dim_avg averages the right most dimension of a variable. So, for TS(time,lat,lon), the lon dimension is averaged which results in a zonal average.
This example used dim_avg_Wrap which preserves meta data.
The zonal average plot is modified by using gsnZonalMeanXMinF, gsnZonalMeanXMaxF, and gsnZonalMeanYRefLine to set the minimum X-axis value, the maximum X-axis value, and the X-axis value where the reference line will be drawn.
gsnYAxisIrregular2Linear = True, transforms the irregular eta axis to a regular axis.
gsnYAxisIrregular2Log = True, Changes the y-axis to log scale when the original axis is irregular e.g. eta. If the y-axis is regular e.g. levels, then trYLog = True, should be used to set the y-axis to log scale.
cnInfoLabelOn = False, Turns off the contour information label.
The tickmark resources tmXBMode, tmXBValues, and tmXBLabels are set to explicitly label the X axis of a zonal means plot, and other resources are set to change the size and color of the X axis labels.