Seasonal Shift of the Diurnal Cycle of Rainfall Over Medellin's Valley, Central Andes of Colombia (1998–2005)

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 Aburrá Valley and the neighboring San Nicolás plateau (75.16 • W−6 • N and 75.66 • W−6.6 • N) which accounts for a land area of ∼4,000 km 2. 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.

Ground validation ofTRMM 3B43 V7precipitation estimates over Colombia. Part I: Monthly and seasonal timescales

“…It is also remarkable that the Andes, Caribbean and Pacific regions exhibit a bimodal annual cycle, with wet (dry) seasons in MAM and SON (JJA and DJF), while the Orinoco and Amazon regions exhibit unimodal annual cycles with a single dry season during DJF (Figure 2e–i). These spatiotemporal patterns can be explained by the meridional migration of the ITCZ which has been identified as the main modulating mechanism of intra‐annual variability over Colombia (Poveda, 2004; Poveda et al ., 2006), but also by the dynamics of diverse large‐scale phenomena that influence the moisture transport and precipitation regime of each region, mainly the three low‐level jets present in the country: (a) the Caribbean Low‐Level Jet (CLLJ) (Amador, 1998, 2008; Amador and Magana, 1999; Wang, 2007), which is active from northern South America to the Greater Antilles; (b) the Chocó Low‐Level Jet (Choco Jet) acting over the far eastern Pacific (Poveda and Mesa, 1999, 2000; Rueda and Poveda, 2006; Sakamoto et al ., 2011; Poveda et al ., 2014; Bedoya‐Soto et al ., 2019; Yepes et al ., 2019) and (c) the Corriente de los Andes Orientales (CAO) Low‐Level Jet or Eastern Andes Low‐Level Jet (Montoya et al ., 2001; Torrealba and Amador, 2010; Bedoya‐Soto et al ., 2019), also recently identified as Orinoco Low‐Level Jet (Jiménez‐Sánchez et al ., 2019), which constitutes the northernmost leg of the South American Low‐Level Jet (Berbery and Collini, 2000; Marengo et al ., 2004; Vera et al ., 2006). These mechanisms, together with complex soil–atmosphere interactions over the Andes and the Amazon and Orinoco River basins, contribute to the regional particularities that are evidenced in Figure 2 (Mejía et al ., 1999; Poveda, 2004).…”

“…Most of the rainfall in these areas is driven by orography and convection, which tends to be deeper where land–atmosphere interactions occur. For example, the warm rainfall in the Eastern and the Western piedmonts of the Andes is the result of the orographic uplift of the CLLJ and CAO, and the Choco low‐level jets, which bring the moisture from the Amazon Basin and the Pacific Ocean, respectively (Poveda et al ., 2014; Bedoya‐Soto et al ., 2019). Over these slopes, 3B43 V7 exhibits a significant underestimation (Figure 3m,r,u) that can be attributed to the well‐documented limitations of the PR to capture the rainfall rates of intense convective warm precipitation (Iguchi et al ., 2000; Dinku et al ., 2010b; Condom et al ., 2011; Rasmussen et al ., 2013; Mantas et al ., 2015; Erazo et al ., 2018).…”

“…Colombia, a country located in northwestern South America, exhibits such two challenging characteristics and, thus, provides a paradigmatic case study for the performance of satellite products. Precipitation in Colombia is the result of complex interactions between the dynamics of the Intertropical Convergence Zone (ITCZ), diverse low‐level jets, the Caribbean Sea, the Pacific and Atlantic Oceans, the Amazon and Orinoco River basins, land–atmosphere interactions and precipitation recycling (Bedoya‐Soto et al ., 2019), and the topography of the Andes (Poveda, 2004; Poveda et al ., 2006; Álvarez‐Villa et al ., 2011). As a consequence climate is very diverse, ranging from an extremely wet precipitation regime in the tropical rainforest of the Pacific coast (Poveda and Mesa, 2000) to a dry regime in the northern desert region of the country (Dinku et al ., 2010b).…”

Spatiotemporal dynamics of dengue in Colombia in relation to the combined effects of local climate and ENSO

“…A uni-modal annual cycle predominates in other regions, with maximum and minimum rainfall rates depending on position of the ITCZ, and the aforementioned low-level jets and land-surface feedbacks. On the other hand, Colombia exhibits a strong interannual climatic variability associated with ENSO, showing prolonged dry (wet) periods and above (below) normal temperatures during El Niño (La Niña) [76,80,82-89].…”

One‐minute integrated rainfall rate statistics from a rain gauge network in Colombia: accuracy of prediction methods

“…Aburra Valley: The valley is located in the centre of the department of Antioquia (around 6°N, 75.6°W), on the central chain of the Andes mountain range, with an average elevation of 1538 m. The city of Medellin and its metropolitan area are in the valley and represent the second-largest urban centre in Colombia, second only to the metropolitan area of the Country's capital, Bogota. As [1] presents in detail, precipitation on the valley is dominated by the influence of the inter-tropical convergence zone (ITCZ), which results in two rainy seasons per year (April-May and September-October), and by the dynamics of three low-level jets in the region namely CHOCO, Caribbean, and Corriente de los Llanos Orientales (CAO). The orography of the valley reflects in differences in the diurnal cycle of rainfall.…”