Global association of aerosol with flash density of intense lightning

A global scale study of the association between aerosol loading and lightning production was conducted, using a full year’s data for 2012 (as well as seasonal data) of the cloud-to-ground lightning record from the world wide lightning location network and aerosol optical depth measured by MODIS. 70% of all grid squares examined and 94% of the statistically significant ones had higher flash densities under polluted conditions than the clean ones. This trend is evident for large continental regions in North, Central and South America, Europe, southern Africa and north-east Australia. A detailed examination of the link to the meteorology was performed for four continental regions: the Amazon, North America, southern Africa and the Maritime Continent. The findings showed a similar trend under different meteorological conditions (defined by subsets of specified CAPE values and pressure velocity at 400 hPa). The results of this study suggest a route to association between aerosol loading and lightning-production rates in thunderclouds

Observational Evidence of the Transition from Shallow to Deep Convection in the Western Caribbean Trade Winds

The present study aims to determine the factors influencing the transition from shallow to deep convection in the trade winds region using an observational approach, with emphasis in the Yucatan Peninsula in eastern Mexico. The methodology is based on a discrimination of two regimes of convection: a shallow cumulus regime, usually with little or no precipitation associated, and an afternoon deep convection regime, with large amounts of precipitation, preceded by a short period of shallow convection. Then, composites of meteorological fields at surface and several vertical levels, for each of the two convection regimes, are compared to infer which meteorological factors are involved in the development of deep convection in this region. Also, the relationship between meteorological variables and selected regime-transition parameters is evaluated only for deep convection regime days. Results indicate the importance of dynamic factors, such as the meridional wind component, in the transition from shallow to deep convection. As expected, thermodynamic variables, such as the low-level specific humidity in the shallow cumulus layer, also contribute to the regime transition. The presence of a southerly component of wind at low- to mid-levels during the early morning in deep convection days provides the shallow cumulus with a more favorable environment so that transition can occur, since abundant moisture from the Caribbean is supplied through this prevailing southern wind. The results can be relevant for reducing uncertainties regarding some important parameters in global and regional models, which could lead to improved simulations of the transition from shallow to deep convection and precipitation

Spatio-temporal distribution of burned areas by ecoregions in Mexico and Central America

<p>Fire activity in Mexico and Central America, and its associated emissions, has impacts across multiple scales. On the local-to-regional scale, fire activity impacts land use, productivity, and biodiversity. On the regional-to-global scale, fire activity impacts hydrological, biogeochemical, and atmospheric processes. A consistent, reliable, large-scale characterization of the spatial and temporal distribution of fire burned area is required to assess its environmental impacts and to support natural resources’ management. The spatial and temporal distributions of fire burned areas in ecoregions of Mexico and Central America are evaluated in this study for the period 2001–2014, using the satellite Moderate Resolution Imaging Spectroradiometer (MODIS) MCD45 Burned Area data set. The methodology combines the 500 m burned area product with a MODIS land cover product and a map of North American land cover to calculate the spatiotemporal variability of fire activity as a function of land-use type.</p> <p>The total burned area over Mexico and Central America over the period 2001–2014 was found to be 614,243.5 km², but with significant interannual variability over the 14 years included in the study. Indeed, the minimum burned area over the period was 9892.25 km² in 2014 and the maximum was 37,669.50 km² in 2011, a fourfold increase. Burned areas were found to be concentrated in northern Mexico and on the Pacific coast, mainly from October to June. Agricultural burned areas accounted for 37% and 43% of total detected burns in Mexico and Central America, respectively. The largest extent of burned surface occurs in May for most land-cover types. The maximum density of burned areas occurred in the <i>tropical dry forests</i> ecoregion during the dry season. Both in Mexico and Central America, burned area anomalies have significant anti-correlation with precipitation anomalies.</p

Regional climate of the subtropical central Andes using high-resolution CMIP5 models—part I: past performance (1980–2005)

