MET/MODE IVT Verification

MODE, the Method for Object-Based Diagnostic Evaluation, provides an object-based verification for comparing gridded forecasts to gridded observations. It has most commonly been applied to precipitation fields and radar reflectivity, but here it is applied to integrated water vapor transport (IVT). IVT objects serve as a simplified approximation to an Atmospheric River (AR) detection tool. While the majority of IVT objects will be ARs, and the majority of ARs will be IVT objects, there may be some exceptions.
The maps show IVT objects that have an aspect ratio greater than 2 at a given threshold (250, 500, or 750 kg m-1 s-1). The IVT objects used for the statistics are further restricted by requiring the object to be longer than approximately 550 km, have a centroid latitude north of 20oN and east of 155oW, and have an axis angle of less than 100o. If there is more than one such IVT object, the statistics will be performed on the larger one. For more information on MODE click here.

Click here to view MODE verification applied to precipitation.

Valid Date

Model

Lead Time

Threshold

Forecasted

Object Verification

Model Analysis

MODE Overview

MODE, the Method for Object-Based Diagnostic Evaluation, provides an object-based verification for comparing gridded forecasts to gridded observations. MODE may be used in a generalized way to compare data from which objects may be well defined. It has most commonly been applied to precipitation fields and radar reflectivity. The steps performed in MODE consist of:

  • Define objects in the forecast and observation fields based on user-defined parameters.
  • Compute attributes for each of those objects: such as area, centroid, axis angle, and intensity.
  • For each forecast/observation object pair, compute differences between their attributes: such as area ratio, centroid distance, angle difference, and intensity ratio.
  • Use fuzzy logic to compute a total interest value for each forecast/observation object pair based on user-defined weights.
  • Based on the computed interest values, match objects across fields and merge objects within the same field.
  • Write output statistics summarizing the characteristics of the single objects, the pairs of objects, and the matched/merged objects.
  • MODE may be configured to use a few different sets of logic with which to perform matching and merging.

It is not uncommon for the domain of the model to cut short what would have been an IVT object, making it less likely that objects near the domain boundary will be identified. A curved IVT object is also less likely to be identified, since the computation of the aspect ratio includes the area in the middle of the curve.