Exercise 7

Discussion

Because the Rossby radius is large in the tropics, mesoscale features tend to be transient with their evolution determined largely by the wind field. Even the evolution of many synoptic-scale disturbances is largely determined by the wind field. Thus, NWP models cannot make a good tropical forecast without good initial winds (first answer true, not fourth answer). In contrast, most mid-latitude systems that survive beyond around 12-18 hours have their dynamics governed largely by the mass field, so the models are in greatest need of temperature information to avoid a forecast bust (second answer). Wind in formation is more important on the mesoscale and has a shorter useful lifetime in the model (opposite of third answer), though in rapid evolution cases such as explosive "bomb" cyclogenesis, good winds and temperatures are both essential.

Thus, when making your forecast and evaluating a model forecast, you can estimate whether an observed or modeled feature is dynamically large or small in order to anticipate its influence and longevity and determine whether its governing characterisitics will be its wind or its temperature (fifth answer).

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		a) Wind observations assimilated into the model will have the biggest impact in the tropics.
		b) Assimilating temperature observations is most important in midlatitudes (for model forecasts beyond around 12-18 hours).
		c) Assimilating wind observations in most important in midlatitudes (for model forecasts beyond around 12-18 hours).
		d) Temperature observations assimilated into the model will have the biggest impact in the tropics.
		e) Estimating whether a feature is "large" or "small" compared to will allow your to infer what will happen to a feature when the forcing ends.