MRG Interactive Developments

Tropical Transition Thickness Diagnostics

The diagnostics presented here are the result of a latent class analysis run on one of the primary metrics to be used on objective TT classification, the lower-level thickness asymmetry. To compute this field, the maximum hemispheric 1000-700 hPa thickness asymmetry within 6deg of the centre of the incipient cyclone is evaluated at each time from T-36h to T-0h. An LCA algorithm is then used to group the derived time series' into classes with distinct evolution characteristics.

The LCA algorithm finds 5 robust groups in the data, as shown in the figure below.

The x-axis of this figure shows the time evolution of the thickness asymmetry field, and the y-axis shows its magnitude for the 5 groups identified by the LCA. The fraction of storms (591 storm total) that are members of each group are noted at the bottom of the plot. The trajectories for groups 1 and 5 are fit with quadratics, while groups 2, 3 and 4 are fit with linear curves.

Group Genesis Maps

As a preliminary investigation of the genesis location characteristics of each of the identified groups, a set of genesis maps (similar to those on the main page) have been produced. Note that the TT nomeclature ("Strong TT", "Weak TT", "Trough Interaction" and "Tropical Development") is used here only to indicate decreasing magnitudes of thickness asymmetry (i.e. we are not implying that all storms in the Strong TT group are, in fact, strong TT's, just that they have very large thickness asymmetry values). The Strong TT category includes the two strongest thickness asymmetry groups (4 and 5). The Weak TT, Trough Interaction, and Tropical Development categories comprise of group 3, 2 and 1 members, respectively.

Summary (All Storms)

This genesis plot shows the thickness asymmetry groupings for all storms in the dataset.

Strong TT (strong asymmetry groups 4,5)

This genesis plot shows the thickness asymmetry groupings for LCA-identified groups 4 and 5.

Weak TT (moderate asymmetry group 3)

This genesis plot shows the thickness asymmetry groupings for LCA-identified group 3.

Trough Interaction (weak asymmetry group 2)

This genesis plot shows the thickness asymmetry groupings for LCA-identified group 2.

Tropical Development (negligible asymmetry group 1)

This genesis plot shows the thickness asymmetry groupings for LCA-identified group 1.

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