This study assesses the performance of 15 high resolution global climate models (GCMs) over the complex orographic region of the subtropical central Andes from available simulations of the Fifth Coupled Model Intercomparison Project (CMIP5). The simulated past climate (1980–2005) was compared against the Climate Research Unit (CRU) dataset and the ERA-Interim reanalysis, considered as reference datasets, to evaluate regional and seasonal surface temperature and precipitation, as well as sea level pressure and circulation. A good agreement was found between the simulations and the reference datasets for winter precipitation and for temperature over both seasons. Whilst all models correctly reproduce the annual cycle of precipitation, some of them overestimate winter totals. ERA-Interim does not adequately represent summer precipitation over the region, and some of the models analyzed also show the same deficiency. All models correctly reproduce the northward migration of the South Pacific subtropical high during winter, although some of them underestimate the maximum central pressure. During summer, most models fail to show the low level north–south flow parallel to the eastern foothills of the Andes, a feature known as the Low Level Jet. Further analysis of the results of the simulations led to the selection of a sub-set of five CMIP5 GCMs to construct a reduced ensemble. This reduced ensemble is a better representation than the multi-model mean of the 15 GCMs of the past climate at this region and would be recommended for future studies.Fil: Zazulie, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Rusticucci, Matilde Monica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Raga, Graciela B.. Universidad Nacional Autónoma de México; Méxic

Regional climate of the Subtropical Central Andes using high-resolution CMIP5 models. Part II: future projections for the twenty-first century

In Part I of our study (Zazulie et al. Clim Dyn, 2017, hereafter Z17) we analyzed the ability of a subset of fifteen high-resolution global climate models (GCMs) from the Coupled Model Intercomparison Project phase 5 to reproduce the past climate of the Subtropical Central Andes (SCA) of Argentina and Chile. A subset of only five GCMs was shown to reproduce well the past climate (1980–2005), for austral summer and winter. In this study we analyze future climate projections for the twenty-first century over this complex orography region using those five GCMs. We evaluate the projections under two of the representative concentration pathways considered as future scenarios: RCP4.5 and RCP8.5. Future projections indicate warming during the twenty-first century over the SCA region, especially pronounced over the mountains. Projections of warming at high elevations in the SCA depend on altitude, and are larger than the projected global mean warming. This phenomenon is expected to strengthen by the end of the century under the high-emission scenario. Increases in winter temperatures of up to 2.5 °C, relative to 1980–2005, are projected by 2040–2065, while a 5 °C warming is expected at the highest elevations by 2075–2100. Such a large monthly-mean warming during winter would most likely result in snowpack melting by late winter-early spring, with serious implication for water availability during summer, when precipitation is a minimum over the mountains. We also explore changes in the albedo, as a contributing factor affecting the net flux of energy at the surface and found a reduction in albedo of 20–60% at high elevations, related to the elevation dependent warming. Furthermore, a decrease in winter precipitation is projected in central Chile by the end of the century, independent of the scenario considered.Fil: Zazulie, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Rusticucci, Matilde Monica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Raga, Graciela B.. Universidad Nacional Autónoma de México; Méxic

Spatio-temporal mapping of glacier fluctuations in the subtropical Central Andes: Case studies of Alto Del Plomo and Volcan Maipo

Glaciers located in the Subtropical Central Andes region, play an important role in the surrounding hydrological system due to their significant contribution to the runoff of Andean rivers. Furthermore, they constitute a natural water reservoir that can buffer the impact of meteorological droughts seasons on socioeconomic activities in the region. The Intergovernmental Panel on Climate Change (IPCC (2013)) has concluded that glaciers have clearly shrunk at global scale. Nevertheless there is a need to quantify variations at a local-to-regional scale. In this interdisciplinary work we make use of the Geographic Information System tool in a climatic study with the purpose of visualizing spatial and temporal changes in glaciers’ extension through a multi-temporal analysis of satellite images in the period 1989–2015. Two glaciers in the Subtropical Central Andes region were selected: Alto del Plomo glacier (32.98°S–70.01°W) in the Plomo river basin and Volcán Maipo glacier (34.16°S–69.8°W). The accumulation zones for both glaciers are found at similar altitudes and distant only by less than 130 km, but they have different morphological characteristics and the Volcán Maipo glacier is located within a protected area in the natural reserve of Laguna del Diamante. The results of the analysis indicate a decrease in the total area (18%) of Alto del Plomo glacier that is especially evident in its glacier tongue. In contrast, the Volcán Maipo glacier presented almost no change in the 27-year period considered. The climate factors, temperature and nival precipitation, that affect the evolution of the areal extent of the glaciers do not seem to fully explain the different behavior seen in these two glaciers. It is suggested here that the environmental factors that surround them might explain the observed behavior.Fil: Zazulie, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Briche, Elodie Sylvie Odile. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Raga, Graciela B.. Universidad Nacional Autónoma de México; MéxicoFil: Rusticucci, Matilde Monica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Modulation of boreal extended summer tropical cyclogenesis over the northwest Pacific by the quasi-biweekly oscillation under different El Nino-southern oscillation phases

