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A statistical approach to quantify uncertainty in carbon monoxide measurements at the Iza a global GAW station: 2008–2011  [PDF]
A. J. Gomez-Pelaez,R. Ramos,V. Gomez-Trueba,P. C. Novelli
Atmospheric Measurement Techniques Discussions , 2012, DOI: 10.5194/amtd-5-6949-2012
Abstract: Atmospheric CO in-situ measurements are carried out at the Iza a (Tenerife) global GAW mountain station using a RGA (Reduction Gas Analyser). In-situ measurements at Iza a are representative of the subtropical North-East Atlantic free troposphere, specially during the night period. We present the measurement system configuration, the response function, the calibration scheme, the data processing, the Iza a's 2008–2011 CO nocturnal time series, and the mean diurnal cycle by months. We have developed a rigorous uncertainty analysis for carbon monoxide measurements carried out at the Iza a station which could be applied to other GAW stations. We determine the combined standard uncertainty from four components of the measurement: uncertainty of the WMO standard gases interpolated over the range of measurement, the uncertainty that takes into account the agreement between the standard gases and the response function used, the uncertainty due to the repeatability of the injections, and the propagated uncertainty related to the response function parameters uncertainties (which also takes into account the covariance between the parameters). The mean value of the combined standard uncertainty decreased significantly after March 2009, from 2.37 nmol mol 1 to 1.66 nmol mol 1, due to improvements in the measurement system. A fifth type of uncertainty we call representation uncertainty is considered when some of the data necessary to compute exactly the mean are absent. Any computed mean has also a propagated uncertainty arising from the uncertainties of the data used to compute the mean. The law of propagation depends on the type of uncertainty component (random or systematic). In-situ hourly means are compared with simultaneous and collocated NOAA flask samples. The uncertainty in the differences is determined and whether these are significant. For 2009–2011, only 24.5% of the differences are significant, and 68% of the differences are between 2.39 and 2.5 nmol mol 1. Total and annual mean differences are computed using conventional expressions but also expressions with weights based on the minimum variance method. The annual mean differences for 2009–2011 are well within the ±2 nmol mol 1 compatibility goal of GAW.
Orographic cirrus in the future climate  [PDF]
H. Joos,P. Spichtinger,U. Lohmann
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: A cloud resolving model (CRM) is used to investigate the formation of orographic cirrus clouds in the current and future climate. The formation of cirrus clouds depends on a variety of dynamical and thermodynamical processes, which act on different scales. First, the capability of the CRM in realistically simulating orographic cirrus clouds has been tested by comparing the simulated results to aircraft measurements of an orographic cirrus cloud. The influence of a warmer climate on the microphysical and optical properties of cirrus clouds has been investigated by initializing the CRM with vertical profiles of horizontal wind, temperature and moisture from IPCC A1B simulations for the current climate and for the period 2090–2099 for two regions representative for North and South America. In a future climate, the increase in moisture dampens the vertical propagation of gravity waves and the occurring vertical velocities. Together with higher temperatures fewer ice crystals nucleate homogeneously. Assuming that the relative humidity does not change in a warmer climate the specific humidity in the model is increased. This increase in specific humidity in a warmer climate results in a higher ice water content. The net effect of a reduced ice crystal number concentration and a higher ice water content is an increased optical depth.
Interaction of Orographic Disturbance with Front
Wang Xingbao,Wu Rongsheng,
Wang Xingbao
,Wu Rongsheng

大气科学进展 , 1999,
Abstract: The interaction of orographic disturbance with front is investigated with a nonhydrostatic fully compressible mesoscale model (ARPS). It is shown that the front is dominated mainly by the orographic dis-turbance if the front is weak. Firstly, because the stratified airstream is forced lo flow along the topographic surface, the topographic surface almost coincides with the lowest isentrope for the barotropic flow. The po-tential temperature gradients are opposite on upwind slope and downwind slope. As the cold front moves across the mountain, its intensity decreases on the upwind side and increases on the downwind side due to the thermal superposition. Conversely, the warm front is strengthened on the upwind slope and weakened on the downwind slope. This is the thermal superposition effect. Secondly, the mountain-forced circulation and orographic waves, which depend on the shape and size of topography and characteristics of airflow, contribute to frontogenesis and /or frontolysis. This is referred as dynamical action. For the mesoscale mountain ridge of gentle slope, the dynamical action weakens the cold front on the upwind slope, and strengthens the cold front on the lee side. While for the mesoscale mountain of steep slope, the dynamical ef-fect weakens the cold front on the upwind side and strengthens the cold front on the mountain top, the frontal intensity is decreased when front moves downslope rapidly. As front moves into the convergent zone near the mountain base, its intensity is enhanced severely. If the front is intensive, there is strong interaction between the orographic disturbance and the front. The cold front dramatically increases downslope wind and lee side gravity wave activity. And these in turn act upon the frontal intensity and frontal structure. For the baroclinic basic flow, the southerly warm advection on the upwind side makes the cold front less frontolysis; the northerly on the lee side violently intensifies the clod front.
