Climate of an oceanic island in the Eastern Pacific: Isla del Coco, Costa Rica, Central America Eric J. Alfaro1,2,3, Hugo G. Hidalgo1,2 1. Center for Geophysical Research, University of Costa Rica, 11501-2060 San José, Costa Rica; erick.alfaro@ucr.ac.cr, hugo.hidalgo@ucr.ac.cr 2. School of Physics, University of Costa Rica, 11501-2060 San José, Costa Rica. 3. Marine Sciences and Limnology Research Center (CIMAR), University of Costa Rica, 11501-2060 San José, Costa Rica. Received 06-III-2015. Corrected 05-V-2015. Accepted 27-V-2015. Abstract: Studies of atmosphere-ocean interaction in the Pacific of Costa Rican are scarce. To identify oceano- graphic systems that may be influencing climate near Cocos Island (Eastern Tropical Pacific Seascape) we conducted six scientific expeditions between 2007 and 2012. Two automated weather stations were set near Chatham and Wafer bays during the expeditions. Data included records from National Meteorological Institute, Global Precipitation Climatology Project (GPCP) and Extended Reconstructed Sea Surface Temperature (ERSST). The climate is typical of the Eastern Tropical Pacific. Its seasonality is driven by precipitation vari- ability associated with meridional migration of the Intertropical Convergence Zone. The seasonal cycle has two peaks, in May and July, a relative minimum between them in June, and the absolute minimum in February. Most of the precipitation is recorded from April to November. Most rain events have short duration and low intensity. An SST trend was observed from January 1854 to December 2013, coherent with regional warming temperature observations. From 1998 to 2013 there were changes in distributions of almost all meteorological parameters. The combination of these factors resulted in higher evapotranspiration values through the daily cycle, especially during the night time. Precipitation (P) positive anomalies tended to be associated with positive air surface tem- perature (AST) and SST anomalies and negative global radiation (GR) anomalies. Negative P anomalies tended to be associated with negative AST, SST and positive GR anomalies. Relative humidity (RH) negative anoma- lies tend to be associated with positive wind speed (WS) anomalies, and the WS effect is opposite for positive RH anomalies. During the cold Niño 3 condition of October 2007, negative P, AST, SST and RH anomalies were observed in concordance with positive WS and GR anomalies, in agreement with the conceptual model of climate system response at Isla del Coco to cold ENSO conditions. Rev. Biol. Trop. 64 (Suppl. 1): S59-S74. Epub 2016 February 01. Key words: Isla del Coco, Cocos Island, Costa Rica, Eastern Tropical Pacific, climate. Even though atmosphere-ocean interac- Pacific Ocean’s climate, it was very important tion is a key point in oceanography research and practical for Costa Rica to establish an (e.g. Fiedler, & Lavin-Peregrina, 2006; Lavin- observatory on Isla del Coco. Peregrina et al., 2006), studies related to atmo- In spite of the importance of meteorologi- spheric aspects in this specific part of the cal monitoring, measurements have been scat- Costa Rican Eastern Tropical Pacific Seascape tered in space and time around this site, mainly (ETPS) are still scarce (Cortés, 2012a,b; 2014). because of its distance from the continent, Henry Pittier pointed out the importance of along with the associated costs for the expedi- Isla del Coco for geophysical research at the tions and maintenance of permanent stations. end of the 19th century (Pittier, 1898; Alfaro, Although these short records of meteorologi- 2008). He recognized that to understand the cal variables allowed the description of main Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 S59 climatic aspects of the island (e.g. Fernández, ITCZ. In general, seasonal variations at Isla del 1984; Herrera, 1985; Alfaro, 2008; Quirós- Coco were observed to be mainly associated Badilla, & Alfaro, 2009), Cortés, Morales, with the meridian migration of the ITCZ; as the Alfaro, Lizano & Acuña (2010) recommended island is under its direct influence from boreal the reinstallation of an automated meteorologi- Spring to Autumn. Results showed that warm cal station at Isla del Coco by the Costa Rican ENSO events modulates that ITCZ migration National Meteorological Institute (IMN for its and tend to be associated with above normal name in Spanish). This recommendation was precipitation and temperature seasons at Isla attended and meteorological measurements del Coco and vice versa. The eastern Pacific started again in August 2010, finishing a gap warm pool, a region of warm water southwest since November 2002. of Mexico, is a region of relatively weak zonal Summarizing the Isla del Coco basic winds, potential convective activity and tropical climate characterization, Alfaro (2008) and system development (Amador et al., 2006). Its Quirós-Badilla & Alfaro (2009) observed that effects on Isla del Coco climate are unknown. January, February and March (JFM) had the A more detailed examination of the relevant lowest precipitation accumulations, followed atmospheric forcing, on annual and seasonal by an intense rainy season between April time scales, in the eastern tropical Pacific region and December, with showers reported mainly is presented by Amador et al. (2006). during the afternoon. The warmest tempera- The first objective of this work was to tures were observed in JFM, showing a small present the meteorological measurements col- decrease from June to December. JFM also lected during the scientific expeditions from had the highest net radiation values and the 2007 to 2012 and to compare these observa- lowest relative humidity (RH) and wind speed tions with climate values from weather stations (WS) values near