A record‐setting temperature of 17.5°C occurred on 24 March 2015 at the Esperanza station located near the northern tip of the Antarctic Peninsula (AP). We studied the event using surface station data, satellite imagery, reanalysis data, and numerical simulations. The Moderate Resolution Imaging Spectroradiometer Antarctic Ice Shelf Image Archive provides clear evidence for disintegration and advection of sea ice, as well as the formation of melt ponds on the ice sheet surface at the base of the AP mountain range. A deep low‐pressure center over the Amundsen‐Bellingshausen Sea and a blocking ridge over the southeast Pacific provided favorable conditions for the development of an atmospheric river with a northwest‐southeast orientation, directing warm and moist air toward the AP, and triggering a widespread foehn episode. A control simulation using a regional climate model shows the existence of local topographically induced warming along the northern tip of the AP (∼60% of the full temperature signal) and the central part of the eastern AP (>90% of the full temperature signal) with respect to a simulation without topography. These modeling results suggest that more than half of the warming experienced at Esperanza can be attributed to the foehn effect (a local process), rather than to the large‐scale advection of warm air from the midlatitudes. Nevertheless, the local foehn effect also has a large‐scale advection component, since the atmospheric river provides water vapor for orographic precipitation enhancement and latent heat release, which makes it difficult to completely disentangle the role of local versus large‐scale processes in explaining the extreme event.

The ionospheric responses to the total solar eclipse on 2 July 2019 over low latitudes in southern South America are presented. Ionosonde observations were used within the totality path at La Serena (LS: 29.9°S, 71.3°W) and at Tucumán (TU: 26.9°S, 65.4°W) and Jicamarca (JI: 12.0°S, 76.8°W), with 85% and 52% obscuration, respectively. Total electron content (TEC) estimations over the South American continent were analyzed. The ionospheric impact of the eclipse was simulated using the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) at the Instituto Nacional de Pesquisas Espaciais (INPE). The significant variability of the diurnal variations of the various ionospheric characteristics over equatorial and low latitudes on geomagnetically quiet days makes it difficult to unambiguously determine the ionospheric responses to the eclipse. Nonetheless, some specific issues can be derived, mainly using simulation results. The E and F1 layer critical frequencies and densities below 200 km are found to consistently depend on decreasing solar radiation. However, the F1 layer stratification observed at both TU and LS cannot be related to the eclipse or other processes. The F2 layer does not follow the changes in direct solar radiation during the eclipse. The SUPIM-INPE-modeled F region critical frequency and TEC are overestimated before the eclipse at LS and particularly at TU. However, these overestimations are within the observed large day-today variability. When an artificial prereversal enhancement is added, the simulations during the eclipse better reproduce the observations at JI, are qualitatively better for LS, and are out of phase for TU. The simulations are consistent with conjugate location effects.

Abstract. The dynamics of global Pc5 waves during the magnetic storms on 29-31 October 2003 are considered using data from the trans-American and trans-Scandinavian networks of magnetometers in the morning and post-noon magnetic local time (MLT) sectors. We study the latitudinal distribution of Pc5 wave spectral characteristics to determine how deep into the magnetosphere these Pc5 waves can extend at different flanks of the magnetosphere. The wave energy transmission mechanisms are different during 29-30 October and 31 October wave events. Further, we examine whether the self-excited Kelvin-Helmholtz instability is sufficient as an excitation mechanism for the global Pc5 waves. We suggest that on 31 October a magnetospheric magnetohydrodynamic (MHD) waveguide was excited, and the rigid regime of its excitation was triggered by enhancements of the solar wind density. The described features of Pc5 wave activity during recovery phase of strong magnetic storm are to be taken into account during the modeling of the relativistic electron energization by ultra-low-frequency (ULF) waves.Keywords. Magnetospheric physics (MHD waves and instabilities; storms and substorms) -space plasma physics (kinetic and MHD theory)

Urban pollution can often impact surrounding, non-urban regions, through advection and dispersal of pollutants by the prevailing winds. Urban regions located upstream of high mountains, such as the Andes, can potentially impact the cryosphere by deposition of particles onto the surface of the snowpack and glaciers.Santiago, the capital of Chile, has more than 6 million inhabitants and regularly experiences episodes of severe pollution, particularly during the austral winter. Some studies have hypothesized that particle pollution from Santiago can reach the cryosphere downwind of the city, but the scarcity of measurements made high in the mountains prevents the validation of mesoscale models so the proof of actual impact remains elusive. A research project was designed to provide some insight into this question. The Pollution Impact on Snow in the Cordillera -Experiments and Simulations (PISCES) project was carried out in 2014 and includes both observational and modeling components. A five-week field campaign was conducted at the end of winter, at an elevated site in a mountain valley, 65 km to the southeast of the center of Santiago, to characterize some aspects of particulate pollution.During synoptic conditions that result in clear days at the site, the mesoscale mountain-valley circulation is effective in transporting pollutants upwards during the day, leading to diluted particle concentrations beyond the summits of the highest peaks. Cloudy days with reduced up-valley circulation do not show increased concentrations associated with transport. Back trajectories indicate that air masses reaching the site during the field campaign are seldom influenced by pollution from Santiago.

Abstract. Special forecasts from the Global Forecast System (GFS) model were used in this study to evaluate how the intensification process in a tropical cyclone is represented in this model. Several tropical cyclones that developed in 2005 were analyzed in terms of the storm-scale circulation rather than more traditional measures such as maximum wind or minimum central pressure. The primary balance governing the circulation in the planetary boundary layer is between the convergence of environmental vorticity, which tends to spin up the storm, and surface friction, which tends to spin it down. In addition, we employ recently developed ideas about the relationship between precipitation and the saturation fraction of the environment to understand the factors controlling mass, and hence vorticity convergence. The budget of moist entropy is central to this analysis. Two well-known governing factors for cyclone intensification emerge from this study; surface moist entropy fluxes, dependent in the model on sea surface temperature and cyclone-generated surface winds, and ventilation of the system by dry environmental air. Quantitative expressions for the role of these factors in cyclone intensification are presented in this paper.