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Abstract
The ChocoJet Experiment (CHOCO-JEX) is an interinstitutional research program developed by the Universidad Nacional de Colombia, the General Maritime Directorate of the Ministry of National Defense of Colombia, the Colombian Air Force, and the Desert Research Institute. The main goal of CHOCO-JEX is to characterize the vertical structure of the low-level Chocó jet (ChocoJet) through observations and modeling. Thus, four 7-day intensive observation periods (IOPs) took place during different seasons in 2016, two over land and two over the far eastern Pacific off the coast of Colombia, including the deployment of upper-air soundings four times per day to monitor the predominant diurnal cycle and the synoptic and seasonal variability. Preliminary results show deeper westerly moisture flow and a stronger diurnal cycle over land than over ocean. IOP4 provides the first observational evidence of the southwesterly ChocoJet with mean winds of 5 m s–1. Diurnal cycles of zonal wind are coherent with mountain–valley and sea–land breezes at low levels and the easterly flow is predominant at midlevels. Potential temperature anomalies appear to be related to gravity waves that modulate the diurnal cycle of precipitation in the region.
Abstract
The ChocoJet Experiment (CHOCO-JEX) is an interinstitutional research program developed by the Universidad Nacional de Colombia, the General Maritime Directorate of the Ministry of National Defense of Colombia, the Colombian Air Force, and the Desert Research Institute. The main goal of CHOCO-JEX is to characterize the vertical structure of the low-level Chocó jet (ChocoJet) through observations and modeling. Thus, four 7-day intensive observation periods (IOPs) took place during different seasons in 2016, two over land and two over the far eastern Pacific off the coast of Colombia, including the deployment of upper-air soundings four times per day to monitor the predominant diurnal cycle and the synoptic and seasonal variability. Preliminary results show deeper westerly moisture flow and a stronger diurnal cycle over land than over ocean. IOP4 provides the first observational evidence of the southwesterly ChocoJet with mean winds of 5 m s–1. Diurnal cycles of zonal wind are coherent with mountain–valley and sea–land breezes at low levels and the easterly flow is predominant at midlevels. Potential temperature anomalies appear to be related to gravity waves that modulate the diurnal cycle of precipitation in the region.
Abstract
Using hourly records from 51 rain gauges, spanning between 22 and 28 yr, the authors study the diurnal cycle of precipitation over the tropical Andes of Colombia. Analyses are developed for the seasonal march of the diurnal cycle and its interannual variability during the two phases of El Niño–Southern Oscillation (ENSO). Also, the diurnal cycle is analyzed at intra-annual time scales, associated with the westerly and easterly phases of the Madden–Julian oscillation, as well as higher-frequency variability (<10 days), mainly associated with tropical easterly wave activity during ENSO contrasting years. Five major general patterns are identified: (i) precipitation exhibits clear-cut diurnal (24 h) and semidiurnal (12 h) cycles; (ii) the minimum of daily precipitation is found during the morning hours (0900–1100 LST) regardless of season or location; (iii) a predominant afternoon peak is found over northeastern and western Colombia; (iv) over the western flank of the central Andes, precipitation maxima occur either near midnight, or during the afternoon, or both; and (v) a maximum of precipitation prevails near midnight amongst stations located on the eastern flank of the central Cordillera. The timing of diurnal maxima is highly variable in space for a fixed time, although a few coherent regions are found in small groups of rain gauges within the Cauca and Magdalena River valleys. Overall, the identified strong seasonal variability in the timing of rainfall maxima appears to exhibit no relationship with elevation on the Andes. The effects of both phases of ENSO are highly consistent spatially, as the amplitude of hourly and daily precipitation diminishes (increases) during El Niño (La Niña), but the phase remains unaltered for the entire dataset. We also found a generalized increase (decrease) in hourly and daily rainfall rates during the westerly (easterly) phase of the Madden–Julian oscillation, and a diminished (increased) high-frequency activity in July–October and February–April during El Niño (La Niña) years, associated, among others, with lower (higher) tropical easterly wave (4–6 day) activity over the Caribbean.
Abstract
Using hourly records from 51 rain gauges, spanning between 22 and 28 yr, the authors study the diurnal cycle of precipitation over the tropical Andes of Colombia. Analyses are developed for the seasonal march of the diurnal cycle and its interannual variability during the two phases of El Niño–Southern Oscillation (ENSO). Also, the diurnal cycle is analyzed at intra-annual time scales, associated with the westerly and easterly phases of the Madden–Julian oscillation, as well as higher-frequency variability (<10 days), mainly associated with tropical easterly wave activity during ENSO contrasting years. Five major general patterns are identified: (i) precipitation exhibits clear-cut diurnal (24 h) and semidiurnal (12 h) cycles; (ii) the minimum of daily precipitation is found during the morning hours (0900–1100 LST) regardless of season or location; (iii) a predominant afternoon peak is found over northeastern and western Colombia; (iv) over the western flank of the central Andes, precipitation maxima occur either near midnight, or during the afternoon, or both; and (v) a maximum of precipitation prevails near midnight amongst stations located on the eastern flank of the central Cordillera. The timing of diurnal maxima is highly variable in space for a fixed time, although a few coherent regions are found in small groups of rain gauges within the Cauca and Magdalena River valleys. Overall, the identified strong seasonal variability in the timing of rainfall maxima appears to exhibit no relationship with elevation on the Andes. The effects of both phases of ENSO are highly consistent spatially, as the amplitude of hourly and daily precipitation diminishes (increases) during El Niño (La Niña), but the phase remains unaltered for the entire dataset. We also found a generalized increase (decrease) in hourly and daily rainfall rates during the westerly (easterly) phase of the Madden–Julian oscillation, and a diminished (increased) high-frequency activity in July–October and February–April during El Niño (La Niña) years, associated, among others, with lower (higher) tropical easterly wave (4–6 day) activity over the Caribbean.
