Mirela Voiculescu

Estimating Annual CO2 Flux for Lutjewad Station Using Three Different Gap-Filling Techniques

Long-term measurements of CO2 flux can be obtained using the eddy covariance technique, but these datasets are affected by gaps which hinder the estimation of robust long-term means and annual ecosystem exchanges. We compare results obtained using three gap-fill techniques: multiple regression (MR), multiple imputation (MI), and artificial neural networks (ANNs), applied to a one-year dataset of hourly CO2 flux measurements collected in Lutjewad, over a flat agriculture area near the Wadden Sea dike in the north of the Netherlands. The dataset was separated in two subsets: a learning and a validation set. The performances of gap-filling techniques were analysed by calculating statistical criteria: coefficient of determination (R 2), root mean square error (RMSE), mean absolute error (MAE), maximum absolute error (MaxAE), and mean square bias (MSB). The gap-fill accuracy is seasonally dependent, with better results in cold seasons. The highest accuracy is obtained using ANN technique which is also less sensitive to environmental/seasonal conditions. We argue that filling gaps directly on measured CO2 fluxes is more advantageous than the common method of filling gaps on calculated net ecosystem change, because ANN is an empirical method and smaller scatter is expected when gap filling is applied directly to measurements.

Different response of clouds to solar input

[1] There is evidence that solar activity variations can affect the cloud cover at Earth. However, it is still unclear which solar driver plays the most important role in the cloud formation. Here we use partial correlations to distinguish between the effects of two solar drivers (cosmic rays and the UV irradiance) and the mutual relations between clouds at different altitudes. We find that the solar influence on cloud cover is not uniquely defined by one solar driver, but both seem to play a role depending on the climatic conditions and altitude. In particular, low clouds are mostly affected by UV irradiance over oceans and dry continental areas and by cosmic rays over some mid-high latitude oceanic areas and moist lands with high aerosol concentration. High clouds respond more strongly to cosmic ray variations, especially over oceans and moist continental areas. These results provide observational constraints on related climate models. Citation: Voiculescu, M., I. G. Usoskin, and K. Mursula (2006), Different response of clouds to solar input, Geophys. Res. Lett., 33, L21802, doi:10.1029/2006GL027820.

Persistent solar signatures in cloud cover: spatial and temporal analysis

A consensus regarding the impact of solar variability on cloud cover is far from being reached. Moreover, the impact of cloud cover on climate is among the least understood of all climate components. This motivated us to analyze the persistence of solar signals in cloud cover for the time interval 1984‐2009, covering two full solar cycles. A spatial and temporal investigation of the response of low, middle and high cloud data to cosmic ray induced ionization (CRII) and UV irradiance (UVI) is performed in terms of coherence analysis of the two signals. For some key geographical regions the response of clouds to UVI and CRII is persistent over the entire time interval indicating a real link. In other regions, however, the relation is not consistent, being intermittent or out of phase, suggesting that some correlations are spurious. The constant in phase or anti-phase relationship between clouds and solar proxies over some regions, especially for low clouds with UVI and CRII, middle clouds with UVI and high clouds with CRII, definitely requires more study. Our results show that solar signatures in cloud cover persist in some key climate-defining regions for the entire time period and supports the idea that, if existing, solar effects are not visible at the global level and any analysis of solar effects on cloud cover (and, consequently, on climate) should be done at the regional level.

The 3D model of the plasmasphere coupled to the ionosphere

Pierrard and Stegen (2008) has been coupled with the ionospheric IRI model. In addition to the electron number density, the plasmaspheric model is also developed to include the temperature profiles of the different particles and ion composition at altitudes from 60 to 2000 km. Results of the model for the F region trough are compared with coincident observations of middle and top ionosphere by means of satellite tomography and radar measurements. A good match between the model and observations supports the idea that the present model is useful for investigating physical mechanism involved in the plasmasphere‐ionosphere coupling and for acquiring information about the plasmaspheric behaviour based on ionospheric observations

Clouds blown by the solar wind

In this letter we investigate possible relationships between the cloud cover (CC) and the interplanetary electric field (IEF), which is modulated by the solar wind speed and the interplanetary magnetic field. We show that CC at mid‐high latitudes systematically correlates with positive IEF, which has a clear energetic input into the atmosphere, but not with negative IEF, in general agreement with predictions of the global electric circuit (GEC)-related mechanism. Thus, our results suggest that mid‐high latitude clouds might be affected by the solar wind via the GEC. Since IEF responds differently to solar activity than, for instance, cosmic ray flux or solar irradiance, we also show that such a study allows distinguishing one solar-driven mechanism of cloud evolution, via the GEC, from others.

Study of Physico-Chemical Characteristics of Wastewater in an Urban Agglomeration in Romania

This study investigates the level of wastewater pollution by analyzing its chemical characteristics at five wastewater collectors. Samples are collected before they discharge into the Danube during a monitoring campaign of two weeks. Organic and inorganic compounds, heavy metals, and biogenic compounds have been analyzed using potentiometric and spectrophotometric methods. Experimental results show that the quality of wastewater varies from site to site and it greatly depends on the origin of the wastewater. Correlation analysis was used in order to identify possible relationships between concentrations of various analyzed parameters, which could be used in selecting the appropriate method for wastewater treatment to be implemented at wastewater plants.

