Precipitation Climatology of Costa Rica and its Variability Atmospheric, Oceanic and Topographic Interactions

Characters in The Play Topography Oceans Northeast Trade Winds (aka Los Alisios) Caribbean Low Level Jet (aka Veranillos de San Juan) Inter-tropical Convergence Zone Cold Fronts (aka Los Nortes) ENSO (El Niño y La Niña)

Act 1: November - April “Los Alisios”

LOW HIGH ~0° ~30°S ~30°N ~45-60°S ~45-60°N ~90°S ~90°N Northeast Trades Hadley Cell Costa Rica ~ °N

Northeast Trades Andes STANDARD CLIMATOLOGICAL PICTURE

Source: NASA

Source: Instituto Merteorologico Nacional and Instituto Costarricense de Electricidad

Act 2: May - October “ITCZ”

ITCZ Feb 3°N Northeast Trades Andes STANDARD CLIMATOLOGICAL PICTURE Peru- Humboldt Current

ITCZ Feb 3°N Northeast Trades Andes STANDARD CLIMATOLOGICAL PICTURE Cross- Equatorial Westerlies

10°N Northeast Trades Andes STANDARD CLIMATOLOGICAL PICTURE ITCZ Sep Cross-equatorial Westerlies

Act 3: July - August “Veranillo de San Juan”

VERANILLOS DE SAN JUAN OR CANICULA Mid-Summer Drought Month Average Latitude (°N) of ITCZ in Eastern Equatorial Pacific Hastenrath, 1991

San Andrés or Caribbean Low Level Jet Cool Upwelling GAP IN CENTRAL AMERICAN CORDILLERA

DJF 1000hPa m/s NCEP-NCAR RE-ANALYSIS Source: Kalnay et al., °W Caribbean Low Level Jet (CLLJ)

SEASONAL STRENGTHS OF CLLJ Westerly Component of Wind Velocity at 80°W MAM JJA SON DJF Source: NCEP-NCAR Reanalysis, Kalnay et al., 1996 CLLJ Latitude Pressure (mm) ~Altitude

GAP IN CENTRAL AMERICAN CORDILLERA

JUNE JULY AUGUST SEPTEMBER EVIDENCE OF VERANILLOS ? Source: Mejia and Poveda 2003 Meso-Scale Convective Systems 1998 as detected by TRMM

Act 4: November - April “Los Nortes”

H H Rockies etc. Appalachians North America as Funnel of Cold Air in Boreal Winter Surges of Cold Air over Gulf of Mexico and Caribbean

ITCZ Feb 3°N Northeast Trades Cold Fronts Andes STANDARD CLIMATOLOGICAL PICTURE

Act 4: ENSO “El Niño y La Niña”

ITCZ Feb 3°N Northeast Trades Andes STANDARD CLIMATOLOGICAL PICTURE EL NIŇO Peru- Humboldt Current 1. Warmer surface waters appear in Eastern Equatorial Pacific November onwards

ITCZ Feb 3°N Northeast Trades Andes STANDARD CLIMATOLOGICAL PICTURE EL NIŇO Peru- Humboldt Current 1. Warmer surface waters appear in Eastern Equatorial Pacific November onwards 2. ITCZ shifts south and west of normal position

ITCZ Feb 3°N Northeast Trades Andes STANDARD CLIMATOLOGICAL PICTURE EL NIŇO Peru- Humboldt Current 1. Warmer surface waters appear in Eastern Equatorial Pacific November onwards 2. ITCZ shifts south and west of normal position 3 Northeast Trades intensify

Positive = More Westerly (Less Easterly) Negative = More Easterly (Less Westerly) Difference in Velocities (Warm – Cold Phase of ENSO) MAM Poveda et al., 2001 “In El Niño, trades weaker (less easterly) than in La Niña.” Spring:

JJA Poveda et al., 2001 “In El Niño, trades stronger (less westerly) than in La Niña.” Summer: Positive = More Westerly (Less Easterly) Negative = More Easterly (Less Westerly) Difference in Velocities (Warm – Cold Phase of ENSO)

SON Poveda et al., 2001 “In El Niño, trades stronger (less westerly) than in La Niña, but not as marked as in summer.” Fall: Positive = More Westerly (Less Easterly) Negative = More Easterly (Less Westerly) Difference in Velocities (Warm – Cold Phase of ENSO)

DJF Poveda et al., 2001 “In El Niño, trades much weaker (less easterly) than in La Niña.” Winter: Positive = More Westerly (Less Easterly) Negative = More Easterly (Less Westerly) Difference in Velocities (Warm – Cold Phase of ENSO)

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño ?

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño ?

Act 5: Epilogue “The Atlantic”

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño

Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean La Niña El Niño