannual variability patterns in relation with known climate modes and reasonable phase agreement in key regions. Due to the scarcity of the observational dataset, we then largely rely on the model to describe the interannual MLD variations in more detail. MLD interannual variability is two to four times smaller than the seasonal cycle. A large fraction of MLD interannual variations is linked to large-scale climate modes, with the exception of coastal and subtropical regions where interannual signature of small-scale structures dominates. The Indian Ocean Dipole is responsible for most variations in the 10°N-10°S band, with positive phases being associated with a shallow MLD in the equatorial and south-eastern Indian Ocean and a deepening in the south-central Indian Ocean. The El Niño signature is rather weak, with moderate MLD shoaling in autumn in the eastern Arabian Sea. Stronger than usual monsoon jets are only associated with a very modest MLD deepening in the southern Arabian Sea in summer. Finally, positive Indian Ocean Subtropical Dipoles are associated with a MLD deepening between 15 and 30°S. Buoyancy fluxes generally appear to dominate MLD interannual variations except for IOD-induced signals in the south-central Indian Ocean in autumn, where wind stirring and Ekman pumping dominate.
This presentation describes results from the Air-Sea Interaction Profiler (ASIP), an autonomous p... more This presentation describes results from the Air-Sea Interaction Profiler (ASIP), an autonomous profiling instrument for upper ocean measurements. The measurements from ASIP are well suited to enhancing research on air-sea interfacial and near surface processes. Autonomous profiling is accomplished with a thruster, which submerges ASIP to a programmed depth. Once this depth is reached the positively buoyant instrument will ascend
Journal of Advances in Modeling Earth Systems, 2014
This paper presents the NOW regional coupled ocean-atmosphere model built from the NEMO ocean and... more This paper presents the NOW regional coupled ocean-atmosphere model built from the NEMO ocean and WRF atmospheric numerical models. This model is applied to the tropical Indian Ocean, with the oceanic and atmospheric components sharing a common 1 =4 horizontal grid. Long experiments are performed over the 1990-2009 period using the Betts-Miller-Janjic (BMJ) and Kain-Fritsch (KF) cumulus parameterizations. Both simulations produce a realistic distribution of seasonal rainfall and a realistic northward seasonal migration of monsoon rainfall over the Indian subcontinent. At subseasonal time scales, the model reasonably reproduces summer monsoon active and break phases, although with underestimated rainfall and surface wind signals. Its relatively high resolution results in realistic spatial and seasonal distributions of tropical cyclones, but it fails to reproduce the strongest observed cyclone categories. At interannual time scales, the model reproduces the observed variability associated with the Indian Ocean Dipole (IOD) and the delayed basin-wide warming/cooling induced by the El Niño Southern Oscillation (ENSO). The timing of IOD occurrence in the model generally matches that of the observed events, confirming the influence of ENSO on the IOD development (through the effect of lateral boundary conditions in our simulations). Although the KF and BMJ simulations share a lot in common, KF strongly overestimates rainfall at all time scales. KF also overestimates the number of simulated cyclones by a factor two, while simulating stronger events (up to 55 m s 21 ) compared to BMJ (up to 40 m s 21 ). These results could be related to an overly active cumulus parameterization in KF.