noon hours. The air in motion that operated on the island. These comparisons toward equatorial regions caused by the pres- through graphic anomalies can also be useful sure gradient between the tropics and subtrop- in the interpretation of results for the other ics is known as the trade winds and is observed project components, especially because no as northeasterlies in the northern hemisphere meteorological station functioned permanently and southeasterlies in the southern hemisphere at the island during the 2007-2010 expeditions. due to the effect of the Coriolis acceleration A second objective was the analysis of the new (Amador, Alfaro, Lizano, & Magaña, 2006). IMN records and the comparison of them with The trade winds converge toward low latitudes previous ones, specifically between 2010-2013 (Hastenrath, 1991), carrying moisture and forc- and 1998-2001. This can be useful in trend ing the air into a region of strong upward detection and homogeneity using time series motion, the Inter-Tropical Convergence Zone analysis, and compared with gridded data sets (ITZC; Amador et al., 2006). According to in the ETPS area context. Amador et al. (2006), the low level zonal cir- culations observed over the eastern tropical MATERIALS AND METHODS Pacific are part of the trade wind system at low latitudes and present regions of convergence- The use of automated weather stations divergence that are very important for defining allowed making meteorological measurements ocean surface mean properties associated with at Isla del Coco, Costa Rica, located in the the SST distribution and the warm pool region. ETPS. The stations were set up at Chatham The trade winds constitute an important meridi- (5º32’51” N, 87°02’43” W, 142 m.a.s.l.) and onal energy and moisture exchange mechanism Wafer (5º32’24” N - 87º03’26” W, 132 m.a.s.l.) (as part of the low level branch of the Hadley bays. Data were registered every 5min and cell) that determines to a great extent the pre- hourly values were generated. Variables ana- cipitation distribution in the region, i.e., the lyzed in this work included hourly-accumulated S60 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 precipitation (P) and global radiation (GR) N - 87º03’20” W, 11 m.a.s.l.). Data can be defined as the total incoming radiation, along downloaded from http://www.unavco.org/ with average air and sea surface temperature data/gps-gnss/data-access-methods/dai1/raw_ (AST and SST respectively), RH and WS. rinex_by_download.php?sid=5588&parent_ Measurements were recorded during the expe- link=Permanent&pview=original. As it was ditions on: October 12-17, 2007, April 5-11, done for the IMN station, the monthly aver- 2008, March 1-6, 2009, April 22-27, 2010, age corresponding to the same month of the July 2-8, 2011 and March 15-21, 2012. Davis expedition and the entire period averages were weather stations, Vantage Pro Plus/Vantage calculated for comparison, except for GR, Pro2 Plus type, were used during all the expe- which was not observed at this site. Seasonal ditions except in October 2007 in which a cycles for maximum and minimum temperature Campbell, CR10X type was used in Chatham (Tmax and Tmin) were also analyzed for this Bay. No measurements were collected in Wafer station record. during this first expedition. Additionally, Kes- The GPS-COCONet data at temporal reso- trel 4500 NV portable stations were installed lutions of one and five minutes were used to on the ship anchored at Chatham Bay during determine the typical storm duration and inten- the last five expeditions. sity. For some of the analyses a comparison Hourly records were obtained from the between the meteorological variables for an IMN weather station located in Chatham Bay early period (September 1, 1998 to August 31, (5°32’51”N, 87°02’42”W, 151 m.a.s.l.), coded 2001) and a later period (September 1, 2010 as 200002. The records obtained were divided to August 31, 2013) was performed using the in two parts. First, from 11:00 August 30, 1998 data from the IMN, but filling the missing data to 18:00 November 1, 2002, and second, from using the GPS data by establishing relation- 18:00 August 30, 2010 to 16:00 September 9, ships between the percentiles of the datasets 2013. For comparison with the weather sta- during a common period. The comparison tions installed during the campaigns, monthly between the periods during the rainy and dry average values corresponding to the month of seasons was done using cumulative density the expedition from these IMN records were functions and a Kolmogorov-Smirnov test in calculated for the same atmospheric variables order to determine if the data from both periods obtained during the campaigns. Additionally, could be considered to have the same distribu- monthly average values when IMN data were tion or not. available during the last two expeditions and The hourly measurements of net radiation, the whole period of record averages were AST, RH and WS from the IMN data (filled calculated for these same variables. Seasonal with GPS) were used to compute the reference cycles of dew point temperature and sea level evapotranspiration (ETo) for the early and late pressure (SLP) were also analyzed for the sec- periods described above, with the objective to ond part of the record in this station, as they detect differences between them. Reference were not available for the first part. evapotranspiration is a hydrological term, it is Additionally, the one or five minute referred to the evapotranspiration for a hypo- records of a GPS automated weather station, thetical grass reference crop with an assumed were obtained from the COCONET project crop height of 0.12m, a fixed surface resistance (http://facility.unavco.org/gsacws/gsacapi/site/ of 70sm-1 and an