Seasonal variability in the semidiurnal internal tide – a comparison between sea surface height and energetics
Year: 2024
Type: article
Abstract: . We investigate the seasonal variability of the semidiurnal internal tide steric sea surface height (SSSH) and energetics using 8-km global Hybrid Coordinate Ocean Model (HYCOM) simulations with realistic forcing and satellite altimeter data. In numerous previous studies, SSSH has been used to explore the seasonal changes in internal tides. For the first time, we compare the seasonal variability of the semidiurnal internal tide SSSH with the seasonal variability of the semidiurnal baroclinic energetics. We explore the seasonal trends in SSSH variance, barotropic to baroclinic conversion rate, kinetic energy, available potential energy, and pressure flux for the semidiurnal internal tides. We find that the seasonal cycle of monthly semidiurnal SSSH variance in the Northern Hemisphere is out of phase with the Southern Hemisphere. This north-south phase difference and its timing are in agreement with altimetry. The amplitudes of the seasonal variability in SSSH variance are about 10–15 % of their annual-mean values when zonally averaged. The normalized amplitude of the seasonal variability is higher for the SSSH variance than for the energetics. The largest seasonal variability is observed in Georges Bank and the Arabian Sea, where the seasonal trends of monthly SSSH variance and energetics are in phase. However, outside these hotspots, the seasonal variability in semidiurnal energetics is out of phase with semidiurnal SSSH variance and a clear phase difference between the Northern and Southern Hemispheres is lacking. While the seasonal variability in semidiurnal energy is driven by seasonal changes in barotropic to baroclinic conversion, semidiurnal SSSH variance is also modulated by seasonal changes in stratification. Surface intensified stratification at the end of summer enhances the surface perturbation pressures, which enhance the SSSH amplitudes.
Source: Ocean science
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,412
Awards: G10735966, G1266583311, G4153834542, G4720003262, G7540567840, WE PROPOSE TO INVESTIGATE THE GLOBAL INTERNAL TIDE-DRIVEN OCEAN MIXING BY COMBINING TWO COMPLEMENTARY TECHNIQUES: SATELLITE ALTIMETRY AND HYBRID COORDINATE OCEAN MODEL (HYCOM) SIMULATIONS. THE RESULTS WILL BE COMPARED WITH FIELD MEASUREMENTS MADE BY SHIPBOARD MICROSTRUCTURE AND CTD INSTRUMENTS. INTERNAL TIDES PROVIDE ABOUT HALF OF THE REQUIRED POWER FOR DIAPYCNAL MIXING IN THE OCEAN INTERIOR AND THUS PLAY AN IMPORTANT ROLE IN MODULATING THE GLOBAL OCEAN CIRCULATION AND CLIMATE. DESPITE DECADES OF FIELD MEASUREMENTS OCEAN MIXING REMAINS A CHALLENGING PROBLEM IN PHYSICAL OCEANOGRAPHY. WE HAVE CONSTRUCTED GLOBAL INTERNAL TIDE MAPS USING MULTI-YEAR MULTI-SATELLITE ALTIMETER DATA AND A NOVEL PLANE-WAVE FIT METHOD. LONG-RANGE INTERNAL TIDES ARE OBSERVED TO PROPAGATE OVER THOUSANDS OF KM FROM ENERGETIC GENERATION SITES IDENTIFIED BY EGBERT AND RAY (2000 2001). HYCOM IS A GLOBAL HIGH-RESOLUTION NUMERICAL MODEL WITH BOTH TIDAL AND ATMOSPHERIC FORCING AND WILL BE USED TO ESTIMATE THE INCOHERENT INTERNAL TIDES MISSED BY SATELLITE ALTIMETRY. BY COMBINING THESE TWO TECHNIQUES WE ARE ABLE TO MAP INTERNAL TIDE DISSIPATION FROM SPACE BY ADDRESSING THESE THREE MAJOR CHALLENGES: (1) INCOHERENT INTERNAL TIDES (2) INTERFERENCE OF MULTIPLE INTERNAL TIDAL WAVES AND (3) TEMPORAL VARIABILITY. WE HAVE FOUR SPECIFIC RESEARCH OBJECTIVES. (1) WE WILL COMPUTE THE ENERGY AND FLUX OF GLOBAL OPEN-OCEAN INTERNAL TIDES FROM SATELLITE ALTIMETRY AND HYCOM. OUR CALCULATIONS WILL INCLUDE THE FOUR LARGEST TIDAL CONSTITUENTS (M2 S2 O1 AND K1) AND THE TWO LOWEST BAROCLINIC MODES. (2) WE WILL QUANTIFY HOW MUCH INTERNAL TIDAL ENERGY REACHES AND LEAVES THE COASTAL REGIONS. (3) WE WILL QUANTIFY WHERE INTERNAL TIDES DISSIPATE IN THE GLOBAL OCEAN USING THE GLOBAL MAPS OF INTERNAL TIDE ENERGY FLUXES FROM SATELLITE ALTIMETRY AND HYCOM. (4) WE WILL INVESTIGATE THE SEASONALITY OF INTERNAL TIDES AND DISSIPATION. THIS PROPOSAL RESPONDS TO THE SOLICITATION OF THE NASA PO PROGRAM TO EXPAND OUR SPATIAL AND TEMPORAL ESTIMATES OF OCEAN MIXING. THE COMBINATION OF SATELLITE ALTIMETRY AND HYCOM OFFERS A NOVEL APPROACH TO TRACK LONG-RANGE INTERNAL TIDES FROM SPACE COMPLEMENTING PREVIOUS EFFORTS BY FIELD MEASUREMENTS. THIS PROPOSAL WILL IMPROVE OUR UNDERSTANDING OF THE SPATIAL AND TEMPORAL VARIATIONS OF INTERNAL TIDE AND OCEAN MIXING. IT WILL LEAD TO IMPROVED GLOBAL INTERNAL TIDE MODELS THAT ARE MUCH NEEDED BY NASA S NEXTGENERATION ALTIMETER SWOT. THE NEW KNOWLEDGE OF INTERNAL TIDES AND MIXING IS USEFUL TO THE NASA-SUPPORTED PROJECT ECCO2 WHICH IS INCORPORATING THE TIDE AND INTERNAL TIDE COMPONENTS., G8876996369
OpenAlex ID: W4402879725