The study of the interannual and intraseasonal modulation of tropical cyclogenesis (TCG) in the northwest Pacific (NWP) basin has received significant attention in the past. Most previous studies have focused on the individual impact of El Nino-southern oscillation (ENSO) or Madden-Julian Oscillation on TCG, whereas the combined effect of ENSO and another leading intraseasonal oscillation mode, quasi-biweekly oscillation (QBWO), on NWP TCG has rarely been studied. Therefore, this study systemically investigates the modulation of NWP TCG by the QBWO under different ENSO phases. A significant modulation of TCG by QBWO in the ENSO neutral years is observed, with significantly increased (decreased) TCG over the NWP in QBWO active (inactive) phases. Moreover, during El Nino years and La Nina years, the modulation of TCG by QBWO is not significant and no distinctive difference in the TCG frequency can be detected. Further analyses show that the modulation of TCG by the QBWO is mainly related to the changes in large-scale environment and energy that affect TCG associated with active or inactive phases of the QBWO under different ENSO phases. Large-scale environmental factors and energy are more favourable for TCG during ENSO neutral years compared with El Nino and La Nina years. These results are associated with QBWO cycle under the impact of background (e.g., boundary layer moisture and zonal wind shear) which is determined by ENSO conditions

Properties of small cirrus ice crystals from commercial aircraft measurements and implications for flight operations

Measurements of cloud ice crystal size distributions have been made by a backscatter cloud probe (BCP) mounted on five commercial airliners flying international routes that cross five continents. Bulk cloud parameters were also derived from the size distributions. As of 31 December 2014, a total of 4399 flights had accumulated data from 665 hours in more than 19 000 cirrus clouds larger than 5 km in length. The BCP measures the equivalent optical diameter (EOD) of individual crystals in the 5–90 µm range from which size distributions are derived and recorded every 4 seconds. The cirrus cloud property database, an ongoing development stemming from these measurements, registers the total crystal number and mass concentration, effective and median volume diameters and extinction coefficients derived from the size distribution. This information is accompanied by the environmental temperature, pressure, aircraft position, date and time of each sample. The seasonal variations of the cirrus cloud properties measured from 2012 to 2014 are determined for six geographic regions in the tropics and extratropics. Number concentrations range from a few per litre for thin cirrus to several hundreds of thousands for heavy cirrus. Temperatures range from 205 to 250 K and effective radii from 12 to 20 µm. A comparison of the regional and seasonal number and mass size distributions, and the bulk microphysical properties derived from them, demonstrates that cirrus properties cannot be easily parameterised by temperature or by latitude. The seasonal changes in the size distributions from the extratropical Atlantic and Eurasian air routes are distinctly different, showing shifts from mono-modal to bi-modal spectra out of phase with one another. This phase difference may be linked to the timing of deep convection and cold fronts that lead to the cirrus formation. Likewise, the size spectra of cirrus over the tropical Atlantic and Eastern Brazil differ from each other although they were measured in adjoining regions. The cirrus crystals in the maritime continental tropical region over Malaysia form tri-modal spectra that are not found in any of the other regions measured by the IAGOS aircraft so far, a feature that is possibly linked to biomass burning or dust. Frequent measurements of ice crystal concentrations greater than 1×105 L−1, often accompanied by anomalously warm temperature and erratic airspeed readings, suggest that aircraft often experience conditions that affect their sensors. This new instrument, if used operationally, has the potential of providing real-time and valuable information to assist in flight operations as well as providing real-time information for along-track nowcasting

Science-policy dialogues for water security : addressing vulnerability and adaptation to global change in the arid Americas

Given the multidimensional nature of vulnerability, where climate interacts with many other stressors, adaptation ought to feature in national and regional development priorities. Based on ongoing experience, the following conditions can be considered as essential for successful science-policy dialogues: inclusivity, involvement, interaction, and influence. Allocating available water resources, monitoring environmental impacts, and abating pollution have historically been the purview of government agencies. The problem more often than not is lack of capacity (funds, staff, or knowledge). But with rising decentralization, businesses and communities are expected to assume a growing responsibility to ensure water security