albedo of 0.23. search?site.group=COCONet, Protti, González, Precipitation data from the Global Pre- Freymuller, & Doelger, 2012) and hourly data cipitation Climatology Project (GPCP; Adler were produced from them, covering from et al., 2003), version 2.2, were provided by 14:00 May 18, 2011 to 17:00 September 19, the National Oceanographic and Atmospheric 2013. The station was coded as CocosIsl_ Administration (NOAA), Office of Ocean- CRI2011 and located in Wafer Bay (5º32’40” ic and Atmospheric Research, Earth System Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 S61 Research Laboratory, Physical Sciences Divi- point centered at 6º N - 88º W which covers the sion, Boulder, Colorado, United States, from area 5-7º N - 87-89º W. Composites of average their website (http://www.esrl.noaa.gov/psd/). grid-point differences were estimated, similar The data are combinations of satellite and rain- to the gridded precipitation analysis described gauge sources and were available from January previously using Adler et al. (2003) data. The 1979 to October 2013. The spatial resolution spatial resolution of the data is 2×2º. of the data is 2.5×2.5º. The grid-point cen- Finally, the Tropical Rainfall Measurement tered at 6.25º N - 86.25º W, covering the area Mission (TRMM) (Huffman et al., 2007) data 5-7.5º N - 85-87.5º W, was studied and also were used in a precipitation trend analysis. the precipitation average grid point differences TRMM is a joint mission between the National composites between 2010-2013 and 1998-2001 Aeronautics and Space Administration (NASA) for April-November and December-March sea- and the Japan Aerospace Exploration Agency sons. The area that covers the composites was (JAXA). In this study, the 3B42 estimates 3-22º N - 73-97º W. version 6 were chosen. These estimates cor- SSTs were obtained from four sources dur- respond to a 3-hourly average centered at the ing the expeditions. Surface values (<2m deep) middle of each 3-hour period (i.e., 0Z, 3Z, 6Z, measured with the conductivity, temperature, 9Z, 12Z, 15Z, 18Z, and 21Z). The final 3B42 and depth of the ocean instrument or CTD product data are available at 0.25x0.25º spatial (Lizano, & Alfaro, 2014) and Niskin bottles resolution extending from 50º S - 50º N. For the using an YSI sensor (Acuña-González, García- present study, the period 1998-2009 was used. Céspedes, Gómez-Ramírez, Vargas-Zamora, In order to transform the satellite precipita- & Cortés, 2008) from oceanographic stations tion data into a daily frequency, it was neces- around the island. The values were also mea- sary to merge the 3-hourly data, considering sured in the current meter anchored at Wafer the local time. Bay (<2m deep) during the first expedition (Lizano, & Alfaro, 2004). For comparison the RESULTS Extended Reconstructed Sea Surface Tempera- ture (ERSST) (Smith, Reynolds, Peterson, & Precipitation seasonal and daily cycles are Lawrimore, 2008) dataset was included. It was shown in Figure 1 for IMN and GPS-COCON- provided by the International Research Institute et weather stations. Figure 1A incorporated for Climate and Society, The Earth Institute, data collected after August 2010 and agreed in Columbia University, New York, United States, general terms with previous results of Alfaro from their website (http://iridl.ldeo.columbia. (2008) and Fernández (1984). About 88 % of edu/). ERSST is a global monthly sea surface the precipitation was recorded from April to temperature analysis derived from the Inter- November, with showers during the afternoon. national Comprehensive Ocean-Atmosphere The seasonal cycle had two peaks in May and Data Set with missing data filled in by statisti- July with more than 19 mm day-1 and a relative cal methods. This monthly analysis begins in minimum between them in June diminishing January 1854 continuing to December 2013. to 15-16mm day-1, with the absolute minimum The newest version of ERSST (3b) used in in February, <4mm day-1. The daily cycle also this work is optimally tuned to exclude under- exhibited a secondary maximum in the early sampled regions for global averages and does morning around sunrise. Data records used to not include satellite data. For this data set the calculate the seasonal and daily cycles (Fig. long-term monthly average values correspond- 1B) were considerable less than those used ing to the respective months of the expedition in Fig. 1A, but the figure was included for and the specific monthly values during the comparison. Absolute maximum and minimum expeditions were also extracted among the values in the seasonal cycle were also present whole period of record average for the grid in July and February respectively in the data S62 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 A 24 1.8 GPS data can be used to characterize show- 22 1.6 ers observed at Isla del Coco. Figure 2 shows 20 1.4 histograms of duration and intensity using one 18 and five minute time resolutions. They reflect 16 1.2 processes associated with short-lived events of 14 1.0 12 low intensity values, most probably a reflection 0.8 10 of events originated from tropical convection 8 0.6 (Alfaro, 2008). 