202
P. Cipollini et al.
in which momentum and information are distributed across the oceans, begs for
further research. In light of this, Fyfe and Saenko (2007) modelled the alteration
in stratification of the ocean’s upper layers, based on the changes predicted by all
the IPCC emissions scenarios. Using only linear theory, the authors found that the
heating of the ocean’s upper layers would induce a wave speed-up that begins to
show at the lower latitudes by the end of the twentieth century, extending to the
higher latitudes as time progresses.
The model runs showed a 20–40% increase across all the model scenarios and in
particular a 35% speed increase for scenario A2 by the end of the twenty-first century (all compared to pre-industrial era speeds). These results reinforce the notion
that the expected changes in ocean properties will change planetary wave speeds,
decreasing the ocean’s response time to external forcing. This has the potential to
change ocean dynamics, such as the time-set of the ENSO, ocean-gyre circulation
and western boundary currents, thus impacting on climate. A proper understanding
of planetary wave speeds seems therefore to be fundamental to our knowledge of
the oceans/climate system and the way we model it.
The coexistence of multiple altimeters with different spatial and temporal sampling patterns (due to the different orbital configuration of the satellite platforms,
which results in different orbit inclinations and orbital repeat cycles) has prompted
for a merging of the data, based on optimal interpolation techniques (Le Traon et al.,
1998; Ducet et al., 2000) in order to increase the resolution of the SSH fields. This
merging has improved our view of the mesoscale, allowing a much better resolution
of those scales typical of oceanic eddies (for a review see Le Traon and Morrow,
2001). Chelton et al. (2007) have investigated the mesoscale variability of the global
ocean using the improved fields (namely, merged TOPEX/Poseidon and ERS-1 and
ERS-2 satellite datasets distributed by AVISO), finding that a significant fraction of
that variability is accounted for by eddies, mostly non-linear, with amplitudes of
5–25 cm and diameters of 100–200 km. This study and other recent studies on
eddies are reviewed by Fu (Chapter 9) in this same volume. Ongoing research is
attempting to decompose the westward propagating energy into spectral “macrocomponents” that can be unambiguously mapped into different processes, and its
early results confirm the co-existence of eddies and planetary waves over most of
the ocean, with linear waves larger within 20–30 ◦ of the equator and non-linear
eddies prevailing outside of that band (Matthew Thomas, Personal communication).
12.4 Current Research and Open Questions
Current research on westward propagating features is now focusing on a few questions opened by altimetric observations, alone or in combination with other satellite
datasets. In this section we review two classes of “open questions”: those that only
concerns the physics of the propagating features, and those that instead concern the
features’ impact on the biology.
P. Cipollini et al.
in which momentum and information are distributed across the oceans, begs for
further research. In light of this, Fyfe and Saenko (2007) modelled the alteration
in stratification of the ocean’s upper layers, based on the changes predicted by all
the IPCC emissions scenarios. Using only linear theory, the authors found that the
heating of the ocean’s upper layers would induce a wave speed-up that begins to
show at the lower latitudes by the end of the twentieth century, extending to the
higher latitudes as time progresses.
The model runs showed a 20–40% increase across all the model scenarios and in
particular a 35% speed increase for scenario A2 by the end of the twenty-first century (all compared to pre-industrial era speeds). These results reinforce the notion
that the expected changes in ocean properties will change planetary wave speeds,
decreasing the ocean’s response time to external forcing. This has the potential to
change ocean dynamics, such as the time-set of the ENSO, ocean-gyre circulation
and western boundary currents, thus impacting on climate. A proper understanding
of planetary wave speeds seems therefore to be fundamental to our knowledge of
the oceans/climate system and the way we model it.
The coexistence of multiple altimeters with different spatial and temporal sampling patterns (due to the different orbital configuration of the satellite platforms,
which results in different orbit inclinations and orbital repeat cycles) has prompted
for a merging of the data, based on optimal interpolation techniques (Le Traon et al.,
1998; Ducet et al., 2000) in order to increase the resolution of the SSH fields. This
merging has improved our view of the mesoscale, allowing a much better resolution
of those scales typical of oceanic eddies (for a review see Le Traon and Morrow,
2001). Chelton et al. (2007) have investigated the mesoscale variability of the global
ocean using the improved fields (namely, merged TOPEX/Poseidon and ERS-1 and
ERS-2 satellite datasets distributed by AVISO), finding that a significant fraction of
that variability is accounted for by eddies, mostly non-linear, with amplitudes of
5–25 cm and diameters of 100–200 km. This study and other recent studies on
eddies are reviewed by Fu (Chapter 9) in this same volume. Ongoing research is
attempting to decompose the westward propagating energy into spectral “macrocomponents” that can be unambiguously mapped into different processes, and its
early results confirm the co-existence of eddies and planetary waves over most of
the ocean, with linear waves larger within 20–30 ◦ of the equator and non-linear
eddies prevailing outside of that band (Matthew Thomas, Personal communication).
12.4 Current Research and Open Questions
Current research on westward propagating features is now focusing on a few questions opened by altimetric observations, alone or in combination with other satellite
datasets. In this section we review two classes of “open questions”: those that only
concerns the physics of the propagating features, and those that instead concern the
features’ impact on the biology.