Ocean Dynamics
4) Springer
packages forming the regional monitoring and forecasting
centers for the Northwest Shelf (NWS) and the Baltic Sea
(BAL) which have been transformed to parts of CMEMS in
May 2015. The nominal forecast products for the two regions,
namely, FOAMAMM for NWS and DMI HBM for BAL
(see Table 1), are implemented in the MME. One goal in both
MyOcean work packages was to provide additional uncertainty
information on the nominal products. In addition, the MME
is now established as an independent service, taking advantage
of the various existing operational ocean forecasting
models, and benefitting the participating agencies and institutes.
This service is basically a supplement to validation and
provides a comparison of the contributing forecasts in order to
reveal the degree of agreement and deviation for different
parameters. The comparison is done on a daily basis to keep
track of the actual variations and to detect potential problems
in individual model systems. Based on the daily and long-term
results, the model systems can be improved and further
developed.
To enhance the sustainability and user uptake of the MME,
the development is done in close cooperation with the communities
of the Baltic Operational Oceanographic System
(BOOS, www.boos.org, accessed 24 October 2014) and the
Northwest European Shelf Operational Oceanographic
System (NOOS, www.noos.ee, accessed 24 October 2014).
These two communities are regional services integrated in
the European Global Ocean Observing System
(EuroGOOS). Both systems focus on the provision and
improvement of high-quality operational marine data.
This study is carried out for the North Sea and the Baltic
Sea which are connected by a Transition Area, the Skagerrak
and Kattegat. The Baltic Sea is characterized by brackish
waters with a surface salinity around 20 in the south
decreasing towards the north and east (about 2 in the
Bothnian Sea and the eastern Gulf of Finland). During
winter months, the northern parts of the Baltic Sea are
regularly covered by sea ice. The surface salinity is influenced
by freshwater inflow from rivers and melting sea ice
in spring (Feistel et al. 2008; Lepparanta and Myrberg
2009). The exchange of water masses between the North
Sea and Baltic Sea is characterized by high-saline water
entering the Baltic Sea via the Great Belt, the Little Belt,
and the Oresund by near-bottom currents. Low-saline surface
water is flowing out of the Baltic Sea. Sea surface
currents are mainly induced by wind and density gradients,
as well as by differences of water level. The dominant
feature of currents in the North Sea is the tidal motion
(Otto et al. 1990). The residual circulation is characterized
by a major inflow from the North Atlantic and the English
Channel and a major outflow from the Baltic Sea as the
Norwegian Costal Current. The surface salinity averages
between 34 and 35 in the central North Sea. There are
freshwater inflows from rivers, such as Rhine and Elbe,
and from the Baltic Sea affecting the surface salinity. The
surface temperature has a strong annual cycle in both
regions.
The MME systems of the North Sea and Baltic Sea as well
as the contributing models are presented in Sect. 2. Ensemble
statistics of the MME are explained and some examples are
displayed in Sect. 3. The uncertainty estimates between the
products are based on spatio-temporal statistics of the data
collected. As a result, regions with high and low uncertainties
as well as seasonal patterns can be identified. A comparison to
satellite data is presented. Results of the spatio-temporal statistics
are shown in Sect. 4 and a summary is given in Sect. 5.
2 MME system
2.1 Overview of contributing models
Thirteen different operational ocean forecasting models covering
either the North Sea or the Baltic Sea or both regions
contribute to the MME. Details on model area, boundary conditions,
and forcing are listed in Table 1. A brief overview of
each system is provided below. It should be noted, however,
that the forecasts are not frilly independent of each other since
most of the models covering the Baltic Sea are based on the
same kernel of model code (CMOD) and are therefore related
to a certain degree (Berg and Poulsen 2012). Furthermore,
some models are using the same forcing and boundary conditions.
Accordingly, it could be expected that the statistical
evaluation might be influenced by this dependency.
CMOD and HBM at BSH The Federal Maritime and Hydrographic
Agency (BSH) runs two forecast models with dynamical
vertical coordinates covering the North and Baltic Sea: the
operational Circulation Model CMOD (Dick et al. 2001; Dick
and Kleine 2008) and the pre-operational HIROMB-BOOS
Model, HBM (Berg and Poulsen 2012). Both model setups
consist of a coarse grid with a horizontal resolution of 3 nautical
miles (NM) and a maximum of 35 vertical layers, and a
two-way nested fine grid with a horizontal resolution of
0.5 NM and a maximum of 25 vertical layers covering the
inner German Bight and Western Baltic. While CMOD uses
a simple algebraic turbulence model (Kleine 1994), HBM
runs with a k-omega turbulence model (Berg 2012).
DKSS2013 and HBM at DMI The Danish Meteorological
Institute (DMI) runs the storm surge model DKSS2013 and
HBM as the nominal MyOcean product, which both cover the
North Sea and Baltic Sea (Berg and Poulsen 2012). The model
runs on a two-way nested rectangular grid. The horizontal
resolution of DKSS2013 is 3 NM in the main domain,
1 NM in the Wadden Sea, and 0.5 NM in the Transition Area.
The model setup consists of vertical z-coordinates with a
