The Bjerknes Centre is a collaboration on climate research, between the University of Bergen, NORCE, the Institute of Marine Research, Nansen Environmental and Remote Sensing Centre.

Seminar: Atlantic water supply toward the 79N Glacier in Northeast Greenland

Hisashi Nakamura from RCAST, University of Tokyo will give a seminar talk on 5 December.

Portrett Nakamura
Hisashi Nakamura

Short biography:
Currently, Professor of RCAST (Research Center for Advanced Science and Technology), University of Tokyo;
Ph.D. from University of Washington, Postdoc a GFDL, Princeton, Faculty member at Graduate School of Science, University of Tokyo;
Climate dynamics, ocean-atmosphere interaction, extreme weather conditions and climate change;
Collaboration with GFI scientists through NORPAN/UNPACC and Belmont Forum InterDec;
Chair of JMA Advisory Board on Extreme Climate Events, member of JMA reanalysis project, lead PI of "Hotspot project".

In time-mean fields, surface wind convergence and divergence are locally enhanced along the warm western boundary currents and to their poleward across SST fronts, respectively. This particular pattern has been interpreted as a manifestation of local boundary-layer response to frontal SST gradient via “hydrostatic effect” and/or “vertical mixing effect”. The surface convergence and divergence coincide with local enhancement and reduction, respectively, of upward motion, cloudiness, and precipitation. Recent studies argue, however, that recurrent development of synoptic-scale disturbances, which accompany extreme convergence and divergence, can be essential in shaping this time-mean atmospheric structure. It is still an open question as to the relative contributions from these potential processes to the time-mean pattern, which is investigated in this study with main focus on the wintertime the Kuroshio Extension (KE) and Oyashio fronts. Comparison is made between two additional products of the Japanese atmospheric reanalysis JRA-55 family, which use 25km and 100km resolution SST for lower boundary condition for the same data assimilation system. In the product with higher-resolution SST, moderately strong convergence tends to occur frequently even on daily scales right over the KE and moderate divergence slightly to the north, which are not directly related to atmospheric disturbances. Cyclonic disturbances give rise to enhanced convergence even to the north of the KE. Comparison of the two products suggests that not only the extreme convergence or divergence associated with synoptic-scale disturbances but also the moderate but more persistent contributions from the frontal-scale SST pattern can be important in shaping the time-mean meso-scale surface wind pattern and associated distributions of cloud and precipitation.

Arranged date for the seminar talk: Dec 05, 2018