A statistical approach to quantify uncertainty in carbon monoxide measurements at the Iza a global GAW station: 2008–2011
A. J. Gomez-Pelaez, R. Ramos, V. Gomez-Trueba, P. C. Novelli,R. Campo-Hernandez
Atmospheric Measurement Techniques (AMT) & Discussions (AMTD) , 2013,
Abstract: Atmospheric CO in situ measurements are carried out at the Iza a (Tenerife) global GAW (Global Atmosphere Watch Programme of the World Meteorological Organization – WMO) mountain station using a Reduction Gas Analyser (RGA). In situ measurements at Iza a are representative of the subtropical Northeast Atlantic free troposphere, especially during nighttime. We present the measurement system configuration, the response function, the calibration scheme, the data processing, the Iza a 2008–2011 CO nocturnal time series, and the mean diurnal cycle by months. We have developed a rigorous uncertainty analysis for carbon monoxide measurements carried out at the Iza a station, which could be applied to other GAW stations. We determine the combined standard measurement uncertainty taking into consideration four contributing components: uncertainty of the WMO standard gases interpolated over the range of measurement, the uncertainty that takes into account the agreement between the standard gases and the response function used, the uncertainty due to the repeatability of the injections, and the propagated uncertainty related to the temporal consistency of the response function parameters (which also takes into account the covariance between the parameters). The mean value of the combined standard uncertainty decreased significantly after March 2009, from 2.37 nmol mol 1 to 1.66 nmol mol 1, due to improvements in the measurement system. A fifth type of uncertainty we call representation uncertainty is considered when some of the data necessary to compute the temporal mean are absent. Any computed mean has also a propagated uncertainty arising from the uncertainties of the data used to compute the mean. The law of propagation depends on the type of uncertainty component (random or systematic). In situ hourly means are compared with simultaneous and collocated NOAA flask samples. The uncertainty of the differences is computed and used to determine whether the differences are significant. For 2009–2011, only 24.5% of the differences are significant, and 68% of the differences are between 2.39 and 2.5 nmol mol 1. Total and annual mean differences are computed using conventional expressions but also expressions with weights based on the minimum variance method. The annual mean differences for 2009–2011 are well within the ±2 nmol mol 1 compatibility goal of GAW.
Quality assessment of Iza a's upper-air water vapour measurement techniques: FTIR, Cimel, MFRSR, GPS, and Vaisala RS92  [PDF]
M. Schneider,P. M. Romero,F. Hase,T. Blumenstock
Atmospheric Measurement Techniques Discussions , 2009,
Abstract: At the Iza a Atmospheric Research Centre water vapour amounts are measured routinely by different techniques since many years. We intercompare the total precipitable water vapour amounts measured between 2005 and 2009 by a Fourier Transform Infrared (FTIR) spectrometer, a Multifilter rotating shadow-band radiometer (MFRSR), a Cimel sunphotometer, a Global Positioning System (GPS) receiver, and daily radiosondes (Vaisala RS92). In addition we intercompare the water vapor profiles measured by the FTIR and the radiosondes. The long-term intercomparison assures that our study well represents the large water vapour variabilities that occur in the troposphere and allows a reliable empirical quality assessment for the different water vapour dataset. We examine how the data quality of the different techniques depends on atmospheric conditions and estimate the dry bias of the techniques which are restricted to clear sky observations.
Mineralogy of Iza Cave (Rodnei Mountains, N. Romania)  [cached]
Tamas Tudor,Kristaly Ferenc,Barbu-Tudoran Lucian
International Journal of Speleology , 2011,
Abstract: The secondary minerals from Iza Cave result from the interactions of karst water and/or cave atmosphere with a variety of sedimentaryand metamorphic rocks. The cave passages expose at various extents Eocene limestones and conglomerates, Oligocene blackshales, Upper Precambrian micaschists, marble and dolomitic marble and associated ore deposits. Twelve secondary mineralsidentified in the cave (carbonates, sulfates, phosphates, oxides and hydroxides, and silicates) are presented in this study. Calcite,aragonite, gypsum, brushite and hydroxylapatite are the components of common speleothems in the limestone, dolomite andconglomerate areas of the cave. Ankerite crusts are related to areas with pyrite mineralization within the metamorphic carbonaterocks. Goethite, jarosite, hematite and gypsum form various speleothems in the sectors within micaschists and conglomerates. Largeweathering deposits occurring in passage areas developed within micaschists consist of illite, kaolinite, jarosite, goethite, gypsumand alunite. The extent of the weathering deposits occurring on non-karst rocks in the underground environment makes this cave aparticularly interesting site for studies of water-rock interactions.
