Jacqueline Boutin, with Audrey Hasson, sent me this contribution, as part of our series of blog stories, to illustrate each day using a new case example, how it reveals, with unprecedented details, the influence of large scale climate events, like ENSO, Indian Ocean Dipole … on the two key hydrological cycle variables. Actually,the 2010-2017 SMOS measurements time series has allowed an unprecedented and unique monitoring of Sea Surface Salinity (SSS) and Soil Moisture (SM) and Cryosphere using L-band radiometry. here is one example!
The signature of ENSO on equatorial and extra-equatorial SSS in the Pacific Ocean
A. Hasson, J. Boutin and S. Marchand (LOCEAN, Paris)
Nearly 8 years of Sea Surface Salinity retrieved from the SMOS mission has enabled the observation of inter-annual variations associated with the El Niño Southern Oscillation. SMOS was launched just in time for a great two-year long La Niña event from mid 2010 to early 2012. Followed in 2014 a small El Niño event that prepared the Pacific Ocean for a large event from mid 2015 to mid 2016.
1- The equatorial SSS variability:
In the Western Pacific Ocean, a large body of fresh waters called the fresh-pool swings along the equator together with the El Niño Southern Oscillation as observed from in situ observations. SMOS measurements enables the much more precise description of the fresh-pool displacement and its previously unknown extension. In 2011, the equatorial western Pacific fresh pool retracts all the way to the western edge of the Pacific Ocean whereas in 2015 the fresh waters extend well east of the dateline.
Caption: 2010-2017 longitude-time plot of SMOS SSS averaged between 2ºS and 2ºN. The NINO3.4 index is displayed on top, centered on the dateline, blue during La Niña and red during El Niño https://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Data/nino34.long.anom.data. (SMOS CATDS CPDC L3Q products)
To know more about associated work:
A. Hasson, M. Puy, J. Boutin and E. Guilyardi; Northward Propagation across the Tropical North Pacific Ocean Revealed by Surface Salinity: How El Niño Anomalies Reach Hawaii?, submitted to JGR-Oceans
Boutin, J., J.L. Vergely, S. Marchand, F. D’Amico, A. Hasson, N. Kolodziejczyk, N. Reul, G. Reverdin (2017), Revised mitigation of systematic errors in SMOS sea surface salinity: a Bayesian approach, Remote Sensing of Environment, in revision.
2- The eastern Pacific fresh-pool:
Heavy rain from the Inter-tropical Pacific Convergence Zone is associated with a large area of low surface salinity in the eastern Pacific Ocean. In this very under sampled region of the ocean, SMOS gives us great insight in the ocean variability.
Since launch, an extension of the eastern Pacific freshwaters is observed as shown around 18ºN. Fresh waters are trapped east of 110ºW during the 2011 La Niña and extend to the dateline following the 2015 El Niño.
Caption: 2010-2017 longitude-time plot of SMOS SSS averaged between 16º and 20ºN. The NINO3.4 index is displayed on top, centred on the dateline, blue during La Niña and red during El Niño https://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Data/nino34.long.anom.data. (SMOS CATDS CPDC L3Q products)
To know more about associated work:
A. Hasson, M. Puy, J. Boutin and E. Guilyardi; Northward Propagation across the Tropical North Pacific Ocean Revealed by Surface Salinity: How El Niño Anomalies Reach Hawaii?, submitted to JGR-Oceans
Boutin, J., J.L. Vergely, S. Marchand, F. D’Amico, A. Hasson, N. Kolodziejczyk, N. Reul, G. Reverdin (2017), Revised mitigation of systematic errors in SMOS sea surface salinity: a Bayesian approach, Remote Sensing of Environment, in revision.
Guimbard S., N. Reul, B. Chapron, M. Umbert and C. Maes, 2017. Seasonal and interannual variability of the eastern tropical Pacific fresh pool, J. Geophys. Res. Oceans, doi: 10.1002/2016JC012130.
Alory, G., C. Maes, T. Delcroix, N. Reul, and S. Illig, 2012. Seasonal dynamics of sea surface salinity off Panama: the far eastern Pacific fresh pool. J. Geophys. Res., 117, C04028, doi:10.1029/2011JC007802.
3- The extra-equatorial anomalies
The unprecedented spatial and temporal coverage of the SMOS mission reveals poleward pathways of equatorial SSS anomalies as shown for the 2011 La Niña (Hasson et al. 2014) and for the 2014-2015 El Niño events (Hasson et al. 2017 submitted). Anomalies created at the equator by the displacement of the western Pacific fresh-pool and off the equator are exported poleward by the Ekman drift in a complex system of tropical currents.
Caption: 2010-2017 latitude-time plot of SMOS SSS anomalies produced by the CEC-LOCEAN averaged between 150º and 170ºW. The NINO3.4 index is displayed on top, centered on the equator, blue during La Niña and red during El Niño https://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Data/nino34.long.anom.data. (SMOS CATDS CPDC L3Q products)
To know more about associated work:
A. Hasson, M. Puy, J. Boutin and E. Guilyardi; Northward Propagation across the Tropical North Pacific Ocean Revealed by Surface Salinity: How El Niño Anomalies Reach Hawaii?, submitted to JGR-Oceans
A. Hasson, T. Delcroix, J. Boutin, R. Dussin, and J. Ballabrera-Poy (2014); Analyzing the 2010–2011 La Niña signature in the tropical Pacific sea surface salinity using in situ data, SMOS observations, and a numerical simulation, Journal of Geophysical Research: Oceans, 119(6), 3855-3867, doi:10.1002/2013JC009388.
Boutin, J., J.L. Vergely, S. Marchand, F. D’Amico, A. Hasson, N. Kolodziejczyk, N. Reul, G. Reverdin (2017), Revised mitigation of systematic errors in SMOS sea surface salinity: a Bayesian approach, Remote Sensing of Environment, in revision.