22 A new observational record of upper-ocean currents at 15°N on the western coast of 23 India is... more 22 A new observational record of upper-ocean currents at 15°N on the western coast of 23 India is dominated by intraseasonal (55−110 day) variations of alongshore currents, 24 whereas sea level at the same location has a clear seasonal signal. These observations can 25 be interpreted within the framework of linear wave theory. At 15°N,the minimum period 26 for
Journal of Atmospheric and Oceanic Technology, 2014
The upper few meters of the ocean form a critical layer for air-sea interaction, but because of o... more The upper few meters of the ocean form a critical layer for air-sea interaction, but because of observational challenges this region is undersampled. However, the physical processes controlling momentum transfer, gas exchange, and heat transfer are all concentrated in the uppermost region of the ocean. To study this region, the Air-Sea Interaction Profiler (ASIP) was developed. This is an autonomous microstructure vertical profiling instrument that provides data from a maximum depth of 100 m to the ocean surface and allows measurements to be performed in an undisturbed environment. The core sensor package on ASIP includes shear probes, microstructure and CTD-quality temperature and conductivity sensors, a photosynthetically active radiation (PAR) sensor, and an oxygen optode providing a repeated high-resolution dataset immediately below the air-sea interface. Autonomous profiling is accomplished with thrusters that submerge the positively buoyant instrument. Once the desired depth is reached, ASIP ascends through the water column acquiring data. At the surface, ASIP acquires its position and transmits this over the Iridium satellite network. ASIP is then placed in a low-power mode for a specified period, whereupon it repeats the profile cycle. Two-way communication over the Iridium network allows mission parameters to be changed in real time. ASIP has been used to study several scientific questions, such as the impact of diurnal warming on atmospheric processes, turbulence scaling in the upper ocean, parameterizing air-sea gas exchange, salinity gradients in the ocean surface boundary layer (OSBL), and consequences for remote sensing. @ Current affiliation:
Deep Sea Research Part I: Oceanographic Research Papers, 2014
An autonomous upwardly-moving microstructure profiler was used to collect measurements of the rat... more An autonomous upwardly-moving microstructure profiler was used to collect measurements of the rate of dissipation of turbulent kinetic energy (ε) in the tropical Indian Ocean during a single diurnal cycle, from about 50 m depth to the sea surface. This dataset is one of only a few to resolve upper ocean ε over a diurnal cycle from below the active mixing layer up to the air-sea interface. Wind speed was weak with an average value of $ 5 m s À 1 and the wave field was swell-dominated. Within the wind and wave affected surface layer (WWSL), ε values were on the order of 10 À 7 -10 À 6 W kg À 1 at a depth of 0.75 m and when averaged, were almost a factor of two above classical law of the wall theory, possibly indicative of an additional source of energy from the wave field. Below this depth, ε values were closer to wall layer scaling, suggesting that the work of the Reynolds stress on the wind-induced vertical shear was the major source of turbulence within this layer. No evidence of persistent elevated near-surface ε characteristic of wave-breaking conditions was found. Profiles collected during night-time displayed relatively constant ε values at depths between the WWSL and the base of the mixing layer, characteristic of mixing by convective overturning. Within the remnant layer, depth-averaged values of ε started decaying exponentially with an e-folding time of 47 min, about 30 min after the reversal of the total surface net heat flux from oceanic loss to gain.
ABSTRACT The present study describes the observed sea surface salinity (SSS) interannual variabil... more ABSTRACT The present study describes the observed sea surface salinity (SSS) interannual variability in the Bay of Bengal over the 2009–2014 period. It is based on an original compilation of all available in situ SSS observations in that region, assembled in a 2°-resolution trimonthly gridded field. We find that year-to-year SSS variability is particularly strong in the north-eastern part of the bay. Over recent years, this variability takes the form of two successive and opposite phases: a saltening phase from mid-2009 to late 2010, immediately followed by a freshening phase from late 2010 to late 2011. The typical magnitude of each anomalous spell is about one in the practical salinity scale, making this area one of the most variable of the tropical oceans at interannual timescales. A simple mixed-layer salt budget indicates that year-to-year large-scale SSS variability in the Northern Bay of Bengal is primarily driven by freshwater flux variability with a correlation of 0.68, with rather independent contributions from precipitation and river run-off. The oceanic surface circulation variability contributes less systematically to the large-scale SSS evolution in the Northern Bay of Bengal over the entire record with a correlation of 0.13, despite a strong contribution at times, in particular, during the 2011 positive Indian Ocean Dipole (IOD) freshening.
Determine the factors that control the Sea Surface Temperature (SST) in the east- ern Pacific is ... more Determine the factors that control the Sea Surface Temperature (SST) in the east- ern Pacific is important to improve our understanding of the coupling between the atmosphere and ocean. Tropical Instability Waves (TIWs) play an important role in the heat budget of the upper eastern Pacific. Recent observations have suggested that TIWs have an imprint in the Planetary Boundary Layer (PBL). A series of numerical experiments are carried out to study the ocean-atmosphere interactions of the TIW generated in the equatorial eastern Pacific region using an Ocean General Circulation Model (OGCM) coupled to a 1-D PBL model. For this study, the oceanic model OPA is coupled with the 1-D PBL model used in the European Centre for Medium Range Forecast (ECMWF) numerical weather forecast model. The PBL scheme provides an estimate of the surface wind stress, based on the ocean model SST, and specified cli- matologies of wind, air temperature and humidity at 925 hPa. This scheme is used in both one ...