6 0.4 Because of the temporal resolution avail- 4 0.2 able for this GPS station, it was possible to 2 characterize seasonal cycles for Tmin and 2 4 6 8 10 12 Month Tmax (Fig. 3). Maxima for both curves were B 24 1.8 observed in March-April, previous to the April- 22 1.6 November rainy season. The mean difference 20 1.4 between them was 0.7°C, and the lower tem- 18 1.2 peratures were observed from July to Decem-16 14 ber. However, variations through the year were 1.0 12 less than 2°C. Conversely, dew point tempera- 0.8 10 ture from IMN station is highest in August and 8 0.6 lowest in October, with a difference of 2.8°C 6 0.4 between them (Fig. 3). This variable was 4 0.2 not reported previous to 2010. According to 2 2 4 6 8 10 12 Alfaro (2008), this result agreed with a relative Month minimum and a maximum observed in the WS Fig. 1. Seasonal (horizontal axis) and daily (vertical axis) during those months. Mean values for the three precipitation (mm hour-1) cycles of the automatic a) IMN curves observed in Figure 3 were 25.5, 24.8 and b) GPS weather stations in Chatham and Wafer Bay, and 22.2°C respectively. respectively. Monthly average SLP for the automated IMN weather station located in Chatham Bay from this GPS weather station; and its daily is presented in Figure 4. March and October cycle also exhibited a secondary maximum show the minimum and maximum values, with around sunrise, with most of the showers a difference between them of approximately in the afternoon. 2.2hPa. Mean value observed was 1015hPa. Duration Histogram Intensity Histogram 80 40 70 60 30 50 40 20 30 20 10 10 0 0 100 101 102 1 2 3 4 5 6 Log Duration (minutes) Intensity (mm) Fig. 2. Duration and intensity of rainfall for data with a resolution of 1 minute (blue) and 5 minutes (red). Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 S63 Frequency (%) Hour Hour Frequency (%) 28 significant trend was observed in the long-term 26 record from January 1854 to December 2013. This SST positive trend was observed in other 24 locations near Costa Rica’s ETPS (Alfaro et 22 al., 2012; Morales-Ramírez, Lizano, Acuña, 20 Alfaro, & Gómez, 2015) and was coherent with 1 2 3 4 5 6 7 8 9 10 11 12 regional warming temperature observations Month reported by the IPCC (Bindoff et al., 2013). Fig. 3. Diamond (squared) line is for the monthly average Figure 7 shows the mean values measured of minimum (maximum) temperatures for the automatic at Isla del Coco during the expeditions for P, GPS weather station in Wafer Bay. Triangle line is dew AST, RH, GR, WS and SST. When climate point temperatures for the automatic IMN weather station in Chatham Bay. norms from IMN, GPS and Smith et al. (2008) data were compared with measurements from the first expedition (October 12-17, 2007), 1016 it was observed that this expedition present- ed negative anomalies for P, AST and SST 1015.5 (except for the current meter’s value located in Wafer) and positive anomalies for GR and 1015 WS. October 2007 presented a negative Niño 3 SSTA index anomaly of -1.20°C (using data 1014.5 from http://www.cpc.ncep.noaa.gov/data/indi- ces/ersst3b.nino.mth.81-10.ascii). The tropical 1014 Pacific Niño 3 index area (5° S - 5° N, 90 - 150° W) is the nearest to Isla del Coco and was used 1013.5 2 4 6 8 10 12 in the ENSO variability study (Quirós-Badilla, Month & Alfaro, 2009). Anomalies recorded during Fig. 4. Monthly average of sea level pressure for the the first expedition agreed with the P, AST and automated IMN weather station in Chatham Bay. SST behavior expected for cold ENSO condi- tions, according to Quirós-Badilla & Alfaro (2009). During the other expeditions, Niño 3 This variable was also not reported previous index showed values close to what it is consid- to 2010, but Fernández (1984) also observed ered ENSO neutral conditions (-0.5 ≤ Niño 3 ≤ high-pressure values during October-Novem- 0.5°C, approximately). The second expedition ber and the lowest value in March. These val- (April 5-11, 2008) presented positives anoma- ues could be related with the meridional ITCZ lies for P (except for Wafer station), AST, seasonal migration. TSM and WS (except for Chatham station) A positive but statistically insignificant and negative anomalies for RH and GR. The precipitation trend was detected for the grid third expedition (March 1-6, 2009) presented point centered at 6.25º N - 86.25º W, from positive anomalies for P, RH, WS (except for January 1979 to Oct 2013 (Fig. 5), and for Chatham) and SST and negative anomalies for the TRMM data as well. Maldonado & Alfaro AST (except for the measurements in the ship (2012) noticed that Isla del Coco is located in anchored at Chatham Bay) and GR. SST grid a region with observed negative trends in the point monthly value anomaly was negative North and positive ones in the South, in agree- during that expedition. The fourth expedition ment with the small trend value of Figure 5. (April 22-27, 2010) presented positive anoma- This result contrasted with the one obtained lies for P, AST, SST and WS, and negative for SST in the grid point centered at 6º N - anomalies for RH (except for the measure- 88º W (Fig. 6), in which a positive statistical ments in the ship anchored at Chatham Bay) S64 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 Pressure (hPa) Temperature (ºC) 22 20 18 16 14 12 10 8 6 4 2 1980 1985 1990 1995 2000 2005 2010 Year Fig. 5. Monthly precipitation (gray line), average of 7.8 mm/day (horizontal line). Linear trend (solid black line) is 0.03mm/ (day*year), with a p-value of 0.12, measured from January 1979 to October 2013. Grid point centered at 6.25º N- 86.25º W covering the area 5-7.5º N - 85-87.5º W. Blue and red lines are the smoothed times series using a triangular moving average of 3 and 10 years, respectively. Data from Adler et al. (2003). 