Joaquim Ballabrera-Poy

Coupled Ocean–Atmosphere Response to Seasonal Modulation of Ocean Color: Impact on Interannual Climate Simulations in the Tropical Pacific

The ability to use remotely sensed ocean color data to parameterize biogenic heating in a coupled ocean-atmosphere model is investigated. The model used is a hybrid coupled model recently developed at the Earth System Science Interdisciplinary Center (ESSIC) by coupling an ocean general circulation model with a statistical atmosphere model for wind stress anomalies. The impact of the seasonal cycle of water turbidity on the annual mean, seasonal cycle, and interannual variability of the coupled system is investigated using three simulations differing in the parameterization of the vertical attenuation of downwelling solar radiation: (i) a control simulation using a constant 17-m attenuation depth, (ii) a simulation with the spatially varying annual mean of the satellite-derived attenuation depth, and (iii) a simulation accounting for the seasonal cycle of the attenuation depth. The results indicate that a more realistic attenuation of solar radiation slightly reduces the cold bias of the model. While a realistic attenuation of solar radiation hardly affects the annual mean and the seasonal cycle due to anomaly coupling, it significantly affects the interannual variability, especially when the seasonal cycle of the attenuation depth is used. The seasonal cycle of the attenuation depth interacts with the low-frequency equatorial dynamics to enhance warm and cold anomalies, which are further amplified via positive air-sea feedbacks. These results also indicate that interannual variability of the attenuation depths is required to capture the asymmetric biological feedbacks during cold and warm ENSO events.

Relationship between zonal and meridional modes in the tropical Atlantic

The tropical Atlantic displays two main modes of variability; the meridional or dipole mode and the equatorial zonal mode. It was proposed recently, that these two modes are correlated and are both forced within the tropics by latitudinal displacements of the ITCZ. This modeling study shows that while the two modes are correlated for limited record lengths prior to and after 1976, the correlation falls apart when longer time-series from 1949 to 2000 are considered. The 1976 ‘climate shift’ also occurred in the tropical Atlantic seen as a thermocline shift similar to the Pacific, forced dynamically within the tropics. The first EOF of the simulated thermocline depth captures the inter-decadal mode with the 1976 shift. The first EOF of SST anomalies prior to (after) 1976 represents the meridional (zonal) mode, consistent with the previous finding that the relation between the eastern Pacific and Atlantic ITCZ is stronger in the 1980-90s.

Application of a Reduced-Order Kalman Filter to Initialize a Coupled Atmosphere–Ocean Model: Impact on the Prediction of El Niño

Abstract A reduced-order Kalman filter is used to assimilate observed fields of the surface wind stress, sea surface temperature, and sea level into the coupled ocean–atmosphere model of Zebiak and Cane. The method projects the Kalman filter equations onto a subspace defined by the eigenvalue decomposition of the error forecast matrix, allowing its application to high-dimensional systems. The Zebiak and Cane model couples a linear, reduced-gravity ocean model with a single, vertical-mode atmospheric model. The compatibility between the simplified physics of the model and each observed variable is studied separately and together. The results show the ability of the empirical orthogonal functions (EOFs) of the model to represent the simultaneous value of the wind stress, SST, and sea level, when the fields are limited to the latitude band 10°S–10°N, and when the number of EOFs is greater than the number of statistically significant modes. In this first application of the Kalman filter to a coupled ocean–atm...

Role of ocean biology-induced climate feedback in the modulation of El Nino-Southern Oscillation