... Since synoptic atmospheric variability can affect the SST field, through the paradigm of inte... more ... Since synoptic atmospheric variability can affect the SST field, through the paradigm of integrated noise in midlatitudes (Frankignoul and Hasselmann 1977) and through westerly wind burstsfor example, in the case of El Niño (eg, McPhaden 1999)there is a source of ...
This paper is an evaluation of the role of salinity in the framework of temperature data assimila... more This paper is an evaluation of the role of salinity in the framework of temperature data assimilation in a global ocean model that is used to initialize seasonal climate forecasts. It is shown that the univariate assimilation of temperature profiles, without attempting to correct salinity, can induce first-order errors in the subsurface temperature and salinity fields. A recently developed scheme by A. Troccoli and K. Haines is used to improve the salinity field. In this scheme, salinity increments are derived from the observed temperature, by using the model temperature and salinity profiles, assuming that the temperature-salinity relationship in the model profiles is preserved. In addition, the temperature and salinity fields are matched below the observed temperature profile by vertically displacing the original model profiles.
ABSTRACT AbstractPrevious studies have investigated how second-baroclinic-mode (n = 2) Kelvin and... more ABSTRACT AbstractPrevious studies have investigated how second-baroclinic-mode (n = 2) Kelvin and Rossby waves in the equatorial Indian Ocean (IO) interact to form basin resonances at the semiannual (180 day) and 90-day periods. This paper examines unresolved issues about these resonances, including the reason the 90-day resonance is concentrated in the eastern ocean, the time scale for their establishment, and the impact of complex basin geometry. A hierarchy of ocean models is used: an idealized one-dimensional (1D) model, a linear continuously stratified ocean model (LCSM), and an ocean general circulation model (OGCM) forced by Quick Scatterometer (QuikSCAT) wind during 2000–08. Results indicate that the eastern-basin concentration of the 90-day resonance happens because the westward-propagating Rossby wave is slower, and thus is damped more than the eastward-propagating Kelvin wave. Results also indicate that superposition with other baroclinic modes further enhances the eastern maximum and weakens sea level ...
Optimal perturbations of sea surface salinity are obtained for an idealized North Atlantic basin ... more Optimal perturbations of sea surface salinity are obtained for an idealized North Atlantic basin using a 3D planetary geostrophic model-optimality is defined with respect to the intensity of the meridional overturning circulation. Both optimal initial and stochastic perturbations are computed in two experiments corresponding to two different formulations of the surface boundary conditions: the first experiment uses mixed boundary conditions (i.e., restoring surface temperature and prescribed freshwater flux), whereas the second experiment uses flux boundary conditions for both temperature and salinity. The latter reveals greater responses to both initial and stochastic perturbations that are related to the existence of a weakly damped oscillatory eigenmode of the Jacobian matrix, the optimal perturbations being closely related to its biorthogonal. The optimal initial perturbation induces a transient modification of the circulation after 24 yr. The spectral response to the optimal stochastic perturbation reveals a strong peak at 35 yr, corresponding to the period of this oscillatory eigenmode. This study provides an upper bound of the meridional overturning response at multidecadal time scales to freshwater flux perturbation: for typical amplitudes of Great Salinity Anomalies, initial perturbations can alter the circulation by 12.25 Sv (1 Sv [ 10 6 m 3 s 21 ; i.e., 12.5% of the mean circulation) at most; stochastic perturbations with amplitudes typical of the interannual variability of the freshwater flux in midlatitudes induce a circulation variability with a standard deviation of 1 Sv (i.e., 5.5% of the mean circulation) at most.
In this paper, the combined assimilation of satellite observed sea level anomalies and in situ te... more In this paper, the combined assimilation of satellite observed sea level anomalies and in situ temperature data into a global ocean model, which is used to initialize a coupled ocean-atmosphere forecast system, is described. The altimeter data are first used to create synthetic temperature observations, which are then combined with the directly observed temperature profiles in an optimum interpolation scheme. In addition to temperature, salinity is corrected based on a preservation of the model's local temperature-salinity relationship. Coupled forecasts with a lead time of up to 6 months are initialized from the ocean analyses and the impact of the data assimilation on both the ocean analysis and the coupled forecasts is investigated. It is shown that forecasts of sea surface temperature anomalies in the Niño-3 area can be improved by initializing the coupled forecast model with the ocean analysis in which temperature and altimeter data are assimilated in combination. The results further imply that a good simulation of the salinity field is required to make optimum use of the altimeter data.