Orographic cirrus in a future climate  [PDF]
H. Joos,P. Spichtinger,U. Lohmann
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: A cloud resolving model (CRM) is used to investigate the formation of orographic cirrus clouds in the current and future climate. The formation of cirrus clouds depends on a variety of dynamical and thermodynamical processes, which act on different scales. First, the capability of the CRM in realistically simulating orographic cirrus clouds has been tested by comparing the simulated results to aircraft measurements of an orographic cirrus cloud. The influence of a warmer climate on the microphysical and optical properties of cirrus clouds has been investigated by initializing the CRM with vertical profiles of horizontal wind, potential temperature and equivalent potential temperature, respectively. The vertical profiles are extracted from IPCC A1B simulations for the current climate and for the period 2090–2099 for two regions representative for North and South America. The influence of additional moisture in a future climate on the propagation of gravity waves and the formation of orographic cirrus could be estimated. In a future climate, the increase in moisture dampens the vertical propagation of gravity waves and the occurring vertical velocities in the moist simulations. Together with higher temperatures fewer ice crystals nucleate homogeneously. Assuming that the relative humidity does not change in a warmer climate the specific humidity in the model is increased. This increase in specific humidity in a warmer climate results in a higher ice water content. The net effect of a reduced ice crystal number concentration and a higher ice water content is an increased optical depth. However, in some moist simulations dynamical changes contribute to changes in the ice water content, ice crystal number concentration and optical depth. For the corresponding dry simulations dynamical changes are more pronounced leading to a decreased optical depth in a future climate in some cases.
Iodine monoxide in the north subtropical free troposphere
O. Puentedura, M. Gil, A. Saiz-Lopez, T. Hay, M. Navarro-Comas, A. Gómez-Pelaez, E. Cuevas, J. Iglesias,L. Gomez
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: Iodine monoxide (IO) differential slant column densities (DSCD) have been retrieved from a new multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument deployed at the Iza a subtropical observatory as part of the Network for the Detection of Atmospheric Composition Change (NDACC) programme. The station is located at 2370 m a.s.l., well above the trade wind inversion that limits the top of the marine boundary layer, and hence is representative of the free troposphere. We report daily observations from May to August 2010 at different viewing angles. During this period, the spectral signature of IO was unequivocally detected on every day of measurement. A mean IO DSCD of 1.52×1013 molecules cm 2 was observed at the 5° instrument elevation angle (IEA) on clear days using a single zenith reference for the reported period, with a day-to-day variability of 33% at one standard deviation. Based on the simulation of the DSCDs using radiative transfer calculations with five different hypothesized IO profiles, the IO mixing ratio is estimated to range between 0.2 and 0.4 pptv in the free troposphere. Episodes of Saharan dust outbreaks were also observed, with large increases in the DSCDs at higher IEA, suggesting an enhancement of IO inside the dust cloud.
Physical controls on orographic cirrus inhomogeneity
J. E. Kay, M. Baker,D. Hegg
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2007,
Abstract: Optical depth distributions (P(σ)) are a useful measure of radiatively important cirrus (Ci) inhomogeneity. Yet, the relationship between P(σ) and underlying cloud physical processes remains unclear. In this study, we investigate the influence of homogeneous and heterogeneous freezing processes, ice particle growth and fallout, and mesoscale vertical velocity fluctuations on P(σ) shape during an orographic Ci event. We evaluate Lagrangian Ci evolution along kinematic trajectories from a mesoscale weather model (MM5) using an adiabatic parcel model with binned ice microphysics. Although the presence of ice nuclei increased model cloud cover, our results highlight the importance of homogeneous freezing and mesoscale vertical velocity variability in controlling Ci P(σ) shape along realistic upper tropospheric trajectories.
The physics of orographic gravity wave drag  [PDF]
Miguel A. Teixeira
Frontiers in Physics , 2014, DOI: 10.3389/fphy.2014.00043
Abstract: The drag and momentum fluxes produced by gravity waves generated in flow over orography are reviewed, focusing on adiabatic conditions without phase transitions or radiation effects, and steady mean incoming flow. The orographic gravity wave drag is first introduced in its simplest possible form, for inviscid, linearized, non-rotating flow with the Boussinesq and hydrostatic approximations, and constant wind and static stability. Subsequently, the contributions made by previous authors (primarily using theory and numerical simulations) to elucidate how the drag is affected by additional physical processes are surveyed. These include the effect of orography anisotropy, vertical wind shear, total and partial critical levels, vertical wave reflection and resonance, non-hydrostatic effects and trapped lee waves, rotation and nonlinearity. Frictional and boundary layer effects are also briefly mentioned. A better understanding of all of these aspects is important for guiding the improvement of drag parametrization schemes.
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