Received 4 November 2008; revised 17 December 2008; accepted 29 December 2008; published 10 February 2009. (1 )E l Nino-Southern Oscillation (ENSO) properties can be modulated by many factors; most previous studies have focused on physical aspects of the climate system in the tropical Pacific. Ocean biology-induced feedback (OBF) onto physics and bio-climate coupling have been the subject of much recent interest, revealing striking model dependence and even conflicting results. Current satellite data are able to resolve the space-time structure of oceanic signals both in biology and physics, providing an opportunity for quantifying their relationships. Here we use the biological signature from satellite ocean color data to estimate interannual variability of the attenuation depth of solar radiation (Hp), a field linking ocean biology and physics. We then apply a singular value decomposition (SVD) analysis to interannual Hp and sea surface temperature (SST) anomaly fields to derive an empirical Hp model which is incorporated in a hybrid coupled ocean-atmosphere model of the tropical Pacific to represent the OBF. It is shown that the OBF can have significant effects on ENSO behaviors, including its amplitude, oscillation periods and seasonal phase locking. Citation: Zhang, R.-H., A. J. Busalacchi, X. Wang, J. Ballabrera-Poy, R. G. Murtugudde, E. C. Hackert, and D. Chen (2009), Role of ocean biology-induced climate feedback in the modulation of El Nino-Southern Oscillation, Geophys. Res. Lett., 36, L03608,

An Observing System Simulation Experiment for an Optimal Moored Instrument Array in the Tropical Indian Ocean

Abstract In this paper, a series of observing system simulation experiments (OSSEs) are used to study the design of a proposed array of instrumented moorings in the Indian Ocean (IO) outlined by the IO panel of the Climate Variability and Predictability (CLIVAR) Project. Fields of the Ocean Topography Experiment (TOPEX)/Poseidon (T/P) and Jason sea surface height (SSH) and sea surface temperature (SST) are subsampled to simulate dynamic height and SST data from the proposed array. Two different reduced-order versions of the Kalman filter are used to reconstruct the original fields from the simulated observations with the objective of determining the optimal deployment of moored platforms and to address the issue of redundancy and array simplification. The experiments indicate that, in terms of the reconstruction of SSH and SST, the location of the subjectively proposed array compareS favorably with the optimally defined one. The only significant difference between the proposed IO array and the optimal arr...

Decadal time‐series of SeaWiFS retrieved CDOM absorption and estimated CO2 photoproduction on the continental shelf of the eastern United States

[1] Published algorithms were employed to convert SeaWiFS images of normalized water-leaving-radiance to absorption images of CDOM (chromophoric dissolved organic matter). The best performing algorithm was employed to produce decadal time-series of CDOM monthly composites from 1998 through 2007. Deficits in CDOM absorption coefficient for surface waters across the shelf over the summer were then acquired relative to the uniformly mixed waters prior to and following stratification (spring and fall, respectively). Estimates were attained of the photochemical oxidation ofcarbontoCO2onandbeyondthe shelf of the Middle Atlantic Bight. Approximately 3–7 � 10 10 g C as CO2 were estimated to be produced via photooxidation of CDOM over the summertime, highlighting the significance of CDOM photochemistry and pointing out the importance of CO2 photoproduction at a global scale. In principle, this approach could be applied to global ocean color data. Citation: Del Vecchio, R., A. Subramaniam, S. Schollaert Uz, J. Ballabrera-Poy, C. W. Brown, and N. V. Blough (2009), Decadal time-series of SeaWiFS retrieved CDOM absorption and estimated CO2 photoproduction on the continental shelf of the eastern United States, Geophys. Res. Lett., 36, L02602,

Comparison between 1997 and 2002 El Nino events: Role of initial state versus forcing

n n Long time series of high quality ocean surface topography, sea surface temperature, subsurface temperature and salinity information allow a thorough comparison between two distinct El Nino events. The 1997 El Nino showed a strong ocean-atmosphere coupling which propagated from west to east. The weaker 2002 event developed later in the calendar year and showed strongest anomalies near the dateline. In this study, observational data of sea level and sea surface temperature from satellite, and subsurface temperature and salinity ( from all available sources including Argo) are used along with data assimilation to improve the initial state estimation of the ocean. Ocean model experiments are used to isolate differences between initial states of the system and forcing in the development of the two events. A statistical atmospheric model is utilized to highlight the atmospheric response to surface temperature anomalies. Different initial conditions for the month of November ( climatology, 1996 and 2001) are used to initiate model experiments forced by climatological European Centre for Medium-Range Weather Forecasts wind stress for the two El Nino periods (Nov 96 - Dec 97, Nov 01 - Dec 02). By differencing two experiments with the same forcing, but different initial conditions, the role of the ocean state at the start of the two events ( Nov 96 versus Nov 01) can be examined. These results show that both initial conditions are predisposed to induce a subsequent El Nino. However, for the first half of the 1997 event ( Nov 96 - Jun 97) the initial state of the ocean induces an eastward propagating wind field. For the 2002 event, the initial state served to limit the eastward propagation of the wind field by inducing destructive interference near the dateline. For the second half of the event (Jul 97 - Dec 97) the initial state contributed little. However, the role of initial conditions contributed nearly half the total signal for the peak of the 2002 event. Similarly, the role of the different forcing can be identified. These results show that for both events forcing played a very weak role over the first half of the year. ( In fact the statistical wind anomalies for these periods showed anomalous easterlies.) However, for the second half of the 1997 event the air/sea coupled forcing accounts for nearly all the temperature and wind anomalies. For the 2002 event, initial conditions and forcing contribute approximately equally to the temperature and resulting wind anomaly fields.

