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Search Results: 1 - 10 of 200606 matches for " P. Hartogh "
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First detection of tidal behaviour in polar mesospheric water vapour by ground based microwave spectroscopy
K. Hallgren ,P. Hartogh
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: Mesospheric water vapour has been observed above ALOMAR in northern Norway (69° N 16° E) by our group since 1995 using a 22 GHz ground based microwave spectrometer. A new instrument with higher sensitivity, providing a much better time resolution especially in the upper mesosphere, was installed in May 2008. The time resolution is high enough to provide observations of daily variations in the water vapour mixing ratio. We present the first ground based detections of tidal behaviour in the polar middle atmospheric water vapour distribution. Diurnal and semidiurnal variations of water vapour have been observed and due to the long chemical lifetime of water they are assumed to be caused by changing wind patterns which transport water-rich or poor air into the observed region. The detected tidal behaviour does not follow any single other dynamical field but is instead assumed to be a result of the different wind components. Both the diurnal and semidiurnal amplitude and phase components are resolved. The former shows a stable seasonal behaviour consistent with earlier observations of wind fields and model calculations, whereas the latter appears more complex and no regular behaviour has so far been observed.
Upper stratospheric ozone decrease events due to a positive feedback between ozone and the ozone dissociation rate
G. R. Sonnemann,P. Hartogh
Nonlinear Processes in Geophysics (NPG) , 2009,
Abstract: Ozone measurements taken with a ground based microwave instrument at Lindau (51.66° N, 10.13° E) over some years showed strong ozone decrease events within the stratopause region, particularly during the winter half-year. These events are characterized by a marked drop of the ozone mixing ratio from two to three ppmv to less than half a ppmv in extreme cases. Simultaneous water vapor measurements at the same place, also carried out by a microwave instrument, showed a strong increase of its mixing ratio and the temperature was also enhanced during these episodes. The theoretical analysis brought evidence that these events result from a positive feedback in the complex radiatively-chemical system between the ozone column density and the ozone dissociation rate.
Long-term trends of the concentration of the minor constituents in the mesosphere – a model study
M. Grygalashvyly,G. R. Sonnemann,P. Hartogh
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: We investigate the influence of the rising concentrations of methane, dinitrogen oxide and carbon dioxide since the pre-industrial era upon the chemistry of the mesosphere. We use for calculations our global 3D-model COMMA-IAP designed for the exploration of the MLT-region and particularly the extended mesopause region. In order to get approximated data of the solar Lyman-α flux back to the pre-industrial time, we derived a quadratic fit using the sunspot number available since 1749 as the only solar proxy for the Lyman-α flux before 1947. The Lyman-α flux values are employed to determine the water vapor dissociation rate. The water vapor trend analysis utilizes estimated methane trends since the pre-industrial era. An unsolved problem for the model calculations consists of the water vapor mixing ratio at the hygropause during the time range of trend calculation. We assume that the hygropause was dryer at the pre-industrial time than currently. As a consequence of the methane oxidation, the middle atmosphere became more humid according to the rising methane concentration, but depending on height and with a small time delay of few years. The solar influence on the water vapor mixing ratio is insignificant below about 80 km within summery high latitudes, but it becomes increasingly more important above this altitude. The growing water vapor concentration increases the hydrogen radical concentration and reduces the mesospheric ozone. A second region of stronger ozone decrease is located in the vicinity of the stratopause. Increasing CO2 concentration enhances slightly the concentration of CO in the mesosphere, but its influence upon the chemistry is small and its main effect is connected with a cooling of the upper atmosphere. We discuss the trends particularly in view of the impact on the NLC region.
Climatology of middle atmospheric water vapour above the ALOMAR observatory in northern Norway
K. Hallgren,P. Hartogh,C. Jarchow
Atmospheric Chemistry and Physics Discussions , 2012, DOI: 10.5194/acpd-12-31531-2012
Abstract: We have been observing the water vapour line at 22.235 GHz above ALOMAR in northern Norway (69° N, 16° E) since early 1996 with ground-based microwave spectrometers (WASPAM and cWASPAM) and will here describe a climatology based on these observations. Maintenance, different spectrometers and upgrades of the hardware have slightly changed the instruments. Therefore great care has been taken to make sure the different datasets are compatible with each other. In order to maximise the sensitivity at high altitude for the older instrument a long integration time (168 h) was chosen. The complete dataset was thereafter recompiled into a climatology which describes the yearly variation of water vapour at polar latitudes on a weekly basis. The atmosphere is divided into 16 layers between 40–80 km, each 2.5 km thick. The dataset, spanning 15 yr from 1996 to 2010, enabled us to investigate the long-term behaviour of water vapour at these latitudes. By comparing the measurements from every year to the climatological mean we were also able to look for indications of trends in the dataset at different altitudes during the time period of our observations. In general there is a weak negative trend which differs slightly at different altitudes. There are however no drifts in the annual variation of water vapour from the point of view of onset of summer and winter. We compare our climatology to the reference water vapour profiles from AFGL, a free and easy accessible reference atmosphere. There are strong deviations between our observations and the reference profile, therefore we publish our climatological dataset in a table in the paper.
