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Beta and Advection Model (BAM)

The Beta and Advection Model (BAM) refers to a class of simple trajectory models that utilize vertically averaged horizontal winds from the GFS to compute TC trajectories. These trajectories include a correction term to account for the impact of the earth.s rotation. The BAM is based upon the concept of a simple relationship between storm intensity/depth and steering levels. Strong cyclones typically extend through the entire depth of the troposphere and are steered by deeper layer-average winds, while weaker cyclones are steered by shallower layer-average winds. The BAM is run in three versions corresponding to the different depths used in the trajectory calculation: BAM shallow (850-700 mb), BAM medium (850-400 mb), and BAM deep (850-200 mb), known as BAMS, BAMM and BAMD, respectively. The performance of the BAM is strongly dependent on the dynamical input from the GFS. A divergence of the three versions of the BAM indicates varying steering flow within the parent GFS model. Hence, spread among the three versions of the BAM also serves as a rough estimate of the vertical shear as well as the complexity and uncertainty in the track forecast.

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