Abstract
The spatiotemporal variability of precipitation in regions of complex mountainous terrains constitutes one of the most challenging research topics of geosciences. This paper explores hourly precipitation data from a set of 25 stations spanning the period 1998 to 2005 within northwestern Colombia, in the Aburra Valley and the neighboring San Nicolas plateau (75.16W-6N and 75.66W-6.6N) which accounts for a land area of approximately 4000 km2. Our aim is to identify the main features of the diurnal cycle of precipitation over this complex terrain. We found that the average diurnal cycle of rainfall in the study region is bimodal at regional scale although it results from the superposition of two unimodal diurnal cycles shifting its phase throughout the seasons of the year. From October to April, average diurnal rainfall peaks in the afternoon hours (13:00-16:00 LST) but from May to September, the phase of the diurnal cycle changes to midnight hours (22:00-02:00 LST). Three low-level jets (LLJs), namely Caribbean, CHOCO, and the so-called Corriente de los Andes Orientales (CAO), are relevant to explain the seasonal shift of the diurnal cycle given their modulation of the seasonal variation of moisture sources and transport over this region. During June-July-August, moisture from afternoon evaporation processes at the bottom of the inter-Andean Magdalena Valley, located at the east of the study region, is transported by anabatic and easterly trade winds and contribute to explain the midnight and early morning peak. The life cycle of convective processes influences the orographic nature of rainfall distribution and timing in the region since deep convective cores are related with the afternoon peak, whereas wide convective cores with the early morning peak.
Highlights
Colombia is located in the northwestern corner of Tropical South America and presents some particular geomorphologic and hydro-climate features including: (i) steep slopes across the three Cordilleras of the Andes crossing from southwest to northeast, (ii) seasonal activity of three atmospheric low-level jets, (iii) hydro-climate systems of the Amazon and Orinoco River basins, (iv) synoptic-scale atmospheric patterns associated with the tropical Pacific and AtlanticSeasonal Shift of the Diurnal CycleOceans and the Caribbean Sea, and (v) land-atmosphere feedback processes
We study the linkages between the diurnal cycles of rainfall along a longitudinal transect covering two neighboring regions located on the Central range of the Colombian Andes: the San Nicolás Plateau and the Aburrá Valley, containing the city of Medellín
Two periods of higher rainfall are seen during April and May (A-M) and from September to October (S-O), and two periods of lower rainfall during D-J-F and JJ-A, owing to the meridional displacement of the Intertropical Convergence Zone (ITCZ) and other physical mechanisms
Summary
Colombia is located in the northwestern corner of Tropical South America and presents some particular geomorphologic and hydro-climate features including: (i) steep slopes across the three Cordilleras (ranges) of the Andes crossing from southwest to northeast, (ii) seasonal activity of three atmospheric low-level jets, (iii) hydro-climate systems of the Amazon and Orinoco River basins, (iv) synoptic-scale atmospheric patterns associated with the tropical Pacific and AtlanticSeasonal Shift of the Diurnal CycleOceans and the Caribbean Sea, and (v) land-atmosphere feedback processes. Diverse studies have tackled the spatio-temporal variability of rainfall over the Colombian Andes (Schmidt, 1952; Trojer, 1959; López and Howell, 1967; Snow, 1976; Oster, 1979; Martínez, 1993; Poveda and Mesa, 1997; Mejía et al, 1999; León and Narávez, 2001; Poveda et al, 2001, 2005, 2007, 2011; Mapes et al, 2003a; Poveda, 2004, 2011; Zuluaga and Poveda, 2004; Pabón and Dorado, 2008; Hurtado and Poveda, 2009; Alvarez-Villa et al, 2011; Hurtado-Montoya and Mesa-Sánchez, 2014; Poveda and Salas, 2015; Salas and Poveda, 2015; Jaramillo et al, 2017; Bedoya-Soto et al, 2018) In spite of such large body of literature, the dynamical and thermodynamical processes associated with rainfall over the Andes of Colombia are largely unknown, more so at high spatial and temporal resolutions. The mentioned study did not find a clearcut relation between extremes of the diurnal cycle with elevation, branch, and aspect on the Andes, except for some small regions within the intra-Andean valleys
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