Part 3 - Front climatology

Prepared by Robin Noyelle.

The objectives of this part are the following:

  • compute warm and cold fronts over the 10 years period of the data

  • make a climatology of the fronts you found

Note that the more we go on the less you are guided. We expect you to become more independent with handling the data and knowing how to solve the problem by yourself. Please ask questions when you feel lost but still try to propose something to answer the questions we are asking !

Preparation

Now you should be familiar with this part and we let you do what you feel is necessary :)

Compute warm and cold fronts over the 10 year period of the data

Everything is in the title: you should make the previous computations that we did for one time step, but now for the whole data set. Once your files are computed, save them in the data folder using the to_netcdf function of xarray. Remember that xarray is a wrapper of numpy, do you really need to do a slow for loop over all dates of the dataset?

Climatology of fronts

What is usually called a ‘climatology’ in our field is some sort of average and/or frequency of an event. In our case, we would typically be interested by the proportion of time when there is a front at a certain grid point.

  1. Plot a world map of the mean frequency of warm and cold fronts over the whole year. What do you observe?

  2. We are also typically interested by how much the frequency of a certain event varies seasonally. Make a world map of the mean frequency of warm and cold fronts in the four seasons. What do you observe ? Can you propose a way to visualize in each season whether the frequency you found is higher or lower than the whole year frequency?

  3. With our procedure we identify a lot of tropical fronts which have a very different dynamics than mid-latitude fronts. Try to plot the yearly and seasonal climatologies of the frequency of cold and warm fronts in the Northern and Southern hemisphere with a map centered on the pole and ending up at 30 degrees (north or south depending on the hemisphere), as figure 5 in Schemm et al. (2015). What do you observe? Do you find the same orders of magnitude for the frequency as in this paper?

Bonus question: follow-up of the bonus question from the previous part, redo the same analysis as the one asked here by separating between cold fronts, warm fronts and stationary fronts.

References

Schemm, S., Rudeva, I., & Simmonds, I. (2015). Extratropical fronts in the lower troposphere–global perspectives obtained from two automated methods. Quarterly Journal of the Royal Meteorological Society, 141(690), 1686-1698.