.. py:function:: average_ew(fs, area, increment)
Computes the zonal average for each field in ``fs`` for a set of latitude belts.
:param fs: input fieldset
:type fs: :class:`Fieldset`
:param list area: area as [N,W,S,E] to perform the averaging
:param number increment: increment in degrees defining the size of the latitude belts
:rtype: 1d-ndarray or 2d-ndarray
If ``fs`` only contains one field a 1d-ndarray is returned otherwise the result is a 2d-ndarray.
The averaging is performed for each field individually within the latitude belts defined by ``area`` and ``increment``. Each grid point value is weighted by the cosine of its latitude. Missing values are ignored. If a latitude belt contains no grid point values Nan is returned for that belt.
:Example:
.. code-block:: python
ave = mv.average_ew(fs, [60,-180,-60,180], 2.5)
Here we compute the averages over full latitude circles starting from 60N, stepping by 2.5 degrees until 60S. If ``fs`` contains only one field the output will be a 1d-ndarray of 49 E-W average values, from North to South. If ``fs`` contains n fields then the output will be an array of n 1d-arrays each containing 49 values. Each value in the result represents the average at latitude Lat based on those grid points whose latitude coordinate is between Lat-1.25 and Lat+1.25 (1.25 is 2.5/2), i.e. within a latitude belt with width of 2.5 degrees, centered around Lat.
.. note::
See also :func:`average_ns`.
.. mv-minigallery:: average_ew