30 29.5 29 28.5 28 27.5 27 26.5 26 25.5 1860 1880 1900 1920 1940 1960 1980 2000 Year Fig. 6. Monthly sea surface temperatures (gray line), average of 27.6ºC (horizontal line). Linear trend (solid black line) is 0.0017ºC/year, with a p-value ˂ 0.01, measured from January 1854 to December 2013. Grid point centered at 6° N - 88° W covering the area 5-7° N - 87-89° W. Blue and red lines are the smoothed times series using a triangular moving average of 3 and 10 years, respectively. Data from Smith et al. (2008) Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 S65 Precipitation (mm/day) Temperature (ºC) A 2 B 28 1.8 27.5 1.6 27 1.4 26.5 1.2 26 1 25.5 0.8 25 0.6 0.4 24.5 0.2 24 0 CCI CCII CCIII UUCI UUCIV UUCV 23.5 CCI CCII CCIII UUCI UUCIV UUCV Cruise Cruise C D 95 1.6 1.4 90 1.2 1 85 0.8 0.6 80 0.4 0.2 75 0CCI CCII CCIII UUCI UUCIV UUCV CCI CCII CCIII UUCI UUCIV UUCV Cruise Cruise E F 3.5 30 3 29.5 2.5 29 2 28.5 1.5 28 1 27.5 0.5 27 0 CCI CCII CCIII UUCI UUCIV UUCV 26.5 CCI CCII CCIII UUCI UUCIV UUCV Cruise Cruise Fig. 7. Mean (A) Precipitation (P), (B) Average Surface Temperature (AST), (C) Relative Humidity (RH), (D) Global Radiation (GR), (E) Wind Speed (WS) and (F) Sea Surface Temperature (SST) values measured at Isla del Coco during the expeditions of October 2007 (CCI), April 2008 (CCII), March 2009 (CCIII), April 2010 (UUCI), July 2011 (UUIV) and March 2012 (UUV). For (A), (B), (C), (D) and (E), black and white triangles are for the values measured at Chatham and Wafer Bay, respectively. Black circles are for the values measured in the ship anchored at Chatham bay. For comparison we include the monthly average values corresponding to the month of the expedition from the Costa Rican NMI and GPS- S66 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 Wind Magnitude (m/s) Humidity (%) Precipitation (mm/hour) Temperature (ºC) Global Radiation (MJ/m2) Temperature (ºC) A 2.5 20ºN 2 1.5 1 15ºN 0.5 0 10ºN -0.5 -1 -1.5 5ºN -2 -2.5 95ºW 90ºW 85ºW 80ºW 75ºW Longitude B 2.5 20ºN 2 1.5 1 15ºN 0.5 0 -0.5 10ºN -1 -1.5 5ºN -2 -2.5 95ºW 90ºW 85ºW 80ºW 75ºW Longitude Fig. 8. Precipitation (mm/day) average grid point differences between 2010-2013 and 1998-2001 for (A) April-November and (B) December-March seasons. For the grid point centered at 6.25° N - 86.25° W covering the area 5-7.5° N - 85-87.5° W, the values are -0.10 and -0.02mm/day, both with p-values > 0.10. Data from Adler et al. (2003). Black square is Isla del Coco. and GR. The fifth expedition (July 2-8, 2011) observed in the IMN station were slightly presented positive anomalies for P, AST, TSM negative when compared to the climate record (except for the YSI measurements) and WS (no value for July) and negative anomalies for RH. measurements of WS were done in Chatham Average monthly AST values observed in the during this expedition, but monthly values IMN and GPS stations were slightly lower than COCONET stations located in Chatham and Wafer bay (black and white squares respectively); and the monthly average values when data were available when they worked during the expeditions (black and white diamonds respectively). Solid and dashed horizontal lines are the period of record averages available from the NMI and GPS stations respectively. For (F), Black triangles and stars are for the surface values (< 2m deep) measured with CTD and YSI equipments at stations around the island. Black circle is for the values measured in the current meter anchored at Wafer bay (< 2m deep). For comparison we include the monthly average values of the Smith et al. (2008) record, black squares; the average monthly values for the same record during the expeditions, black diamonds and the record average, solid horizontal line. Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 S67 Latitude Latitude A 20ºN 0.4 0.3 15ºN 0.2 0.1 10ºN 0 5ºN -0.1 95ºW 90ºW 85ºW 80ºW 75ºW Longitude B 20ºN 0.4 0.3 15ºN 0.2 10ºN 0.1 0 5ºN -0.1 95ºW 90ºW 85ºW 80ºW 75ºW Longitude Fig. 9. Sea surface temperature (°C) average grid point differences between 2010-2013 and 1998-2001 for (A) April- November and (B) December-March seasons. For the grid point centered at 6° N - 88° W covering the area 5-7° N - 87-89° W, the values are 0.32 and 0.25°C, both with p-values > 0.10. Data from Smith et al. (2008). Black square is Isla del Coco. climate norms and RH value slightly higher SST average grid-point differences between in the GPS station. The March 15-21, 2012 the years 2010-2013 and 1998-2001 in the expedition presented positive anomalies for area 3-22º N - 73-97º W for April-November P, AST, SST and WS and negative anomalies and December-March seasons were calculated for RH and GR. Average monthly AST values (Figs. 8 and 9) (data from Adler et al., 2003 observed in the GPS station were slightly lower and Smith et al., 2008). Precipitation and SST than climate ones. differences for the grid-point that covers Isla In agreement with the two periods that del Coco were not statistically significant in all the IMN station worked, the precipitation and cases. For precipitation, the island is located S68 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 Latitude Latitude in a region of transition between negative with showers usually during the afternoon as it differences in the northeast and positive ones was identified in Alfaro (2008) (Fig. 1). There in the southwest, especially during the April- are many short-duration rain events with low November season and over the Central Ameri- intensity (Fig. 2). Interannual precipitation can isthmus (Fig. 8A). The region of negative variability was driven by ENSO, in which differences over the Chocó, one of the rainiest Niño 3 region had an important role modulat- places on the earth is notorious (Amador et ing the ITCZ migration (Quirós-Badilla, & al., 2006). Figure 9 shows that Isla del Coco Alfaro, 2009). This issue modulated also the is embedded in a broad region of positive SST interannual AST and SST variability in which differences during April-November, and in a normally Niño 3 warm and cold events tended transition area between positive values in the to be associated with positive and negative P, northwest and negative ones in the east. In both AST and SST anomalies. A non-significant seasons, the Caribbean Sea showed a broad statistically precipitation trend was detected for area of positive differences. the