Julian day or days accumlation

North America

Allows further analysis…

A(day) = ( R(n) " R )

n=1 day

#

This is

‘Anomalous Accumulation’:

R

R

‘Onset’ (‘End’) is defined as day after which accumulation exceeds (is less than) climatology

Characteristics…

• ^local

• objective

• always defined

• ‘false’ onsets excluded

A Definition for Onset and End of the Rainy Season

Brant Liebmann and Dave Allured CIRES Climate Diagnostics Center

Note unusual equatorward progression of rainy season in South America….

Works in ‘problem’ areas...

South America

There are occasional ambiguities in some areas…

-100 -50 0 50 100 150 200 250 300

150 200 250 300

Examples of Anomalous Accumulation near Tucson (111W, 32N)

1969 1971 1983 1984 1989 1999

accumlation

Julian Day -100

-50 0 50 100 150 200 250 300

150 175 200 225 250 275 300 325 monsoon core (2 degrees of 29N, 110W)

accumlation

Julian Day 1954 1996 End Start

Length

(limits for 1954)

0 2 4 6 8 10 12 14 16 18

-20 -15 -10 -5 0 5 10 15 20

Northwest Amazon (1.3S, 67.5W)

daily precipitation (mm)

day relative to onset or end

Variance of annual total precipitation…

25 75 125 175 225 275

1965 1970 1975 1980 1985 1990 1995 2000 Near Tucson (111W, 32N) Wet season length has decreased....

onset end length

year

Julian day or days

100 150 200 250 300 350 400

1965 1970 1975 1980 1985 1990 1995 2000 But the June - October total

has increased slightly....

year

Jun - Oct total (mm)

2 2.5 3 3.5 4 4.5

1965 1970 1975 1980 1985 1990 1995 2000 Since the wet season rate has increased

year

mm/day