Why minor ticks disappear on pylab subplots - python-2.7

Question

Begin Edit
After initial post I continued playing with my code. In my subplots I am making four plots of the same data set, with each subplot having a different time range. However, if I give each subplot the SAME time range then the minor ticks do not disappear. This may be why Deditos could not reproduce my issue.
That being said, if I manually create each subplot (with each having a different x-axis range), set the minor tick locations, THEN set each subplot's xrange I do not see the minor ticks disappear until I set ax3's (i.e. the last subplot) range.
It seems the issue is in having different x-axis ranges. Bizarre, I would think that by setting each axis' properties individually they would not all be tied together.
End Edit
I am creating one figure that has four sub-plots, all of which are time series. I have the xaxis major ticks spaced every four hours, and want minor ticks every hour. When I set the minor ticks for the first subplot (called ax1) the minor ticks appear, as they should. However, when I set the minor ticks in ax2 they show up in ax2, but the minor ticks in ax1 disappear. This repeats for ax3, and ax4. So, in the end I have only minor xaxis ticks in the fourth subplot. I had the same problem with the yaxis, but resolved this issue using yaxis.set_minor_locator(MultipleLocator(5)) for each axis (see below). However, MultipleLocator does not seem to work for time series data. Does anyone know how I can keep my minor xaxis ticks?
from pylab import *
from matplotlib.ticker import AutoMinorLocator, MultipleLocator
minor = AutoMinorLocator()
# Start plotting
fig = figure( figsize=(22,11) )
ax1 = fig.add_subplot(221) # 8-August 2011
ax2 = fig.add_subplot(222) # 9-August 2011
ax3 = fig.add_subplot(223) # 23-August 2011
ax4 = fig.add_subplot(224) # 24-August 2011
# This is repeated for ax2, ax3, and ax4, yielding a 2x2 grid of subplots.
# Plot 8-August 2011 data
ax1.plot(tpan.index,tpan.no2,'.-',markersize=10)
ax1.errorbar(tacam.index,tacam.no2,yerr=0.15,fmt='r.',markersize=12)
# Format plots
suptitle('Pandora/ACAM NO$_2$ Comparison', fontsize=22)
# Define xtick locations/string labels
xtickloc = [dt.datetime.combine(dates[0],dt.time())+dt.timedelta(hours=h) for h in range(0,25,4)]
xticklab = [dt.datetime.strftime(h,'%H:%M') for h in xtickloc]
ax1.set_xlabel('Hour of Day (UTC, EST+5)',fontsize=14)
ax1.set_ylabel('NO$_2$ Column Density (molec*cm$^{-2}$ E16)',fontsize=14)
ax1.xaxis.set_ticks(xtickloc)
ax1.yaxis.set_ticks(linspace(0,1.5,7))
ax1.xaxis.set_minor_locator(minor)
ax1.yaxis.set_minor_locator(MultipleLocator(5))
ax1.set_xticklabels(xticklab,fontsize=12,fontweight='bold')
ax1.set_yticklabels(linspace(0,1.5,7),fontsize=12,fontweight='bold')
ax1.axis( (dates[0],dates[0]+dt.timedelta(days=1),-0.05,1.5),fontsize=6,fontweight='bold')
ax1.tick_params(which='both',width=2,top='on')
ax1.tick_params(which='major',length=7)
ax1.tick_params(which='minor',length=4)
ax1.grid(linestyle='-',which='major',linewidth=1)
ax1.set_title('08-August 2011',fontsize=16)
ax1.legend( ('Pandora VCD','ACAM dSCD'),loc=2,ncol=2)

Answer 1

I was facing the same problem. I think what you need to do is:
ax1.xaxis.set_minor_locator(AutoMinorLocator())
instead of
ax1.xaxis.set_minor_locator(minor)
You are passing the same object to each of your axes. This object's contents are modified when you plot on ax4 based on the range on that subplot. Hope it helps.