Manuscript # 2012GL052920
Title: Is The North American Monsoon Self-Limiting?
Authors: Roop Saini^, Mathew Barlow# and Andrew Hoell+
^
Dept of Civil & Environmental Engineering, University of Connecticut, Storrs, CT
#
Dept of Environmental, Earth and Atmospheric Sciences, University of Massachusetts
Lowell, Lowell, MA
+
Geography Department, University of California Santa Barbara, Santa Barbara, CA
Table 1 Dates of onset of the Northwest Mexico monsoon for each year, based on the
daily precipitation index defined by Higgins et al. (1999). Note that 1951 and 1953 years
never met the onset criteria.
Figure 1 Comparison of the terms of the thermodynamic equation at 500hPa for 15-day
average before the onset (day -15 to day 1) and 15-day average after the onset (day 1 to
day +15): (A,D) the temperature advection term (red represents warm advection and blue
represents cold advection), (B,E) the vertical velocity term (blue represents rising motion
and red represents subsidence), and (C,F) the diabatic heating term (red represents
positive values and blue represents negative values). The contour interval is 0.43 K day-1
throughout.
Figure 2 Comparison of 18 strong and 18 weak advection monsoon years for the changes
in precipitation for 15-day average after the onset (day 1 to day +15) and the 15-day
average before the onset (day -15 to day 1) over northwest Mexico. The contour interval
is 0.25 mm day-1.
Figure 3 Comparison of 18 strong and 18 weak precipitation years for southwest U.S. for
the changes in the terms of the thermodynamic equation at 500hPa associated with the
onset: (A, D) the temperature advection term (red represents warm advection and blue
represents cold advection), (B, E) the vertical velocity term (blue represents rising motion
and red represents subsidence), and (C, F) the diabatic heating term (red represents
positive values and blue represents negative values). NCEP-NCAR reanalysis data is
used to calculate the thermodynamic variables. The contour interval is 0.22 K day-1
throughout.
Figure 4 Comparison of 18 strong and 18 weak precipitation years (shading) over SW
U.S. and 200hPa winds (vectors) for 15-day average after the onset (day 1 to day +15)
and the 15-day average before the onset (day -15 to day 1). The contour interval is 0.25
mm day-1 and a 10 m/s reference wind vector is given below the figure.