Search results for "Anticyclone"

Water vapor increase in the northern lower stratosphere by the Asian monsoon anticyclone observed during TACTS/ESMVal campaigns

2017

Abstract. The impact of air masses from Asia influenced by the Asian monsoon anticyclone on the northern hemispheric stratosphere is investigated based on in-situ measurements. An statistical significant increase in water vapor of about 0.5 ppmv (11 %) and methane up to 20 ppbv (1.2 %) in the extra-tropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 by in-situ instrumentation in the northern hemisphere during the HALO aircraft mission TACTS and ESMVal. We investigate the origin of this water vapor and methane increase with the help of the three-dimensional Lagrangian chemistry transport model CLaMS. We assign the source of the moist ai…

Modelling circulation in an ice-covered lake

2010

In deep ice-covered lakes with temperatures below 4 °C the heat flux from the bottom sediment results in a horizontal density gradient and a consequent flow along the bottom slope. Measurements in Lake Paajarvi, Finland, show a stable temperature field where a heat gain through the bottom and a heat loss through the ice nearly balance each other. The circulation is thermal with low velocities (less than 1.5 cm s -1 ). We used the 3D hydrodynamic Princeton Ocean Model as a tool to simulate the water circulation and the temperature distribution under the ice. The model forcing was based on field temperature measurements. The model simulations suggest that in midwinter the velocity field of th…

Impact of the Asian monsoon on the extratropical lower stratosphere: trace gas observations during TACTS over Europe 2012

2016

Abstract. The transport of air masses originating from the Asian monsoon anticyclone into the extratropical upper troposphere and lower stratosphere (Ex-UTLS) above potential temperatures Θ =  380 K was identified during the HALO aircraft mission TACTS in August and September 2012. In situ measurements of CO, O3 and N2O during TACTS flight 2 on 30 August 2012 show the irreversible mixing of aged stratospheric air masses with younger (recently transported from the troposphere) ones within the Ex-UTLS. Backward trajectories calculated with the trajectory module of CLaMS indicate that these tropospherically affected air masses originate from the Asian monsoon anticyclone. These air masses are …

Recent changes in air temperature, heat waves occurrences, and atmospheric circulation in Northern Africa

2013

This study documents the time evolution of air temperature and heat waves occurrences over Northern Africa for the period 1979-2011. A significant warming (1°-3°C), appearing by the mid-1960s over Sahara and Sahel, is associated with higher/lesser frequency of warm/cold temperatures, as with longer duration and higher occurrences of heat waves. Heat waves episodes of at least 4 day duration have been examined after removing the long-term evolution. These episodes are associated with specific anomalies: (i) in spring, positive low-level temperature anomalies over the Sahel and Sahara; low and midlevel cyclonic rotation over Morocco associated with a Rossby wave pattern, lessening the Harmatt…

A case study of the radiative effect of aerosols over Europe: EUCAARI-LONGREX

2016

Abstract. The radiative effect of anthropogenic aerosols over Europe during the 2008 European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions Long Range Experiment (EUCAARI-LONGREX) campaign has been calculated using measurements collected by the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 aircraft and radiative transfer modelling. The aircraft sampled anthropogenically perturbed air masses across north-western Europe under anticyclonic conditions with aerosol optical depths ranging from 0.047 to 0.357. For one specially designed “radiative closure” flight, simulated irradiances have been compared to radiation measurements for a case of aged Europe…

Global Climatologies of Eulerian and Lagrangian Flow Features based on ERA-Interim

2017

Abstract This paper introduces a newly compiled set of feature-based climatologies identified from ERA-Interim (1979–2014). Two categories of flow features are considered: (i) Eulerian climatologies of jet streams, tropopause folds, surface fronts, cyclones and anticyclones, blocks, and potential vorticity streamers and cutoffs and (ii) Lagrangian climatologies, based on a large ensemble of air parcel trajectories, of stratosphere–troposphere exchange, warm conveyor belts, and tropical moisture exports. Monthly means of these feature climatologies are openly available at the ETH Zürich web page (http://eraiclim.ethz.ch) and are annually updated. Datasets at higher resolution can be obtained…

2020

Abstract. This study presents airborne in situ and satellite remote sensing climatologies of cirrus clouds and humidity. The climatologies serve as a guide to the properties of cirrus clouds, with the new in situ database providing detailed insights into boreal midlatitudes and the tropics, while the satellite-borne data set offers a global overview. To this end, an extensive, quality-checked data archive, the Cirrus Guide II in situ database, is created from airborne in situ measurements during 150 flights in 24 campaigns. The archive contains meteorological parameters, ice water content (IWC), ice crystal number concentration (Nice), ice crystal mean mass radius (Rice), relative humidity …

2018

Abstract. The impact of air masses originating in Asia and influenced by the Asian monsoon anticyclone on the Northern Hemisphere stratosphere is investigated based on in situ measurements. A statistically significant increase in water vapor (H2O) of about 0.5 ppmv (11 %) and methane (CH4) of up to 20 ppbv (1.2 %) in the extratropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 during the HALO aircraft missions Transport and Composition in the UT/LMS (TACTS) and Earth System Model Validation (ESMVal). We investigate the origin of the increased water vapor and methane using the three-dimensional Chemical Lagrangian Model of the Stratosph…

2016

Abstract. Global simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) using artificial tracers of air mass origin are used to analyze transport mechanisms from the Asian monsoon region into the lower stratosphere. In a case study, the transport of air masses from the Asian monsoon anticyclone originating in India/China by an eastward-migrating anticyclone which broke off from the main anticyclone on 20 September 2012 and filaments separated at the northeastern flank of the anticyclone are analyzed. Enhanced contributions of young air masses (younger than 5 months) are found within the separated anticyclone confined at the top by the thermal tropopause. Further, these a…

In situ observation of new particle formation (NPF) in the tropical tropopause layer of the 2017 Asian monsoon anticyclone – Part 1: Summary of Strat…

2021

During the monsoon season of the year 2017 the airborne StratoClim mission took place in Kathmandu, Nepal, with eight mission flights of the M-55 Geophysica in the upper troposphere–lower stratosphere (UTLS) of the Asian monsoon anticyclone (AMA) over northern India, Nepal, and Bangladesh. More than 100 events of new particle formation (NPF) were observed. In total, more than 2 h of flight time was spent under NPF conditions as indicated by the abundant presence of nucleation-mode aerosols, i.e. with particle diameters dp smaller than 15 nm, which were detected in situ by means of condensation nuclei counting techniques. Mixing ratios of nucleation-mode particles (nnm) of up to ∼ 50 000 mg−…