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SUMMARY:The impact of hybrid oceanic data assimilation in a coupled model:
  A case study of a tropical cyclone - Tsz Yan Leung (Met Office)
DTSTART:20220923T133000Z
DTEND:20220923T135000Z
UID:TALK180299@talks.cam.ac.uk
DESCRIPTION:Tropical cyclones tend to result in distinctive spatial and te
 mporal characteristics in the upper ocean\, which suggests that traditiona
 l\, parametrisation-based background-error covariances in oceanic data ass
 imilation (DA) may not be suitable.&nbsp\; Using the case study of Cyclone
  Titli\, which affected the Bay of Bengal in October 2018\, we explore hyb
 rid methods that combine the traditional covariance modelling strategy use
 d in variational methods with flow-dependent estimates of the ocean's erro
 r covariance structures based on a short-range ensemble forecast.&nbsp\; T
 his hybrid approach is investigated in the UK Met Office's state-of-the-ar
 t system.&nbsp\; Single-observation experiments in the ocean reveal that t
 he hybrid approach is capable of producing analysis increments that are ti
 me-varying\, more anisotropic and vertically less uniform.&nbsp\; When the
  hybrid oceanic covariances are incorporated into a weakly coupled DA syst
 em\, the sea-surface temperature (SST) in the path of the cyclone is chang
 ed\, not only through the different specifications of background-error cov
 ariances used in the SST assimilation\, but also through the propagation o
 f subsurface temperature differences to the surface as a result of vertica
 l mixing associated with the cyclone's strong winds.&nbsp\; The coupling w
 ith the atmosphere then leads to a discrepancy in the cyclone's central pr
 essure\, which brings forth further SST differences due to the different r
 epresentations of the cyclone's emerging cold wake.\nTsz Yan Leung\, Amos 
 S. Lawless\, Nancy K. Nichols\, Daniel J. Lea\, Matthew J. Martin
LOCATION:No Room Required
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