Measurements of Tropospheric NO2 in Romania Using a Zenith-Sky Mobile DOAS System and Comparisons with Satellite Observations

In this paper we present a new method for retrieving tropospheric NO2 Vertical Column Density (VCD) from zenith-sky Differential Optical Absorption Spectroscopy (DOAS) measurements using mobile observations. This method was used during three days in the summer of 2011 in Romania, being to our knowledge the first mobile DOAS measurements peformed in this country. The measurements were carried out over large and different areas using a mobile DOAS system installed in a car. We present here a step-by-step retrieval of tropospheric VCD using complementary observations from ground and space which take into account the stratospheric contribution, which is a step forward compared to other similar studies. The detailed error budget indicates that the typical uncertainty on the retrieved NO2tropospheric VCD is less than 25%. The resulting ground-based data set is compared to satellite measurements from the Ozone Monitoring Instrument (OMI) and the Global Ozone Monitoring Experiment-2 (GOME-2). For instance, on 18 July 2011, in an industrial area located at 47.03°N, 22.45°E, GOME-2 observes a tropospheric VCD value of (3.4 ± 1.9) × 1015 molec./cm2, while average mobile measurements in the same area give a value of (3.4 ± 0.7) × 1015 molec./cm2. On 22 August 2011, around Ploiesti city (44.99°N, 26.1°E), the tropospheric VCD observed by satellites is (3.3 ± 1.9) × 1015 molec./cm2 (GOME-2) and (3.2 ± 3.2) × 1015 molec./cm2 (OMI), while average mobile measurements give (3.8 ± 0.8) × 1015 molec./cm2. Average ground measurements over “clean areas”, on 18 July 2011, give (2.5 ± 0.6) × 1015 molec./cm2 while the satellite observes a value of (1.8 ± 1.3) × 1015 molec./cm2.

Radar observations of simultaneous traveling ionospheric disturbances and atmospheric gravity waves

Simultaneous observations of atmospheric gravity waves (AGWs) and traveling ionospheric disturbances (TIDs) measured by an incoherent scatter radar at high latitudes are shown. The measurements were made using a beam swing experiment of the EISCAT UHF radar. The F region TID is seen as wavefronts in electron density, whereas the E region AGW is seen in the oscillations of the neutral wind. The wave vector of the TID has a downward component indicating that energy propagates upward. The periods of AGWs and TIDs are approximately the same (52–57min), so it is concluded that the observed gravity wave in the E region propagates to the F region causing the TID there. Two interesting properties of the waves are observed. First, the neutral wind oscillations have an amplitude minimum at about 115km. It is suggested that this could be related to the minimum of the vertical refractive index around 120km. Second, in the course of time, the wave vector of the TID turns more in the downward direction, which leads to an increase in the horizontal wave length from 400 to 1450km. A possible explanation is that the background wind increases with altitude and turns the wavefronts more horizontal when distance from a stationary source increases. We suggest that the source is the sunrise terminator, since the horizontal direction of propagation of the TID in the morning hours is from the west, where both the auroral and thunderstorm activity are low.

Satellite Observations of NO2 Trend over Romania

Satellite-based measurements of atmospheric trace gases loading give a realistic image of atmospheric pollution at global, regional, and urban level. The aim of this paper is to investigate the trend of atmospheric NO2 content over Romania for the period 1996–2010 for several regions which are generally characterized by different pollutant loadings, resulting from GOME-1, SCIAMACHY, OMI, and GOME-2 instruments. Satellite results are then compared with ground-based in situ measurements made in industrial and relatively clean areas of one major city in Romania. This twofold approach will help in estimating whether the trend of NO2 obtained by means of data satellite retrievals can be connected with the evolution of national industry and transportation.

Modeling results of atmospheric dispersion of NO2 in an urban area using METI-LIS and comparison with coincident mobile DOAS measurements

Synergetic use of in–situ measurements, remote sensing observations and model simulations can provide valuable information about atmospheric chemistry and air quality. In this work we present for the first time a qualitative comparison between modeled NO2 concentrations at ground level using dispersion model METI–LIS and tropospheric NO2 columns obtained by mobile DOAS technique. Experimental and modeling results are presented for a Romanian city, Braila (45.26 ° N, 27.95 ° E). In–situ observations of NO2 and meteorological data from four ground stations belonging to the local environmental agency were used to predict the concentration of NO2 at ground level by atmospheric dispersion modeling on two days when mobile DOAS measurements were available. The mobile DOAS observations were carried out using a UV–VIS spectrometer mounted on board a car. The tropospheric Vertical Column Density (VCD) of NO2 is deduced from DOAS observations. The VCD was obtained using complementary ground and space observations. The correlation between model and DOAS observations is described by a correlation coefficient of 0.33. Also, model results based on averaged in–situ measurements for a period of 5 years (2008–2012) are used for an overview of the background NO2 evolution in time and space for the selected urban area.