Search results for "GW"

Air traffic and contrail changes during COVID-19 over Europe: A model study

2021

The strong reduction of air traffic during the COVID-19 pandemic provides a test case for the relation between air traffic density, contrails, and their radiative forcing of climate change. Air traffic and contrail cirrus changes are quantified for a European domain for March to August 2020 and compared to the same period in 2019. Traffic data show a 72 % reduction in flight distance compared with 2019. This paper investigates the induced contrail changes in a model study. The contrail model results depend on various methodological details tested in parameter studies. In the reference case, the reduced traffic caused an even stronger reduction in contrail length, partly because the w…

Comparison of top of the atmosphere GERB measured radiances with independent radiative transfer simulations obtained at the Valencia Anchor Station a…

2005

The purpose of this work is to compare top of the atmosphere (TOA) radiances as measured by the Geostationary Earth Radiation Budget (GERB) instrument on board the METEOSAT-8 (METEOSAT Second Generation) satellite to equivalent independent radiances obtained from radiative transfer simulations performed using surface and atmospheric measured parameters gathered during the GERB Surface Ground Validation Campaign at the Valencia Anchor Station (VAS) reference area in February 2004. In this paper we try to extend the methodology previously developed and tested for the NASA Clouds and the Earth's Radiant Energy System (CERES) instrument in the framework of the SEVIRI and GERB Cal/val Area for L…

Cold cloud microphysical process rates in a global chemistry–climate model

2021

Microphysical processes in cold clouds which act as sources or sinks of hydrometeors below 0 ∘C control the ice crystal number concentrations (ICNCs) and in turn the cloud radiative effects. Estimating the relative importance of the cold cloud microphysical process rates is of fundamental importance to underpin the development of cloud parameterizations for weather, atmospheric chemistry, and climate models and to compare the output with observations at different temporal resolutions. This study quantifies and investigates the ICNC rates of cold cloud microphysical processes by means of the chemistry–climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) and defines the hierarchy of sources…

2021

Abstract. The strong reduction of air traffic during the COVID-19 pandemic provides a unique test case for the relationship between air traffic density, contrails, and their radiative forcing of climate change. Here, air traffic and contrail cirrus changes are quantified for a European domain for March to August 2020 and compared to the same period in 2019. Traffic data show a 72 % reduction in flight distance compared with 2019. This paper investigates the induced contrail changes in a model study. The contrail model results depend on various methodological details as discussed in parameter studies. In the reference case, the reduced traffic caused a reduction in contrail length. The reduc…

Heating rate profiles and radiative forcing due to a dust storm in the Western Mediterranean using satellite observations

2017

Abstract We analyze the vertically-resolved radiative impact due to a dust storm in the Western Mediterranean. The dust plume travels around 3–5 km altitude and the aerosol optical depth derived by MODIS at 550 nm ranges from 0.33 to 0.52 at the overpass time (13:05 UT). The aerosol radiative forcing (ARF), forcing efficiency (FE) and heating rate profile (AHR) are determined throughout the dust trajectory in shortwave (SW) and longwave (LW) ranges. To do this, we integrate different satellite observations (CALIPSO and MODIS) and detailed radiative transfer modeling. The combined (SW + LW) effect of the dust event induces a net cooling in the studied region. On average, the FE at 22.4° sola…

Aviation Contrail Cirrus and Radiative Forcing Over Europe During 6 Months of COVID‐19

2021

Abstract The COVID‐19 pandemic led to a 72% reduction of air traffic over Europe in March–August 2020 compared to 2019. Modeled contrail cover declined similarly, and computed mean instantaneous radiative contrail forcing dropped regionally by up to 0.7 W m−2. Here, model predictions of cirrus optical thickness and the top‐of‐atmosphere outgoing longwave and reflected shortwave irradiances are tested by comparison to Meteosat‐SEVIRI‐derived data. The agreement between observations and modeled data is slightly better when modeled contrail cirrus contributions are included. The spatial distributions and diurnal cycles of the differences in these data between 2019 and 2020 are partially caused…

Observed versus simulated mountain waves over Scandinavia – improvement of vertical winds, energy and momentum fluxes by enhanced model resolut…

2017

Abstract. Two mountain wave events, which occurred over northern Scandinavia in December 2013 are analysed by means of airborne observations and global and mesoscale numerical simulations with horizontal mesh sizes of 16, 7.2, 2.4 and 0.8 km. During both events westerly cross-mountain flow induced upward-propagating mountain waves with different wave characteristics due to differing atmospheric background conditions. While wave breaking occurred at altitudes between 25 and 30 km during the first event due to weak stratospheric winds, waves propagated to altitudes above 30 km and interfacial waves formed in the troposphere at a stratospheric intrusion layer during the second event. Global an…

Aerosol influence on radiative cooling

2011

Aerosol particles have a complex index of refraction and therefore contribute to atmospheric emission and radiative cooling rates. In this paper calculations of the longwave flux divergence within the atmosphere at different heights are presented including water vapour and aerosol particles as emitters and absorbers. The spectral region covered is 5 to 100 microns divided into 23 spectral intervals. The relevant properties of the aerosol particles, the single scattering albedo and the extinction coefficient, were first calculated by Mie-theory and later by an approximation formula with a complex index of refraction given by Volz. The particle growth with relative humidity is also incorporat…

Investigation of the mixing layer height derived from ceilometer measurements in the Kathmandu Valley and implications for local air quality

2017

Abstract. In this study 1 year of ceilometer measurements taken in the Kathmandu Valley, Nepal, in the framework of the SusKat project (A Sustainable Atmosphere for the Kathmandu Valley) were analysed to investigate the diurnal variation of the mixing layer height (MLH) and its dependency on the meteorological conditions. In addition, the impact of the MLH on the temporal variation and the magnitude of the measured black carbon concentrations are analysed for each season. Based on the assumption that black carbon aerosols are vertically well mixed within the mixing layer and the finding that the mixing layer varies only little during night time and morning hours, black carbon emission fluxe…

Recent changes in precipitation, ITCZ convection and northern tropical circulation over North Africa (1979-2007)

2011

This article focuses on some recent changes observed in the Tropics with special emphasis on the African monsoon region using high-resolution gridded precipitation from the Climatic Research Unit (period 1979–2002), outgoing longwave radiation at the top of the atmosphere from the National Oceanic and Atmospheric Administration and atmospheric reanalyses from the Climate Prediction Center (NCEP-DOE2, period 1979–2007). The results show a rainfall increase in North Africa since the mid-90s with significant northward migrations of rainfall amounts, i.e. + 1.5° for the 400 mm July to September isohyets, whereas deep convection has significantly increased and shifted northward. The subsidence b…