SEMINAR: AOML Seminar - September 10, 2012 - 10:30 a.m. - Denis Volkov - “The Azores Current: Variability and Formation” and “On the Dynamics in the Lofoten Basin of the Norwegian Sea”

[Aoml.Receptionist <aoml.receptionist@noaa.gov>]

AOML Seminar

Date:           Monday, September 10, 2012

Time:          10:30 a.m. – refreshments at 10:15 a.m.

Location:   AOML First floor Conference Room

Speaker:    Denis Volkov

UCLA's Joint Institute for Regional Earth System Science  and Engineering

   Title:           “The Azores Current: Variability and Formation”

ABSTRACT:  The Azores Current (AzC) is a prominent eastward jet-like flow in the subtropical North Atlantic transporting about 10-12 Sv towards the Gulf of Cadiz. In my presentation, I will address the following major questions: i) how did the AzC vary during the 1993-2011 time interval, ii) what factors influence the variability of the AzC, and iii) what is the reason for the formation of the AzC? Space-borne observations of sea surface height have revealed a significant interannual variability of the AzC strength and eddy energy. Based on satellite altimetry, hydrography, and atmospheric reanalysis products, I will demonstrate that the interannual variability of the Azores Current eastward velocity and eddy energy may be driven by the adjustment of the ocean to the strength of westerly and trade winds, modulated by the North Atlantic Oscillation. Surface intensification (frontogenesis), which is mainly due to the wind‐driven meridional Ekman current convergence, is found significant, but not sufficient to explain the observed interannual variability of the AzC strength. Previous studies have suggested that the formation of the AzC may be the result of water mass transformation associated with the Mediterranean outflow in the Gulf of Cadiz. As the denser Mediterranean water descends down the continental slope, it entrains overlying North Atlantic Central Water. It has been hypothesized that the AzC then forms as part of the horizontal recirculating gyre generated through the b-plume mechanism. In the presentation, I will further explore this hypothesis by showing the results of several numerical experiments, based on a high-resolution general circulation model that includes the Mediterranean Sea and that realistically simulates the water mass exchange through the Strait of Gibraltar and the transport and variability of the AzC.

Title:          “On the Dynamics in the Lofoten Basin of the Norwegian Sea”  

ABSTRACT:  A sub-Arctic "hot spot" of intense mesoscale variability is observed in the Lofoten Basin (LB) - a topographic depression of about 3,250 m deep in the Norwegian Sea. It is the major heat reservoir for the Nordic seas, where large ocean-atmosphere interactions occur. Being a transit area for the warm and saline Atlantic Water (AW) on its way to the Arctic Ocean, it plays an important role in sustaining the Meridional Overturning Circulation for it is a region where the AW loses its heat to the atmosphere, mixes with surrounding water, and thus, undergoes transformation necessary for deep water formation. Satellite altimetry measurements reveal a cyclonic propagation of the mesoscale sea surface height anomalies in the LB. I will present evidences that these propagating signals are related to baroclinic topographic Rossby waves. Most of the observed waves have a wavelength of about 500 km and phase speeds ranging from 2 to 8 km/day. I will show that these waves are responsible for the localization and amplification of sea surface height variability in the LB. They can also play a significant role in local mixing and water mass transformation.