One-year measurements of surface heat budget on the ablation zone of Antizana Glacier 15, Ecuadorian Andes

International audience[1] Meteorological variables were recorded (14 March 2002 to 14 March 2003) at 4890 m above sea level (asl) on the Antizana Glacier 15 (0.71 km 2 ; 0°28 0 S, 78°09 0 W) in the tropical Andes of Ecuador (inner tropics). These variables were used to compute the annual cycle of the local surface energy balance (SEB). The four radiative fluxes were directly measured, and the turbulent fluxes were calculated using the bulk aerodynamic approach, calibrating the roughness length by direct sublimation measurements. The meteorological conditions are relatively homogeneous throughout the year (air temperature and air humidity). There is a slight seasonality in precipitation with a more humid period between February and June. During June-September, wind velocity shows high values and is responsible for intense turbulent fluxes that cause reduction of melting. Considering the SEB over the whole year, it is dominated by net radiation, and albedo variations govern melting. During the period under consideration the net shortwave radiation S (123 W m À2) and the sensible turbulent heat flux H (21 W m À2) were energy sources at the glacier surface, whereas the net long-wave radiation L (À39 W m À2) and the latent turbulent heat flux LE (À27 W m À2) represented heat sinks. Since the O°C isotherm-glacier intersection always oscillates through the ablation zone and considering that the phase of precipitation depends on temperature, temperature indirectly controls the albedo values and thus the melting rates. This control is of major interest in understanding glacier response to climate change in the Ecuadorian Andes, which is related to global warming and ENSO variability

Retroceso del glaciar del Carihuairazo y sus implicaciones en la comunidad de Cunucyacu

El retroceso de los glaciares es una realidad en toda la cordillera de los Andes, sobre todo en montañas de baja altitud. Uno de estos casos es la pérdida de la masa de hielo remanente en el Carihuairazo (Tungurahua, Ecuador), que en los últimos años ha experimentado un retroceso considerable. En esta investigación se intenta caracterizar el retroceso de este glaciar y su implicación en la comunidad más cercana (Cunucyacu) por medio de la aplicación de una metodología de múltiples fuentes que incluye la recopilación de aerofotografías del glaciar, datos de estaciones meteorológicas cercanas, uso de datos de reanálisis del clima global, entrevistas a miembros de la comunidad y a andinistas que trabajan y frecuentan la zona. Para caracterizar la evolución de la masa del glaciar aplicamos un modelo hidroglaciológico que usa como entrada datos de series meteorológicas y cuyos parámetros fueron calibrados con el registro fotográfico del contorno del glaciar. Como resultados se puede evidenciar una pérdida del glaciar para el 2021 equivalente al 99% de su superficie en 1956 (0.34 km2 ). El modelo logra simular la variación del área del glaciar durante 67 años, en donde se observa un decrecimiento continuo del glaciar a partir de 1978, con cortos periodos de recuperación y equilibrio, en donde la temperatura es la variable que mejor explica el retroceso del glaciar. El modelo no logra considerar el efecto de factores externos como el caso de la erupción del volcán Tungurahua que podría favorecer el retroceso del glaciar. El glaciar Carihuairazo se encuentra en una situación de inevitable desaparición y revela las vulnerabilidades de las comunidades que se enfrentan a este fenómeno como consecuencia del cambio climático.//The retreat of glaciers is a reality throughout the Andes Mountain range, especially in low-altitude mountains. One of these cases is the loss of the remaining ice mass in Carihuairazo (Tungurahua, Ecuador), which in recent years has experienced a considerable retreat. This research aims to characterize the retreat of this glacier and its implications for the nearby community (Cunucyacu) through the application of a multi-source methodology, which includes the collection of glacier aerial photographs, data from nearby meteorological stations, the use of global climate reanalysis data, interviews with community members, and mountaineers who work and frequent the area. To characterize the glacier’s mass evolution, a hydroglaciological model was applied, using input data from meteorological series, and its parameters were calibrated with the photographic record of the glacier’s outline. The results show a glacier loss of 99% of its surface in 1956 (0.34 km2 ) by 2021. The model successfully simulates the glacier area variation over 67 years, revealing a continuous decrease since 1978, with short periods of recovery and equilibrium, where temperature is the variable that best explains the glacier’s retreat. However, the model fails to consider the effect of external factors, such as the eruption of the Tungurahua volcano that could enhance the glacier retreat. The Carihuairazo glacier is in a situation of inevitable disappearance, highlighting the vulnerabilities of communities facing this phenomenon as a consequence of climate change

Review article of the current state of glaciers in the tropical Andes: a multi-century perspective on glacier evolution and climate change

The aim of this paper is to provide the community with a comprehensive overview of the studies of glaciers in the tropical Andes conducted in recent decades leading to the current status of the glaciers in the context of climate change. In terms of changes in surface area and length, we show that the glacier retreat in the tropical Andes over the last three decades is unprecedented since the maximum extension of the LIA (mid 17th–early 18th century). In terms of changes in mass balance, although there have been some sporadic gains on several glaciers, we show that the trend has been quite negative over the past 50 yr, with a mean mass balance deficit for glaciers in the tropical Andes that is slightly more negative than the computed global average. A break point in the trend appeared in the late 1970s with mean annual mass balance per year decreasing from −0.2m w.e. in the period 1964–1975 to −0.76m w.e. in the period 1976–2010. In addition, even if glaciers are currently retreating everywhere in the tropical Andes, it should be noted that as a percentage, this is much more pronounced on small glaciers at low altitudes that do not have a permanent accumulation zone, and which could disappear in the coming years/decades. Monthly mass balance measurements performed in Bolivia, Ecuador and Colombia showed that variability of the surface temperature of the Pacific Ocean is the main factor governing variability of the mass balance variability at the interannual to decadal time scale. Precipitation did not display a significant trend in the tropical Andes in the 20th century, and consequently cannot explain the glacier recession. On the other hand, temperature increased at a significant rate of 0.10◦Cdecade−1 in the last 70 yr. The higher frequency of El Nin ̃o events and changes in its spatial and temporal occurrence since the late 1970s together with a warming troposphere over the tropical Andes may thus explain much of the recent dramatic shrinkage of glaciers in this part of the world

Adaptive PI Controller Based on a Reinforcement Learning Algorithm for Speed Control of a DC Motor

Automated industrial processes require a controller to obtain an output signal similar to the reference indicated by the user. There are controllers such as PIDs, which are efficient if the system does not change its initial conditions. However, if this is not the case, the controller must be retuned, affecting production times. In this work, an adaptive PID controller is developed for a DC motor speed plant using an artificial intelligence algorithm based on reinforcement learning. This algorithm uses an actor–critic agent, where its objective is to optimize the actor’s policy and train a critic for rewards. This will generate the appropriate gains without the need to know the system. The Deep Deterministic Policy Gradient with Twin Delayed (DDPG TD3) was used, with a network composed of 300 neurons for the agent’s learning. Finally, the performance of the obtained controller is compared with a classical control one using a cost function