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”

~90°N ~30°N Hadley Cell ~0° ~30°S Costa Rica ~ 8-11.5°N ~90°S HIGH Northeast Trades LOW LOW LOW ~0° HIGH HIGH HIGH ~30°S Costa Rica ~ 8-11.5°N HIGH ~90°S

STANDARD CLIMATOLOGICAL PICTURE Northeast Trades Andes

“Hot air can cold more water vapor than cold air.” CLAUSIUS – CLAPEYRON

Cool 18°F Released condensation 17 g. kg-1 Cool 10°C

Central Guanacaste Tilarán Talamanca Source: NASA

Source: Instituto Merteorologico Nacional and Instituto Costarricense de Electricidad

Act 2: May - October “ITCZ”

~90°N Warm Air Converging And Rising I.T.C.Z. ~30°N Hadley Cell ~0° HIGH HIGH HIGH ~30°N Hadley Cell Northeast Trades LOW LOW LOW ~0° HIGH HIGH HIGH ~30°S ~90°S

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

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

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

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

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

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

Caribbean Low Level Jet (CLLJ) DJF 1000hPa NCEP-NCAR RE-ANALYSIS Source: Kalnay et al., 1996 m/s

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

GAP IN CENTRAL AMERICAN CORDILLERA

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

Act 4: November - April “Los Nortes”

HIGH ~90°N November – March ~45-60°N COLD COLD ~30°N ~0° LOW LOW LOW Northeast Trades ~0° LOW LOW LOW

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

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

Act 4: ENSO “El Niño y La Niña”

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

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

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

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

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

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

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

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 ? Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean

Act 5: Epilogue “The Atlantic”

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 Seasonal Precipitation as a Normalized deviate Standard Deviations above/below mean