From 18 to 27 March 2015, northern, central, and southern Chile experienced a series of extreme hydrometeorological events. First, the highest surface air temperature ever recorded in Santiago (with reliable records dating to 1877), 36.8°C at Quinta Normal, was measured at 15:47 local time on 20 March 2015. Immediately following this high heat event, an extreme precipitation event, with damaging streamflows from precipitation totals greater than 45 mm, occurred in the semiarid and hyperarid Atacama regions. Finally, concurrent with the heavy precipitation event, extremely warm temperatures were recorded throughout southern Chile. These events were examined from a synoptic perspective with the goal of identifying forcing mechanisms and potential interaction between each analysis which provides operational context by which to identify and predict similar events in the future. Primary findings were as follows: (1) record warm temperatures in central Chile resulted from anomalous lower troposphere ridging and easterly downslope flow, both of which developed in response to an anomalous midtroposphere ridge‐trough pattern; (2) a cutoff low with anomalous heights near one standard deviation below normal slowly moved east and was steered ashore near 25°S by circulation around a very strong ridge (anomalies more than 3 standard deviations above normal) centered near 60°S; (3) anomalously high precipitable water content (20 mm above climatological norms) over the Peruvian Bight region was advected southward and eastward ahead of the cutoff low by low‐level northwesterly flow, greatly enhancing observed precipitation over northern Chile.
During the last four decades, the sea level pressure has been decreasing over the Amundsen-Bellingshausen Sea (ABS) region and increasing between 30-40°S from New Zealand to Chile, thus forming a pressure trend dipole across the South Pacific. The trends are strongest in austral winter and have influenced the climate of West Antarctica and South America. The pressure trends have been attributed to decadal variability in the tropics, expansion of the Hadley cell and an associated positive trend of the Southern Annular Mode, but these mechanisms explain only about half of the pressure trend dipole intensity. Experiments conducted with two atmospheric models indicate that upper ocean warming over the subtropical southwest Pacific (SSWP), termed the Southern Blob, accounts for about half of the negative pressure trend in the ABS region and nearly all the ridging /drying over the eastern subtropical South Pacific, thus contributing to the central Chile megadrought. The SSWP warming intensifies the pressure trend dipole through warming the troposphere across the sub-tropical South Pacific and shifting the mid-latitude storm track poleward into the ABS. Multi-decadal periods of strong SSWP warming also appears in fully coupled pre-industrial simulations, associated with a pressure trend dipole and reduction in rainfall over the central tropical Pacific, thus suggesting a natural origin of the Southern Blob and its teleconnection. However, the current warming rate exceeds the range of natural variability, implying a likely additional anthropogenic contribution.
The 2016/17 wildfire season in Chile was the worst on record, burning more than 600,000 ha. While wildfires are an important natural process in some areas of Chile, supporting its diverse ecosystems, wildfires are also one of the biggest threats to Chile’s unique biodiversity and its timber and wine industries. They also pose a danger to human life and property because of the sharp wildland–urban interface that exists in many Chilean towns and cities. Wildfires are, however, difficult to predict because of the combination of physical (meteorology, vegetation, and fuel condition) and human (population density and awareness level) factors. Most Chilean wildfires are started because of accidental ignition by humans. This accidental ignition could be minimized if an effective wildfire warning system alerted the population to the heightened danger of wildfires in certain locations and meteorological conditions. Here, we demonstrate the design of a novel probabilistic wildfire prediction system. The system uses ensemble forecast meteorological data together with a long time series of fire products derived from Earth observation to predict not only fire occurrence but also how intense wildfires could be. The system provides wildfire risk estimation and associated uncertainty for up to six days in advance and communicates it to a variety of end users. The advantage of this probabilistic wildfire warning system over deterministic systems is that it allows users to assess the confidence of a forecast and thus make more informed decisions regarding resource allocation and forest management. The approach used in this study could easily be adapted to communicate other probabilistic forecasts of natural hazards.
No abstract
During June 2022 surface air temperatures across most of Europe were above the 1991-2020 average and daily maximum temperatures reached over 40 ºC over southern Europe (according to Copernicus.eu). Unusually high temperatures were also reached in Germany, where heat waves took place with over 35 ºC. In the Jülich Observatory for Cloud Evolution (JOYCE), these extreme temperature and humidity conditions were registered. JOYCE combines a rather unique set of ground-based remote sensing instruments that provide information about Boundary Layer thermal structure. The present investigation utilizes some of those measurements to diagnose total mean flux of heat and moisture within the Boundary Layer. In order to analyze the daily evolution of these fluxes during a heat wave, we utilize measurements of temperature and humidity from an Atmospheric Emitted Radiance Interferometer (AERI) and plot them in the mixing diagram approach, i.e.,  in an energy space (Lq versus , where L is the latent heat of vaporization and is the specific heat). Additionally, we quantify, in a 2D vector representation, the contributions of surface, advection and entrainment fluxes to the total mean flux. Estimates of horizontal temperature and humidity advection are obtained from measurements of the 30º elevation scan of a Microwave Radiometer (MWR) and from wind velocities measured by a Doppler Lidar. Additionally, surface flux measurements from the Integrated Carbon Observation System (ICOS) in a near by station in Selhausen are utilized to quantify the contribution of these surface fluxes in the mixing diagram. The total mean flux shows a daytime evolution with both sensible and latent heat components observed in days before the heat wave; whereas a high sensible heat flux dominates during the heat wave and the advective contribution becomes more important when the heat wave ends. We discuss the daily evolution of these fluxes, as well as the implementation of the mixing diagram approach for their study utilizing measured quantities. The present investigation can shed light on the Land-Atmosphere interaction and the closure of the surface energy and water budgets. Furthermore, understanding how the surface conditions can affect the atmospheric variables is valuable for a better characterization, and subsequent prediction, of extreme events such as heat waves in a warming climate.
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