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

2. 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)

3. Act 1: November - April
“Los Alisios”

4. ~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
~ °N
HIGH
~90°S

5. STANDARD CLIMATOLOGICAL PICTURE
Northeast
Trades
Andes

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

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

9. Central
Guanacaste
Tilarán
Talamanca
Source: NASA

10. Source: Instituto Merteorologico Nacional and Instituto Costarricense de Electricidad

11. Act 2: May - October
“ITCZ”

12. ~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

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

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

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

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

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

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

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

22. 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

23. GAP IN CENTRAL AMERICAN CORDILLERA

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

26. Act 4: November - April
“Los Nortes”

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

28. 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

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

31. Act 4: ENSO
“El Niño y La Niña”

32. 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

33. 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

34. 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

35. 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.”

36. 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.”

37. 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.”

38. 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.”

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

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

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

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

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

44. Act 5: Epilogue
“The Atlantic”

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

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

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

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

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