grid point centered at 6.25º N - 86.25º W Figure 10 compares the CDFs for the (Fig. 5).There was little difference in the daily same (previously defined) periods recorded and seasonal temperature cycles, observing at the IMN station in Chatham. There was no that dew point temperature was driven by WS difference in P during April-November, but it through the year (Fig. 3). Similar character- was drier for December-March as in Figure 8. istics of the daily and seasonal cycles of SLP In agreement with Figure 9, warmer values were observed (Fig. 4). A positive statistically were more frequent for the late period in both significant SST trend was observed from Janu- seasons, and during this period lower values ary 1854 to December 2013 (using data from for RH and WS were more frequent. Southwest Smith et al., 2008) in the grid point centered winds were more frequent in April-November, at 6º N - 88º W (Fig. 6). This behavior was but Southeast ones were more frequent in observed for other locations near Costa Rica’s December-March when two periods were com- ETPS (Morales-Ramírez et al., 2015; Alfaro pared. Higher net radiation values were more et al., 2012) and was coherent with regional frequent also in the late period, especially warming temperature observations reported during April-November. The combination of by the IPCC (Bindoff et al. 2013). There were those factors described previously resulted changes in the statistical distribution of all in higher reference evapotranspiration (ETo) variables including ETo, except for P and net values through the daily cycle (Fig. 11), espe- radiation during April to November, when the cially during night-time. The ultimate causes early and late periods were compared (Figs. 10 of the increase in ETo during the night are still and 11). It should be noted that the influence of unknown, but they could be related to changes decadal scale climate variations (e.g. Enfield, in RH and WS during those hours. & Mestas-Nuñez, 1999; Mestas-Nuñez, & Enfield, 1999) could be partially responsible DISCUSSION for these fluctuations; but future analysis with more in situ data should be done to confirm Isla del Coco showed a climate regime these findings. typical of the ETPS. Its seasonality is driven Local meteorological measurements are by precipitation variability associated with the also important in multidisciplinary research to meridian migration of ITCZ (Amador et al., properly understand the Isla del Coco oceano- 2006). The seasonal cycle had two precipitation graphic systems (Cortés, 2008; 2012c), as part peaks, May and July, and a relative minimum of the broader ETPS (Henderson, Rodríguez, between them in June, with the absolute mini- & McManus, 2008). In general terms, the mum during February. Most of the precipita- meteorological observations collected during tion was recorded from April to November, the expeditions to Isla del Coco showed that Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 S69 Rainy season (May.-Nov.) Dry season (Dec.-Apr.) 1 1 Early period Late period 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 A) B) N.S. 0 0 101 101 log Prec (mm) log Prec (mm) 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 C) N.S. D) N.S. 0 0 20 22 24 26 28 30 20 22 24 26 28 30 Temp. (ºC) Temp. (ºC) 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 E) N.S. F) N.S. 0 0 60 70 80 90 100 60 70 80 90 100 RH (%) RH (%) 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 G) N.S. H) N.S. 0 0 0 2 4 6 8 0 2 4 6 8 Mag (m/s) Mag (m/s) Fig. 10. Empirical cumulative density functions for early (September 1, 1998 to August 31, 2001) and late (September 1, 2010 to August 31, 2013) periods for various parameters and seasons. If the data for both periods can be considered to not come from the same distribution according to a Kolmogorov-Smirnov test, the subfigure is labeled with the letter “N.S.”. Prec: precipitation, Temp: temperature, RH: relative humidity, Mag: wind speed magnitude, U: zonal wind speed component, V: meridional wind speed component, and Rn: net radiation. S70 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 cdf cdf cdf cdf cdf cdf cdf cdf Rainy season (May.-Nov.) Dry season (Dec.-Apr.) 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 I) N.S. J) N.S. 0 0 -4 -2 0 2 -4 -2 0 2 U (m/s) U (m/s) 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 K) N.S. L) N.S. 0 0 -5 0 5 10 -5 0 5 10 V (m/s) V (m/s) 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 M) N) N.S. 0 0 0.5 1 1.5 2 2.5 3 3.5 4 0.5 1 1.5 2 2.5 3 3.5 4 Rn (W/m2) Rn (W/m2) Fig. 10. (Continued) Empirical cumulative density functions for early (September 1, 1998 to August 31, 2001) and late (September 1, 2010 to August 31, 2013) periods for various parameters and seasons. If the data for both periods can be considered to not come from the same distribution according to a Kolmogorov-Smirnov test, the subfigure is labeled with the letter “N.S.”. Prec: precipitation, Temp: temperature, RH: relative humidity, Mag: wind speed magnitude, U: zonal wind speed component, V: meridional wind speed component, and Rn: net radiation. positive (negative) P anomalies tended to be above the ocean, associated with more (less) associated with positive (negative) AST and latent heat flux to the atmosphere and more SST anomalies and negative (positive) GR (less) water availability to build precipitation anomalies. This relationship could indicate that systems. Additionally, RH negative (positive) positive (negative) SST anomalies are associ- anomalies tend to be associated with positive ated with a warmer (cooler) atmosphere layer (negative) WS anomalies (Fig. 7), WS could Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 S71 cdf cdf cdf cdf cdf cdf temperature trends are more likely significant Early period 1 Late period and mostly positive (Hidalgo et al., in prep.). 