Microwave aperture synthesis radiometry: Paving the path for sea surface salinity measurement from space

This chapter summarises the main objectives and characteristics of the ESA’s SMOS mission and its remote sensing applications. The SMOS payload is MIRAS, a new type of instrument in Earth observation: the first two-dimensional aperture synthesis interferometric radiometer. It operates at L-band, has multi-angular and multi-look imaging capabilities, and can be operated in dual-polarisation or full-polarimetric modes. Due to its novelty, the principles of operation, imaging characteristics and its main performance parameters (spatial resolution and radiometric sensitivity and accuracy) are described, as well as the approach selected in the retrieval algorithms of sea surface salinity.

Decadal variability of shallow cells and equatorial sea surface temperature in a numerical model of the Atlantic

[1] The relative role of extraequatorial mechanisms modulating decadal sea surface temperature anomalies (SSTA) in the equatorial Atlantic is investigated using a suite of sensitivity experiments based on an ocean general circulation model. The model is forced by observed wind stress and/or computed heat flux from an associated advective atmospheric mixed layer model. In addition, the surface forcing is optionally applied on the equator or in off-equatorial regions. The long-term response of equatorial SST is dominated by local forcing. However, a weak but significant part of the response that is not in phase with the locally induced SST variability is caused by remote forcing. Subtropical cells (STCs) provide the oceanic bridging of the climate signals. The dynamical forcing leads to a spin-up and spin-down of the shallow cells, which, in the case of local forcing included, coincides with cold and warm SSTA. The local heat flux forcing reveals an overall damping tendency on the dynamical SST response. When excluding the local forcing, the isolation of the effect of the northern remote forcing from the one in the south appears to be essential in understanding the respective mechanisms at work. In the Northern Hemisphere, the spin-up and spin-down of the STC is highly correlated with the (lagging) SSTA, and the effect of off-equatorial heat flux forcing on SSTA is negligible. In the Southern Hemisphere, both momentum and heat fluxes in the subtropics lead to a significant SST response on the equator.

A new approach to improved SST anomaly simulations using altimeter data: Parameterizing entrainment temperature from sea level

n n Observed Topex/Poseidon/Jason-1 (T/P/J) altimeter sea level (SL) data are used to improve an empirical parameterization of the temperature of subsurface water entrained into the mixed layer (T-e). An inverse modeling method is first adopted to estimate T-e from a SST anomaly (SSTA) equation using observed SST and simulated upper ocean currents from an intermediate ocean model (IOM). An empirical relationship between anomalies of T-e (estimated) and SL (observed) from T/P/J altimeter is then constructed by utilizing a singular value decomposition (SVD) of their covariance. As compared with SSTA simulations using modeled SL data, the use of T/P/J SL data allows observed information about dynamic ocean adjustments to be built directly into the empirical T-e model being used to parameterize the thermocline effect on SSTAs. The improved T-e model leads to better SSA simulations in the tropical Pacific. Cross validation is made to examine the sensitivity of the SSTA simulations to the period chosen for training the T-e model. The proposed approach provides a new way to more effectively use T/P/J altimeter data in climate studies.