Analysis on the Origins of
East Pacific Easterly Waves
Ernesto Findlay
Department of Earth and Atmospheric Sciences, State University of New York, Albany New
York
Adam Rydbeck and Eric Maloney
Department of Atmospheric Science, Colorado State University, Fort Collins Colorado.
46TH Annual AGU Fall Meeting
San Francisco, CA
Monday, 9 December 2014
Motivation
 To better understand the
origins and tracks of
easterly waves in the east
Pacific
 Over the last 15 years,
70% of tropical cyclones in
the east Pacific developed
from African easterly
waves (NHC)
What is an easterly wave?
 Inverted v-shaped wind pattern
 Inverted trough of low pressure
Easterly wave
climatology
a. Track density
b. Genesis density
c. Lysis density
Serra et al. (2010)
Data
TRMM precipitation dataset (0.5° resolution) from
1999–2009
NCEP/NCAR reanalysis zonal and meridional winds
(2.5°resolution) from 1998–2012
WRF simulation (54 km grid spacing) for August 2005
case study
Climatology
Significant background cyclonic vorticity
Ample background precipitation favorable for easterly wave
growth, with maximum in bight of Panama
120W
90W
60W
m/s
Climatology
Significant background cyclonic vorticity
Ample background precipitation favorable for easterly wave
growth, with maximum in bight of Panama
120W
90W
60W
m/s
Regions for easterly wave climatology
East
Pacific
Caribbean
Atlantic
Composites
Bight of
Panama
Bight of
Panama
Bight of
Panama
The composite of easterly waves suggests that waves in
the Atlantic do not cross into the Pacific and that they
originate near the bight of Panama
The lag correlation of 2–10 day meridional wind
anomalies suggests that waves in the Atlantic do
not cross over into the Pacific
Bight of
Panama
Furthermore, east Pacific waves look to develop
around the bight of Panama
Bight of
Panama
mm/day
An easterly wave is first identified near Panama on
6 August
mm/day
Two days later, the wave has moved to near
El Salvador, while gaining strength
mm/day
Finally on 10 August, the wave has intensified and
moved near the Mexican coast
Observations support similar origin, track and intensity of
the modeled wave
Lag -2
m/s
m/s
m/s
Summary
The bight of Panama is a climatologically favorable for the
development of easterly waves due to the low-level cyclonic flow
and precipitation maximum
Composites of easterly waves support the idea that most easterly
waves are formed in east Pacific rather over Africa
Composites and lag correlation plots, support the idea that waves
do not cross over from the Atlantic to the Pacific
The WRF model simulates the location, track, and intensity of
easterly waves when compared to observations in a case study
Future work
Use the WRF model to determine whether
easterly waves can be simulated in the east
Pacific without intrusion of easterly waves from
the Atlantic
Use WRF to determine importance of Panama
Bight convection for seeding easterly waves
Correlate the east Pacific developing waves with
tropical cyclone frequency
Thank you
Questions?