0.9 0.8 ACKNOWLEDGMENTS 0.7 This work was supported by the fol- 0.6 lowing CIMAR and CIGEFI, UCR grants: 0.5 808-B0-654 (FEES-CONARE), 808-A9-180, 0.4 808-A9-902, 808-B5-298, 805-A9-532 (CSU- 0.3 CA-ASDI), 805-B3-600, 805-B3-413 (CI), 5 10 15 20 805-B0-065, 805-B4-227, 805-B0-810. Thanks Hour to José L. Vargas and Alberto Salazar for all Fig. 11. Diurnal cycle of reference evapotranspiration for the logistic support during the expeditions. early (September 1, 1998 to August 31, 2001) and late Also to the scientists, rangers and crew par- (September 1, 2010 to August 31, 2013) periods. ticipants who collaborated with setting up the meteorological stations. more or less be associated with more or less evaporation and humidity transport away from RESUMEN the island. During the cold Niño 3 condition Estudios de la interacción atmósfera-océano en el of October 2007, negative P, AST, SST and Pacífico de Costa Rica son escasos. Para identificar los sis- RH anomalies were observed in concordance temas oceanográficos que pueden estar influyendo el clima with positive WS and GR anomalies (Expedi- cerca de la Isla del Coco (Corredor de Protección Marina tion one anomalies in Fig. 7). These results del Pacífico Tropical del Este), realizamos seis expedicio-nes científicas entre 2007 y 2012. Dos estaciones meteoro- agreed with the conceptual model of climate lógicas automáticas fueron instaladas cerca de las bahías system response at Isla del Coco to cold de Chatham y Wafer durante las expediciones. Entre los ENSO conditions, proposed by Quirós-Badilla datos se incluyeron registros del Instituto Meteorológico & Alfaro (2009). Nacional, el Proyecto de Climatología Global de Precipi- Although the island did not show much tación (GPCP por sus siglas en inglés) y la Reconstrucción Extendida de Temperatura Superficial del Mar (ERSST change in terms of precipitation (Fig. 8), it por sus siglas en inglés). El clima es típico del Pacífico should be noted that the GPCP data suggested Tropical del Este. Su estacionalidad está impulsada por la that Costa Rica and parts of Nicaragua, as well variabilidad en la precipitación asociada con la migración as northern Central America and Southern meridional de la Zona de Convergencia Intertropical. El Mexico experienced drier wet-season condi- ciclo anual de precipitación tiene dos picos en mayo y tions during the late period compared to the julio, un mínimo relativo entre ellos en junio, y un mínimo absoluto en febrero. La mayoría de la precipitación se early period. Also, during the dry-season the registra de abril a noviembre. La mayoría de los eventos drying pattern over Costa Rica and Nicara- tienen corta duración y baja intensidad. Una tendencia en gua was present. It should be noted that the temperatura superficial del mar (TSM) fue observada de region is influenced by multidecadal climatic enero 1854 a diciembre 2013, coherente con las observa- mechanisms (e.g. Enfield, & Mestas-Nuñez, ciones de calentamiento en la región. De 1998 a 2013 hubo cambios en las distribuciones de casi todos los parámetros 1999; Mestas-Nuñez, & Enfield, 1999) and meteorológicos. La combinación de estos factores resul- therefore interpreting trends based on differ- tó en tasas más altas de evapotranspiración a través del ences between short time periods must be done ciclo diario, especialmente durante la noche. Anomalías with caution. For example, Hidalgo (2013) positivas de precipitación (P) tienden a ser asociados con found that 1982-2005 trends in precipitation anomalías positivas de temperatura superficial del aire over Central America were inconsistent across (TSA) y de TSM, y con anomalías negativas de radiación global (RG). Anomalías negativas de P tienden a ser aso- different datasets. Precipitation trends (1970- ciadas con anomalías negativas de TSA, TSM y anomalías 1999) are in general non-significant, while air positivas de RG. Anomalías negativas de humedad relativa S72 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 ETo (mm/hour) (HR) tienden a ser asociadas con anomalías positivas de Coco (Cocos Island), Costa Rica / Recherches mari- velocidad del viento (VV), y el efecto de la VV es opuesto nes à l’Ile du Coco, Costa Rica. Revista de Biología para anomalías positivas de HR. Durante la condición fría Tropical, 56(Supplement 2), 217 p. de Niño 3 de octubre del 2007, anomalías negativas de P, Cortés, J. (2012a). Bibliografía anotada sobre organismos, TSA, TSM y HR fueron observadas en concordancia con ambientes y procesos marinos en Bahía Culebra, anomalías positivas de VV y RG, de acuerdo con el modelo Guanacaste, Costa Rica. Revista de Biología Tropi- conceptual de la respuesta del sistema climático en la Isla cal, 60(Supplement 2), 231-242. del Coco ante condiciones frías de ENOS. Cortés, J. (2012b). Bibliografía sobre investigaciones mari- Palabras clave: Isla del Coco, Costa Rica, Pacífico Tropi- nas, oceanográficas, geológicas y atmosféricas en el cal del Este, clima. Parque Nacional Isla del Coco y aguas adyacentes, Pacífico de Costa Rica. Revista de Biología Tropical, 60(Supplement 3), 363-392. REFERENCES Cortés, J. (Ed.) (2012c). Investigaciones marinas en el Parque Nacional Isla del Coco, Costa Rica / Marine Acuña-González, J., García-Céspedes, J., Gómez-Ramírez, Research at Isla del Coco National Park, Costa Rica. E., Vargas-Zamora, J. A., & Cortés, J. (2008). Pará- Revista de Biología Tropical, 60(Supplement 3), metros físico-químicos en aguas costeras de la Isla 394 p. del Coco, Costa Rica (2001-2007). Revista de Biolo- Cortés, J. (2014). Compilación y análisis de las investiga- gía Tropical, 56(Supplement 2), 49-56. ciones científicas sobre temas marinos y atmosféricos