An Historical Analysis of Transient Rain Bearing Systems in the NAME Domain:

An Historical Analysis of
Transient Rain Bearing Systems
in the NAME Domain:
The Impact of Inverted Troughs
on Monsoon Rainfall
Art Douglas and Phil Englehart
Creighton University
Research Objectives




1. To develop an historical climatology of
transient synoptic systems in northern Mexico.
2. To determine relationships between these
transient systems and fluctuations in summer
rainfall.
3. To relate variability in the frequency of
transient systems to large scale oceanic and
atmospheric anomalies.
4. To provide a benchmark for modeling studies
in order to determine model performance relative
to the prediction of these transient features and
their associated rainfall.
Transient Synoptic Features
Affecting Northern Mexico





1.
2.
3.
4.
5.
Tropical Cyclones (Published).
Inverted Troughs: Cold and Warm.
Cold Fronts.
Cutoff Lows.
Open Troughs.
LONG-TERM STATIONS
SEVEN SYNOPTIC REGIONS
1
1
1 1 11 1 1
11 1
2 2 5
2 22
5
22 2 5 5 5
5 5
55
33
5
33
5
33 5 5
33333
3
44 4
4
44
44
Data availability: 1950-2001
4
4
4
6
66
6
6
6
6
6
6
7 77
77
7
7
77
77
DAILY RAINFALL CLIMATOLOGY (1961-90)
(June 1- September 30)
CLASSIC MONSOON
9
JU
JL
AU
S
DAILY AVG. RAINFALL (mm)
8
7
6
5
SINALOA
4
SINALOA - SONORA
3
2
SONORA
1
SOUTHEAST ARIZONA
0
0 10 20 30 40 50 60 70 80 90 00 10 20 30
1 1 1 1
NORTHEAST & INTERIOR
DAILY AVG. RAINFALL (mm)
10
JU
JL
AU
S
9
8
7
6
5
4
TAMAULIPAS
3
DURANGO
2
CHIHUAHUA
1
0
0 10 20 30 40 50 60 70 80 90 00 10 20 30
1 1 1 1
TROPICAL CYCLONE TO TOTAL SEASONAL
RAINFALL (MEDIAN PERCENTAGE)
2
3
2 4
2
7
0
0
0
0
3 4
8
38
24
58
1
3
2 3
5
0
4 6
0 6
6
6 7
12
21
17
16
30
8
2
9 8
39
8
3
6
4
8
10
109
10
10
2
3 2
6
3
14
7
TC RAINFALL(mm) vs. LA NIÑA
by AMO PHASE
15
13
20
23
18
26
42
86
124
46
41
48
42
36
207
112
15
18
68
33
60
77
66
53
28
33
18
27
35
51
84
42
55
59
125
43
117
171
125
77
217
201 153
107
227
70
205
86
247
34
168
112
108
124
107
51
69
111
129
118 .4
182
152
98
95
153
209
125
175
91
145
101
115
156
134
168
96
201
144
POSITIVE AMO
NEGATIVE AMO
Transient Synoptic Features
Affecting Northern Mexico





