Event and Seasonal Scale Variability of Surface Heat and Momentum Fluxes

EA : Event and Seasonal Scale Variability of Surface Heat and

Momentum Fluxes As part of the NSF-funded Ocean Observatories Initiative (OOI) Coastal and Global Scale Arrays, surface buoy meteorological measurements are made using the

Air-Sea Interaction Meteorology (ASIMET) package (Figure 20). These measurements are reported on in

Dever, E.P, J.P. Fram, C.M. Risien, R.A. Desiderio, C.E.

Wingard (2020), Event and Seasonal Scale Variability of

Surface Heat and Momentum Fluxes off Oregon and

Washington, Abstract [A144A-2411] presented at Ocean

Sciences Meeting 2020, San Diego, CA, 17-21 Feb.

Radiative and bulk surface fluxes calculated from these measurements are provided as OOI data products. Both the measurements and the estimated fluxes are available through the OOI Data Portal as are all the metadata required to produce these fluxes (raw data, calibration coefficients, data product specifications, data product algorithms etc.).

On the Endurance Array, ASIMET measurements are made at four locations over the Oregon and Washington shelf and slope. These locations lie within the northern

California Current Marine Ecosystem. Here upwelling favorable wind forcing and atmospheric conditions occur in spring and summer months with forcing in other months driven by passing low pressure systems. The timing of both the spring transition to upwelling and the fall transition to storm forcing varies from year to year as does the strength of individual events within each season.

Upwelling events are associated with strong net shortwave and latent heat fluxes. Storm events are associated with weak net shortwave fluxes and latent fluxes that vary in strength. Machine to machine (M2M) calls were used to read in hourly bulk surface fluxes from OOI Endurance Array moorings from their initial deployments in April 2015 through February 2020. OOI data product fluxes are calculated with TOGA-COARE and other community standar d algorithms . Monthly averages of OOI Endurance Array flux data compare well with one another. Both the Oregon and Washington shelves are subject to heating on an annually averaged basis. The Oregon Shelf mooring (Figure 21) is typical. Late fall and winter show net fluxes from the ocean to the atmosphere. All other months show heat flux into the ocean due to insolation.

RCA : One of the Longest Records for Tsunami Research in the Ocean

This study by Fine et al., [1] examines a 32-year record of high resolution bottom pressure recorder (BPR) measurements made by cabled instruments installed on Axial Seamount in 2014, and uncabled instruments at Axial, the Cleft Segment of the Juan de Fuca Ridge, DART buoys, and an IODP cored observatory (Hole 1026): most of the measurements in this study are from Axial (Figure 22). A total of 41 tsunamis were documented from 1986-2018 with all events associated with tsunamigenic earthquakes with magnitudes of 7.0 or greater. In contrast to coastal tide gauge observations, open ocean measurements by BPRs are advantageous because of the high signal-to-noise ratio. Based on this study, it is possible to forecast the effect of a tsunami originating from a source near a historical source, not only for Axial, but also for locations along the British Columbia-Washington- Oregon coast. These results allow a size-frequency model world-wide. The RCA cabled bottom pressure-tilt instruments, with 20 Hz sampling rates and with resolutions of 2 mm of seawater depth, provide especially high-resolution [1] Fine, I.V., Thomson, R.E., Chadwick, W.W., Jr., and Fox, C.G., (2020) Toward a measurements. universal frequency occurrence distribution for tsunamis: statistical analyses of a 32-year bottom pressure record at Axial Seamount. Geophysical Research Letter, https://doi.org/10.1029/2020GL087372.

CGSN: Heat Flux and Water Mass Formation in the

Southern Ocean A recent study (Tamsitt et al., 2020, doi: 10.1175/JCLI-D19-0653.1) compares surface heat fluxes from the OOI

Southern Ocean surface mooring and the Southern

Ocean Flux Station (SOFS) in the southeast Indian

Ocean. Wintertime surface heat loss is the primary driver for Subantarctic Mode Water (SAMW) formation, but there are few direct observations of heat fluxes.

These two moorings provide the first concurrent, multiyear time series of air–sea fluxes from two key

SAMW formation regions. It is found that both sites are dominated by transient heat loss events in austral winter, and those events tend to be stronger at the

SOFS site than at OOI. There is large interannual variability in the cumulative ocean heat loss at both locations.

The study also highlights the importance of sustained observations. It is found that heat loss events at the OOI site are associated with a single atmospheric regime (cold air from the south), whereas the SOFS site is impacted by two regimes. This differs from early results, using just the first year of observations from SOFS, which found only one atmospheric regime, analogous to that at the OOI site, dominated heat loss. It is suggested that the proximity of the SOFS site to the

Australian continent leads to frequent strong latent heat loss events when drier air is advected over the region from the northwest, whereas at the OOI site air from the northwest is warm and moist, rarely leading to ocean heat loss. This result has implications for the role of episodic heat loss and SAMW formation on longer time