Adler, R. F., Huffman, G. J., Chang, A., Ferraro, R., Xie, en el Pacífico Norte de Costa Rica. Revista de Biolo- P., Janowiak, J., Rudolf, B., Schneider, U., Curtis, gía Tropical, 62(Supplement 4), 151-184. S., Bolvin, D., Gruber, A., Susskind, J., & Arkin, P. Cortés, J., Morales, A., Alfaro, E., Lizano, O., & Acuña, J. (2003). The Version 2 Global Precipitation Climato- (2010). Conocimiento y gestión de medios marinos logy Project (GPCP) Monthly Precipitation Analysis y coralinos del Área de Conservación Marina Isla (1979-Present). Journal of Hydrometeorology, 4, del Coco. (Manuales para el monitoreo. Cuadernillo 1147-1167. Informativo 2). San José, Costa Rica: SINAC, GEF- Alfaro, E. J. (2008). Ciclo diario y anual de variables PNUD y FFMAM. troposféricas y oceánicas en la Isla del Coco, Costa Enfield, D. B, & Mestas-Nuñez, A. M. (1999). Multiscale Rica. Revista de Biología Tropical, 56 (Supplement variabilities in global sea surface temperatures and 2), 19-29. their relationships with tropospheric climate patterns. Alfaro, E. J., Cortés, J., Alvarado, J. J., Jiménez, C., Journal of Climate, 12, 2719-2733. Sánchez-Noguera, C., Nivia, J., León, A., & Ruiz, Fernández, W. (1984). Comments on meteorological and E. (2012). Clima y temperatura sub-superfical del climatological observations on Coco Island. Revista mar en Bahía Culebra, Golfo de Papagayo, Costa Geofísica, 20, 9-19. Rica. Revista de Biología Tropical, 60(Supplement Fiedler, P. C., & Lavin-Peregrina, M. F. (2006). Introduc- 2), 159-171. tion: A review of eastern tropical Pacific oceanogra- Amador, J. A., Alfaro, E. J., Lizano, O. G., & Magaña, V. phy. Progress in Oceanography, 69, 94-100. O. (2006). Atmospheric forcing in the Eastern Tro- Hastenrath, S. (1991). Climate Dynamics of the Tro- pical Pacific: A review. Progress in Oceanography, pics. Dordrecht, Netherlands: Kluwer Academic 69, 101-142. Publishers. Bindoff, N. L., Stott, P. A., AchutaRao, K. M., Allen, M. Henderson, S., Rodríguez, A. M., & McManus, R. (2008). R., Gillett, N., Gutzler, D., Hansingo, K., Hegerl, G., A new future for marine conservation. Eastern Tropi- Hu, Y., Jain, S., Mokhov, I. I., Overland, J., Perlwitz, cal Pacific Seascape. (Technical Document). Virgi- J., Sebbari, R., & Zhang, X. (2013). Detection and nia, U.S.: Conservation International. Retrieved from attribution of climate change: from global to regional. http://www.conservation.org/ In T. F. Stocker, D. Qin, G. K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex Herrera, W. (1985). Consideraciones climáticas sobre la & P. M. Midgley (Eds.), Climate Change 2013: The Isla del Coco. In W. Herrera (Ed.), Clima de Costa physical science basis. Contribution of working Rica (pp. 40-44). San José, Costa Rica: EUNED. group I to the Fifth Assessment Report of the Intergo- Hidalgo, H. G. (2013). Tendencias hacia condiciones vernmental Panel on Climate Change (pp. 867-952). hidrológicas más secas en Centroamérica (1982- Cambridge, U.K. and New York, NY: Cambridge 2005). VII Congreso de la red Latinoamericana de University Press. Ciencias Ambientales, San Carlos, Costa Rica. Cortés, J. (Ed.) (2008). Investigaciones marinas en la Isla Huffman, G. J., Adler, R. F., Bolvin, D. T., Gu, G., Nel- del Coco, Costa Rica / Marine Research at Isla del kin, E. J., Bowman, K. P., Hong, Y., Stocker, E. F., Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016 S73 & Wolff, D. B. (2007). The TRMM Multi-satellite Morales-Ramírez, Á, Acuña-González, J., Lizano, O., precipitation analysis: Quasi-Global, Multi-Year, Alfaro, E., & Gómez, E. (2015). Rasgos oceanográ- combined-sensor precipitation estimates at fine scale. ficos en el Golfo Dulce, Pacífico de Costa Rica: una Journal of Hydrometeorology, 8, 38-55. revisión para la toma de decisiones en conservación marina. Revista de Biología Tropical, 63(Supplement Lavin-Peregrina, M. F., Fiedler, P. C., Amador-Buenrostro, 1): 131-160. A., Ballance, L., Farber-Lorda, J., & Mestas-Núñez, A. (2006). A review of the eastern tropical Pacific Pittier, H. F. (1898). Apuntamientos preliminares sobre la Isla del Coco, posesión costarricense en el Océano oceanography: Summary. Progress in Oceanography, Pacífico. In Reproducciones Científicas, una Expe- 69, 391-398. dición y Legislación de la Isla del Coco, 1963 (pp. Lizano, O., & Alfaro, E. (2004). Algunas características de 15-28). San José, Costa Rica: Instituto Geográfico de las corrientes marinas en Golfo de Nicoya. Revista de Costa Rica, Ministerio de Transportes. Biología Tropical, 52(Supplement 2), 77-94. Protti, M., González, V., Freymuller, J., & Doelger, S. Lizano, O. G., & Alfaro, E. (2014). Dinámica atmosférica y (2012). Isla del Coco, on Cocos Plate, converges with oceánica en algunos sitios del Área de Conservación Isla de San Andrés, on the Caribbean Plate, at 78mm/ Guanacaste (ACG), Costa Rica. Revista de Biología yr. Revista de Biología Tropical, 60(Supplement 3), Tropical, 62(Supplement 4), 17-31. 33 41. Quirós-Badilla, E., & Alfaro, E. (2009). Algunos aspectos Maldonado, T., & Alfaro, E. (2012). Revisión y compa- relacionados con la variabilidad climática en la Isla ración de escenarios de Cambio Climático para el del Coco, Costa Rica. Revista de Climatología, 9, Parque Nacional Isla del Coco, Costa Rica. Revista de 33-44. Biología Tropical, 60(Supplement 3), 83-112. Smith, T. M., Reynolds, R. W., Peterson, T. C., & Lawri- Mestas-Nuñez, A. M., & Enfield, D. B. (1999). Rotated more, J. (2008). Improvements to NOAA’s histori- global modes of non-ENSO sea surface temperature cal merged land-ocean surface temperature analysis variability. Journal of Climate, 12, 2734-2746. (1880-2006). Journal of Climate, 21, 2283-2296. S74 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 64 (Suppl. 1): S59-S74, February 2016