A simple coupled model is used in a zonally symmetric aquaplanet configuration to investigate the... more A simple coupled model is used in a zonally symmetric aquaplanet configuration to investigate the effect of ocean-atmosphere coupling on the Asian monsoon intraseasonal oscillation. The model consists of a linear atmospheric model of intermediate complexity based on quasi-equilibrium theory coupled to a simple, linear model of the upper ocean. This model has one unstable eigenmode with a period in the 30-60-day range and a structure similar to the observed northward-propagating intraseasonal oscillation in the Bay of Bengal/west Pacific sector.
In the present study, interannual fluctuations of the mixed layer depth (MLD) in the tropical Ind... more In the present study, interannual fluctuations of the mixed layer depth (MLD) in the tropical Indian Ocean are investigated from a long-term eddy permitting numerical simulation and a new observational dataset built from hydrographic in situ data including Argo data . Both datasets show similar interannual variability patterns in relation with known climate modes and reasonable phase agreement in key regions. Due to the scarcity of the observational dataset, we then largely rely on the model to describe the interannual MLD variations in more detail. MLD interannual variability is two to four times smaller than the seasonal cycle. A large fraction of MLD interannual variations is linked to large-scale climate modes, with the exception of coastal and subtropical regions where interannual signature of small-scale structures dominates. The Indian Ocean Dipole is responsible for most variations in the 10°N-10°S band, with positive phases being associated with a shallow MLD in the equatorial and south-eastern Indian Ocean and a deepening in the south-central Indian Ocean. The El Niño signature is rather weak, with moderate MLD shoaling in autumn in the eastern Arabian Sea. Stronger than usual monsoon jets are only associated with a very modest MLD deepening in the southern Arabian Sea in summer. Finally, positive Indian Ocean Subtropical Dipoles are associated with a MLD deepening between 15 and 30°S. Buoyancy fluxes generally appear to dominate MLD interannual variations except for IOD-induced signals in the south-central Indian Ocean in autumn, where wind stirring and Ekman pumping dominate.
This presentation describes results from the Air-Sea Interaction Profiler (ASIP), an autonomous p... more This presentation describes results from the Air-Sea Interaction Profiler (ASIP), an autonomous profiling instrument for upper ocean measurements. The measurements from ASIP are well suited to enhancing research on air-sea interfacial and near surface processes. Autonomous profiling is accomplished with a thruster, which submerges ASIP to a programmed depth. Once this depth is reached the positively buoyant instrument will ascend
Journal of Advances in Modeling Earth Systems, 2014
This paper presents the NOW regional coupled ocean-atmosphere model built from the NEMO ocean and... more This paper presents the NOW regional coupled ocean-atmosphere model built from the NEMO ocean and WRF atmospheric numerical models. This model is applied to the tropical Indian Ocean, with the oceanic and atmospheric components sharing a common 1 =4 horizontal grid. Long experiments are performed over the 1990-2009 period using the Betts-Miller-Janjic (BMJ) and Kain-Fritsch (KF) cumulus parameterizations. Both simulations produce a realistic distribution of seasonal rainfall and a realistic northward seasonal migration of monsoon rainfall over the Indian subcontinent. At subseasonal time scales, the model reasonably reproduces summer monsoon active and break phases, although with underestimated rainfall and surface wind signals. Its relatively high resolution results in realistic spatial and seasonal distributions of tropical cyclones, but it fails to reproduce the strongest observed cyclone categories. At interannual time scales, the model reproduces the observed variability associated with the Indian Ocean Dipole (IOD) and the delayed basin-wide warming/cooling induced by the El Niño Southern Oscillation (ENSO). The timing of IOD occurrence in the model generally matches that of the observed events, confirming the influence of ENSO on the IOD development (through the effect of lateral boundary conditions in our simulations). Although the KF and BMJ simulations share a lot in common, KF strongly overestimates rainfall at all time scales. KF also overestimates the number of simulated cyclones by a factor two, while simulating stronger events (up to 55 m s 21 ) compared to BMJ (up to 40 m s 21 ). These results could be related to an overly active cumulus parameterization in KF.
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Papers by Jérôme Vialard