Prioritize...
Once you have completed this section, you should know the key strengths and weaknesses of the Hovmöller diagram and describe what it can and cannot provide.
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As with all techniques we have learned, there are strengths and weaknesses to the Hovmöller diagram. In addition, sometimes we infer too much from the diagram. What can a Hovmöller diagram really provide to an analysis? Or more importantly, what can it not?
Strengths
Let’s start with the strengths. Hovmöller diagrams allow us to display A LOT of data, both spatially and temporally. Hovmöller diagrams allow us to assess the movement and evolution of spatial patterns in a variable over time. We can really start to look at the evolution of a meteorological event without watching a movie! In addition, the diagram highlights key places and times (as well as time and space scales) to examine in more detail. We saw a great ENSO example that highlighted strong events, pinpointing specific years we should examine in more detail. We can use the Hovmöller diagram as kind of a stepping stone…let it lead us. In short, the Hovmöller diagram is a fantastic exploratory tool. I would highly recommend using this sort of plot if you are studying anything with respect to the evolution of a variable or looking at a lot of data.
Weaknesses
Although the Hovmöller diagram may seem like a great tool, we must know its limitations. To start with, in most cases we will need to average over some dimension (e.g., latitude). When we average over a dimension, we lose the variability and characteristics of that variable with respect to that dimension (think back to the temperature example and averaging over the globe versus a hemisphere). This is why we need to carefully select the appropriate averaging technique and averaging domain. In addition, selecting the appropriate axes to display can be difficult. Although Hovmöller diagrams can provide quantifiable values for phase speed and group velocity, follow-up techniques may need to be added. In short, although the Hovmöller diagram is a great exploratory tool…that’s all it is…it is not the solution to a problem, but a step in the process.