Climatology of extreme cold events in the central Peruvian Andes during austral summer: origin, types and teleconnections

Abstract

The climatological and large‐scale characteristics of the extreme cold events (ECEs) in the central Peruvian Andes (Mantaro basin (MB)) during austral summer (January–March) are examined using reanalysis, gridded and in situ surface minimum temperature (Tmin) data for the 1979–2010 period. To describe the influence of the Madden–Julian Oscillation (MJO) on ECEs in the MB, two ECE groups are defined on the basis of the sign of the outgoing long‐wave radiation (OLR) anomalies in the MJO band (30–100 days, 0–9 eastward) at 12.5°S, 75°W. Type‐1 ECEs occur during the suppressed convection phase of the MJO (OLR anomalies ≥+2 W/m2) while Type‐2 ECEs occur during the enhanced convection phase of the MJO (OLR anomalies ≤−2 W/m2). ECEs in the MB are associated with the advection of cold and dry air along the east of the Andes through equatorward propagation of extratropical Rossby wave trains (ERWTs). This cold advection weakens the Bolivian High–Nordeste Low (BH‐NL) system over South America (SA) at upper‐tropospheric levels. The MJO is an important driver of ECEs in the MB, favouring the cold advection along the Andes during specific MJO phases. Fifty‐nine per cent of Type‐1 ECE's and 86% of Type‐2 ECE's occur in MJO Phases 7‐2. Type‐1 and 2 ECEs feature a weakened BH over SA at upper‐tropospheric levels. For Type‐1, ERWTs emanate from southeastern Africa in MJO Phases 8‐1 while ERWTs are strengthened when crossing the subtropical southern Pacific Ocean during MJO Phases 2 and 7. With respect to Type‐2, MJO Phases 7‐2 feature circumpolar Rossby wave trains propagating toward SA. Ultimately, MJO Phases 7‐2 induce negative Tmin anomalies over MB, while MJO Phases 3‐6 induce positive Tmin anomalies. El Niño and La Niña strengthen negative Tmin anomalies over the MB during MJO Phases 7‐8 while they weaken positive Tmin anomalies over the MB during MJO Phases 3‐6.

Hydroclimate of the Andes Part II: Hydroclimate Variability and Sub-Continental Patterns

“…Over the north tropical Andes (north of 8 °S), the MJO is related to enhanced (reduced) amplitude of the diurnal cycle of precipitation during its westerly (easterly) phase (Poveda et al, 2005). Also, the MJO has been identified as a driver of extreme temperature and rainfall events in the south tropical Andes and the western Amazonia Sulca et al, 2018;Grimm, 2019;Mayta et al, 2019;Recalde-Coronel et al, 2020). The occurrence of eastward-propagating equatorially confined MJO events that do not evolve through a complete life cycle are associated with suppressed rainfall conditions over the tropical Andes (Mayta et al, 2019;Recalde-Coronel et al, 2020).…”

“…Over the south tropical Andes (between 8 °S and 27 °S), incursions of low-level southern winds from southern South America are related to the variability of the cloud cover in the Cordillera Real in Bolivia (Sicart et al, 2016). In addition, southerly incursions of cold and dry air along the eastern the Andes, low cloud cover, surface specific humidity, and soil moisture are key factors controlling the day-to-day variability of minimal temperature in the central Peruvian Andes (Saavedra and Takahashi, 2017;Sulca et al, 2018). During the austral summer, subseasonal rainfall variability over south tropical Andes is in part related to the variability of the South Atlantic Convergence Zone (SACZ) and the Bolivian High-Nordeste Low system, as discussed in Espinoza et al (2020) and Jones and Carvalho (2002).…”

High Impact Weather Events in the Andes

“…During these events 925-hPa southerly winds are intensified from 0 to 10 m s −1 and the 925-700 hPa lapse rates is low (−3 • C km −1 ). Cold surges, also known as Friajes or Surazos in Spanish (Friagems, in Portuguese), propagate equatorward reaching the Bolivian and southern Peruvian Amazon, causing sudden and severe drops in temperature, up to 10 • C in few hours, affecting people, livestock and crops (Marengo, 1983;Ronchail, 1989a,b;Marengo et al, 1997;Garreaud and Wallace, 1998;Pezza and Ambrizzi, 2005;Quispe, 2010;Sulca et al, 2018). Incursions of low-level cold southerly winds from southern South America are also associated with rainy episodes on the Amazon-Andes transition region (Chávez and Takahashi, 2017;Paccini et al, 2017), as well as formation of thick clouds in the Zongo glacier region in Bolivia (16 • S, 5,060 m a.s.l.…”

“…In the central Peruvian Andes, radiative frosts are a major hazard to agriculture. They are caused by low cloud cover, surface air humidity, and soil moisture (Saavedra and Takahashi, 2017), and tend to occur at night times and early morning of the dry and cold seasons (June-August) (Saavedra and Takahashi, 2017;Sulca et al, 2018). During the austral summer, extreme cold events in the Mantaro Valley (central Peruvian Andes, around 500-5,300 m a.s.l.)…”

A cold wave of winter 2021 in central South America: characteristics and impacts

“…Cold surges involve the incursion of cold and dry air masses from the southernmost part of the continent of South America toward low latitudes (e.g., Sulca et al 2018 ). A cold wave is a meteorological event generally characterized by a sharp drop of air temperature to extremely low values near the surface, a steep rise of pressure, and higher wind speed, associated with hazardous weather.…”