Long-term behavior of the concentration of the minor constituents in the mesosphere – a model study
M. Grygalashvyly,G. R. Sonnemann,P. Hartogh
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: We investigate the influence the rising concentrations of methane, nitrous oxide and carbon dioxide which have occurred since the pre-industrial era, have had on the chemistry of the mesosphere. For this investigation we use our global 3-D-model COMMA-IAP which was designed for the exploration of the MLT-region and in particular the extended mesopause region. Assumptions and approximations for the trends in the Lyman-α flux (needed for the water vapor dissociation rate), methane and the water vapor mixing ratio at the hygropause are necessary to accomplish this study. To approximate the solar Lyman-α flux back to the pre-industrial time, we derived a quadratic fit using the sunspot number record which extends back to 1749 and is the only solar proxy available for the Lyman-α flux prior to 1947. We assume that methane increases with a constant growth rate from the pre-industrial era to the present. An unsolved problem for the model calculations consists of how the water vapor mixing ratio at the hygropause should be specified during this period. We assume that the hygropause was dryer during pre-industrial times than the present. As a consequence of methane oxidation, the model simulation indicates that the middle atmosphere has become more humid as a result of the rising methane concentration, but with some dependence on height and with a small time delay of few years. The solar influence on the water vapor mixing ratio is insignificant below about 80 km in summer high latitudes, but becomes increasingly more important above this altitude. The enhanced water vapor concentration increases the hydrogen radical concentration and reduces the mesospheric ozone. A second region of stronger ozone decrease is located in the vicinity of the stratopause. Increases in CO2 concentration enhance slightly the concentration of CO in the mesosphere. However, its influence upon the chemistry is small and its main effect is connected with a cooling of the upper atmosphere. The long-term behavior of water vapor is discussed in particular with respect to its impact on the NLC region.
New sub-millimeter heterodyne observations of CO and HCN in Titan's atmosphere with the APEX Swedish Heterodyne Facility Instrument
M. Rengel,H. Sagawa,P. Hartogh
Physics , 2010,
Abstract: The origin of the atmosphere of the largest moon of Saturn, Titan, is poorly understood and its chemistry is rather complicated. Ground-based millimeter/sub-millimeter heterodyne spectroscopy resolves line shapes sufficiently to determine information in Titan's atmospheric composition (on vertical profiles and isotopic ratios). We test the capabilities of the Swedish Heterodyne Facility Instrument (SHFI), Receiver APEX-1, together with the Atacama Pathfinder EXperiment APEX 12-m telescope for Titan's atmospheric observations. In particular we present sub-millimeter observations of the CO(2-1) and HCN(3-2) lines of the Titan stratosphere with APEX, and with SHFI taken during the Science Verification (SV) instrument phase on March and June 2008. With the help of appropriate radiative transfer calculations we investigate the possibility to constrain the chemical concentrations and optimize the performance of the APEX-1 instrument for inferring vertical profiles of molecular components of the atmosphere of Titan.
Noctilucent clouds and the mesospheric water vapour: the past decade
U. von Zahn,U. Berger,J. Fiedler,P. Hartogh
Atmospheric Chemistry and Physics Discussions , 2004,
Abstract: The topic of this paper is the expected (from modelling) and observed sensitivity of the brightness β of noctilucent clouds (NLC) on the ambient water vapour mixing ratio f(H2O). Firstly, we show that state-of-the-art models of NLC layer formation predict that in the Arctic summer, a 10% increase of f(H2O) in the upper mesosphere should lead to a 22% increase in β. Secondly, we review observations of episodic changes in f(H2O) and those in β, the former being available since 1992, the latter since 1979. We also add a new series of observations of f(H2O) in the Arctic summer, performed at the ALOMAR observatory (69° N). Thirdly, we show that an increase in daily averaged f(H2O) observed in the Arctic summer since 1996, when introduced into the NLC models, comes close to explaining the observed increase in β. In contrast to this gratifying situation for the summer means of f(H2O) and β (the latter being available only in summer anyway), the behaviour of annual means of f(H2O) is quite different. Those indicate that since 1996 significant decreases of annually averaged upper mesospheric water vapour have occurred at low, mid, and high latitude which can not be used to explain the observed near-stability in NLC brightness over this time period. We close with comments on the very different character of decadal variations in NLC brightness and occurrence rate.
