The Diurnal Cycle of Precipitation in the Tropical Andes of Colombia

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.

Role of moisture transport for Central American precipitation

“…the CLLJ) it is then transported to Central America. The intensification of moisture transport from this source between May and September is in agreement with the reduction in rainfall for several locations in northern Colombia (Poveda et al, 2005). Recent studies make this northern South AmericaCentral America link clear; Arias et al (2015) showed that La Niña enhances the moisture transport to northern South America hence decreasing availability for Central American supply.…”

The Andes climate and weather

“…This large precipitation is due to enhanced orographic rainfall and the permanent drizzle from orographic clouds (Emck, 2007). The presence of the Cauca and Magdalena valleys along the Colombian Andes also causes a very complex distribution of rainfall with alternating bands of humid and hyper-humid conditions (Lopez and Howell, 1967;Poveda et al, 2005). North of 2 • S, the Andes also experience two rainy seasons, around late fall and spring, in connection with the meridional displacement of the Intertropical Convergence Zone (ITCZ) over the eastern Pacific.…”

Impacts of different ENSO flavors and tropical Pacific convection variability (ITCZ, SPCZ) on austral summer rainfall in South America, with a focus on Peru

“…The ITCZ only moves into the South American continent during the extreme El Niño events (Takahashi and Battisti, 2007). So far, most of the observational and modelling studies focused on the impacts of the meridional displacement of the ITCZ on rainfall of NEB (Hastenrath and Heller, 1977;Moura and Shukla, 1981;Hastenrath and Greischar, 1993), the Colombian Andes (Poveda et al, 2005) and the northern coast of Peru (Philander, 1990). However, none of these studies assess the impacts of the central Pacific ITCZ by itself on the inter-annual variability of the precipitation of South America (SA).…”