1.
2.
3.
4.
5.
Tropical Cyclones (Published).
Inverted Troughs: Cold and Warm.
Cold Fronts.
Cutoff Lows.
Open Troughs.
RAOB Sites
NOAA NWS LIBRARY
Meridional Wind Time Section
8 July to 12 August 2005
Meridional Wind Time Section
July 1973
Days
Number of Inverted Trough-Days over the NAM Domain
1967 - 2001
80
72
64
56
48
40
32
24
16
8
0
1965 1970 1975 1980 1985 1990 1995 2000 2005
Comparison of Number of Synoptic Features
over the NAM Domain
CLIMO vs 2004
FRONTS
60
N o. of D ays
50
40
30
20
10
INVERTED
TROUGHS
CUT-OFF
LOWS
OPEN
TROUGHS
3.5
2.1
Average Daily Rainfall (mm)
Inverted Trough Days
4.4
3.5
vs.
5.2
3.0
Days with No Synoptic Feature
6.3
3.9
6.2
4.2
3.5
1.7
5.2
2.4
Increase in Daily Rainfall (%)
167
Inverted Trough Days
with respect to
125
173
Days with No Synoptic Feature
161
148
208
216
Inverted Troughs Contribution to Seasonal (June-Sept)
Rainfall (1967-2001)
Average Rainfall (mm)
Percent Contribution to Seasonal Total
51.9
22.3
72.3
15.7
116.2
25.6
121.0
20.5
137.9
21.7
93.1
27.4
101.1
19.9
RAINFALL Associated with INVERTED TROUGHS
as a function of TROUGH POSITION (i.e. Displacement
East (-) or West (+) of the Division Location in º Long.)
DURANGO
TAMAULIPAS/NUEVO LEON
9
9
8
8
8
7
7
7
6
6
6
5
4
Rainfall (mm)
9
Rainfall (mm)
Rainfall (mm)
SONORA/SINALOA
5
4
5
4
3
3
3
2
2
2
1
1
1
0
0
0
-4 -3 -2 -1
1
2
3
4
-4 -3 -2 -1
1
2
3
4
-4 -3 -2 -1
1
2
3
4
CONTRIBUTION OF INVERTED TROUGHS TO
SEASONAL TOTAL RAINFALL
2004/CLIMO
16.7
22.3
25.6
15.7
20.6
25.6
11.8
20.5
16.5
21.7
23.6
27.4
8.9
19.9
SONORA DAILY RAINFALL (mm) 2004 vs CLIMO
(11-pt Binomial Smoothing)
18
16
2004
Rainfall (mm)
14
12
CLIMO
10
8
6
4
2
0
0
14
28
42
56
70
JUNE 1 =1
84
98
112 126
Transient Synoptic Features
Affecting Northern Mexico





1.
2.
3.
4.
5.
Tropical Cyclones (Published).
Inverted Troughs: Cold and Warm.
Cold Fronts.
Cutoff Lows.
Open Troughs.
Days
Number of Frontal Days over the NAM Domain
1967 - 2001
60
54
48
42
36
30
24
18
12
6
0
1965 1970 1975 1980 1985 1990 1995 2000 2005
VIS 16Z October 7, 2005
Total Rainfall October 2-7, 2005
Comparison of Number of Synoptic Features
over the NAM Domain
CLIMO vs 2004
FRONTS
60
N o. of D ays
50
40
30
20
10
INVERTED
TROUGHS
CUT-OFF
LOWS
OPEN
TROUGHS
TAMAULIPAS/NUEVO LEON (DIVISION 7)
Percentage of Total Seasonal Rainfall Associated
with Fronts (< 350 km)
50
% seasonal total
40
30
20
2004 = 5.6
CLIMO = 5.9
10
0
1965 1970 1975 1980 1985 1990 1995 2000 2005
Comparison of Number of Synoptic Features
over the NAM Domain
CLIMO vs 2004
FRONTS
60
N o. of D ays
50
40
30
20
10
INVERTED
TROUGHS
CUT-OFF
LOWS
OPEN
TROUGHS
Number of CutOff Low-Days over the NAM Domain
1967-2001
60
50
Days
40
30
20
10
0
1965 1970 1975 1980 1985 1990 1995 2000 2005
Number of Open Trough-Days over the NAM Domain
1967 - 2001
50
Days
40
30
20
10
0
1965 1970 1975 1980 1985 1990 1995 2000 2005
Summary and Conclusions
1. A 35 year climatology of transient synoptic
features indicates that NAME 2004 was
characterized by:
a. Cold Front Days 200% of normal.
b. Inverted Trough Days 70% of normal.
c. Cutoff Low Days 90% of normal.
d. Open Trough Days 170% of normal.
2. Inverted troughs provide 20%-25% of the
summer rainfall received in NC and NE Mexico.
3. Rainfall with IV troughs peaks when the system
is overhead in NC Mexico. Rainfall peaks in
Western Mexico when the IV system is 3° to 4°
upstream: associated with MCS development
ahead of IV troughs (downslope, weak capping).
4. IV Rainfall in NE Mexico peaks when the
system is 4° upstream and this may be related to
disruption of the normal divergent trade system in
the western Gulf of Mexico
5. In NE Mexico cold fronts provide about 6% of
the normal summer rainfall (June to September).