Performance of operational systems with respect to water level forecasts in the Gulf of Finland

Abstract

This paper is devoted to the validation of water level forecasts in the Gulf of Finland. Daily forecasts produced by four setups of operational, three-dimensional Baltic Sea oceanographic models are analyzed using statistical means and are compared with water level observations at three Finnish stations located on the northern coast of the Gulf of Finland. The overall conclusion is that the operational systems were skillful in forecasting water level variations during the study period from November 1, 2003, to January 31, 2005. The factors causing differences between the water level forecasts of different models are discussed as well. An important task of operational sea level forecasting services is to provide accurate and early information about extreme water levels, both positive and negative surges. During the study period, two major winter storms occurred which caused coastal flooding in the region. According to our analysis, the operational models forecast the rise of water levels during these events rather successfully. Nowadays, operational forecasts can provide early warnings of extreme water levels at least 1 day in advance, which may be regarded as a minimum requirement for an operational forecasting system. The paper concludes that the models generally performed very well, with over 93% of the hourly water level forecasts found to be within the range of ±15 cm of the observed water levels, and with the timing of the water level peaks accurately predicted. Further discussion and studies dealing with the assessment of the skills of both operational meteorological and oceanographic forecasts, especially in connection with rare surge events, will be necessary. Skill assessment of operational oceanographic models would be relatively easy if acceptable error limits or a quality system was developed for the Baltic Sea operational models.

Operational sea level forecasting in Estonia

“…Low sub-range error is shifted to the positive side (low sea levels are predicted higher) and high sub-range to the negative side (high sea levels are predicted lower), which should be taken into account when interpreting RMSD values for corresponding sub-ranges. Such a distortion of low and high sea level forecasts was noted also for the northern coast of the Gulf of Finland [ 20 ].…”

“…The linear formulation was used to find the surface drag coefficient The value of bottom friction coefficient r was 0.0028. In the course of the model development, improved descriptions were introduced for vertical turbulence and drag coefficients on the surface and on the bottom [ 20,[25][26][27].…”

“…That model became a core of the family of operational models, run in addition to BSH also at the Swedish Meteorological and Hydrological Institute (SMHI) and Danish Meteorological Institute (DMI). An overview of different model versions and set-up features has been recently given in [ 20 ]. The model developments are coordinated by the HIROMB (High-Resolution Operational Model for the Baltic Sea) consortium.…”

Variability of currents over the southern slope of the Gulf of Finland

“…The model with a horizontal grid step of one nautical mile (1.852 km) is run at the Swedish Meteorological and Hydrological Institute (SMHI) and forced by the atmospheric model HIRLAM (SMHI), with a grid step of 22 km. In vertical, the model has a grid step of 4 m between the surface and 12 m, 6 m between 12 m and 30 m, 10 m between 30 m and 60 m and 15 m between 60 m and 90 m. In spite of poor vertical resolution, this model has proved to have a good prediction capability of the sea level (Gästgifvars et al, 2008) and has enabled quite reasonable forecasts of flow in different parts of the Gulf of Finland (Lagemaa et al, 2010). The model includes wind drag coefficient that depends on atmospheric stability (Elken et al, 2011) and the replacement of the Successive Corrections data assimilation scheme by the Optimal Interpolation method (Lagemaa et al, 2010).…”

BOOS/HIROMB-based marine forecasts in Estonia: Problems, experiences and challenges

“…We have noted earlier the +30 cm bias during the 2005 January storm (Section 3). In the Finnish coast of the Gulf of Finland, the sealevel prediction bias (zero drift) during October 2003 -September 2004 was from -9 cm in December to + 12 cm in August (Gästgifvars et al, 2004). …”