A QBO-signal in mesospheric water vapor measurements at ALOMAR (69.29° N, 16.03° E) and in model calculations by LIMA over a solar cycle
G. R. Sonnemann,P. Hartogh,S. Li,M. Grygalashvyly
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: Microwave water vapor measurements between 40 and 80 km over a solar cycle (1996–2006) were carried out in high latitudes at ALOMAR (69.29° N, 16.03° E), Norway. Three larger interuptions in the winters of 1996/97 and 2005/06, and from spring 2001 to spring 2002, a few smaller interruptions of monitoring occurred during this period. The observed year-to-year variability is not directly related to the solar activity. The analysis of the observations by the Fast Fourier Transform (FFT) method revealed peaks close to two years, particularly in the upper monitoring domain. Model calculations by means of the real date model LIMA, Leibniz-Institute Middle Atmosphere model, reflect essential patterns of the water vapor variation. The FFT-analysis of the calculated water vapor mixing ratios also showed peaks of around two years. The real period of the QBO during the monitoring period ranged quite close to two years within the time interval considered, with the exception of the years 2001/02 when the period was essentially longer. Although the QBO is a phenomenon occurring in the zonal wind of the tropical stratosphere, we suppose an influence of the QBO on the water vapor distribution of the mesosphere of high latitudes controlled by transport processes. A possible link could be given by the planetary wave activity triggered by the QBO.
GREAT: the SOFIA high-frequency heterodyne instrument
S. Heyminck,U. U. Graf,R. Güsten,J. Stutzki,H. W. Hübers,P. Hartogh
Physics , 2012, DOI: 10.1051/0004-6361/201218811
Abstract: We describe the design and construction of GREAT, the German REceiver for Astronomy at Terahertz frequencies operated on the Stratospheric Observatory for Infrared Astronomy (SOFIA). GREAT is a modular dual-color heterodyne instrument for highresolution far-infrared (FIR) spectroscopy. Selected for SOFIA's Early Science demonstration, the instrument has successfully performed three Short and more than a dozen Basic Science flights since first light was recorded on its April 1, 2011 commissioning flight. We report on the in-flight performance and operation of the receiver that - in various flight configurations, with three different detector channels - observed in several science-defined frequency windows between 1.25 and 2.5 THz. The receiver optics was verified to be diffraction-limited as designed, with nominal efficiencies; receiver sensitivities are state-of-the-art, with excellent system stability. The modular design allows for the continuous integration of latest technologies; we briefly discuss additional channels under development and ongoing improvements for Cycle 1 observations. GREAT is a principal investigator instrument, developed by a consortium of four German research institutes, available to the SOFIA users on a collaborative basis.
Preparation for the Solar system observations with Herschel: Simulation of Jupiter observations with PACS
H. Sagawa,P. Hartogh,M. Rengel,A. de Lange,T. Cavalie
Physics , 2010, DOI: 10.1016/j.pss.2010.05.011
Abstract: Observations of the water inventory as well as other chemically important species on Jupiter will be performed in the frame of the guaranteed time key project of the Herschel Space Observatory entitled "Water and related chemistry in the Solar system". Among other onboard instruments, PACS (Photodetector Array Camera and Spectrometer) will provide new data of the spectral atlas in a wide region covering the far-infrared and submillimetre domains, with an improved spectral resolution and a higher sensitivity compared to previous observations carried out by Cassini/CIRS (Composite InfraRed Spectrometer) and by ISO (Infrared Space Observatory). In order to optimise the observational plan and to prepare for the data analysis, we have simulated the expected spectra of PACS Jupiter observations. Our simulation shows that PACS will promisingly detect several H2O emission lines. As PACS is capable of spatially resolving the Jovian disk, we will be able to discern the external oxygen sources in the giant planets by exploring the horizontal distribution of water. In addition to H2O lines, some absorption lines due to tropospheric CH4, HD, PH3 and NH3 lines will be observed with PACS. Furthermore, owing to the high sensitivity of the instrument, the current upper limit on the abundance of hydrogen halides such as HCl will be also improved.
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