1. Introduction In the framework of the European Association of Scientists in Environmental Pollu... more 1. Introduction In the framework of the European Association of Scientists in Environmental Pollution (EURASEP) project and now in the Coastal Transport of Pollutants Activity, the Joint Research Center of the European Communities has made considerable effort, both ex-perimental ...
The topside part of the ionosphere lies above the ionospheric F2 layer peak and extends up to the... more The topside part of the ionosphere lies above the ionospheric F2 layer peak and extends up to the plasmasphere. Since it contains a considerable part of the ionospheric plasma, its modeling is important for telecommunication\u2019s purposes. In this work, electron density values recorded by Langmuir Probes on board the Swarm constellation are used as top anchor points by definite analytical functions (\u3b1-Chapman, \u3b2-Chapman, Epstein and Exponential) to investigate the variability of the topside plasma scale height H, a parameter which is crucial to perform a reliable modeling of the topside ionosphere. Bottom anchor points are provided by the IRIUP (International Reference Ionosphere UPdate) method, which is a method developed to update the IRI model relying on the assimilation of foF2 and M(3000)F2 data routinely recorded by a network of ionosonde stations. The IRIUP method calculates updated effective indices IG12eff and R12eff at each station of the network and, applying a universal Kriging method, generates maps of these indices which are then used to update the IRI output in terms of foF2 and hmF2. The height and electron density values of both top and bottom anchor points are used to obtain the H value, by means of a minimization procedure, making use of each of the aforementioned four topside analytical functions. The reliability of this approach is based on the hypothesis that H at heights around the F2 layer peak and for the first hundreds kilometers above is nearly constant, being this region dominated by O+ ions and with a temperature nearly constant. H values are statistically evaluated to look for any relevant relation with foF2 and hmF2. Moreover, a statistical comparison with COSMIC radio occulation profiles is carried out to asses which analytical profile function is the best one to represent the topside ionospheric profile, making use of the modelled H values
This work describes several important improvements made to the International Reference Ionosphere... more This work describes several important improvements made to the International Reference Ionosphere UPdate (IRI UP) method, and a careful validation of its performances under disturbed conditions. The IRI UP method has been improved developing an algorithm capable to properly filter wrongly autoscaled ionosonde data to be assimilated, avoiding the use of these in the assimilation process. Furthermore, the preliminary quality check used to choose the variogram model in the Universal Kriging method has been replaced with a new quality check routine (NQCR), based on statistical tests carried out using the variables Q 1 , Q 2 , and cR, built on variogram's residuals. NQCR objectively identifies the best variogram model from which to get more reliable effective indices maps to be ingested in the IRI model to obtain updated foF2 and hmF2 maps. IRI UP has been applied on 30 different time intervals, between January 1, 2004, and December 31, 2016, characterized by moderate, strong, and severe geomagnetic conditions, over the European region. A statistical comparison between IRI UP and IRI at the truth sites located at Fairford (51.7°N, 1.5°W, UK) and San Vito (40.6°N, 17.8°E, Italy), for foF2 and hmF2, has been performed. From the statistical validation clearly emerges how IRI UP, for foF2, performs significantly better than IRI, for each of the 30 geomagnetic storms considered. Regarding hmF2, IRI UP performances are lower than those for foF2, although still better than IRI ones. In the light of the results achieved in this investigation, the IRI UP method represents an interesting approach to Space Weather forecast in the ionospheric domain.
A method to real-time update the IRI model through data assimilated by a European ionosonde netwo... more A method to real-time update the IRI model through data assimilated by a European ionosonde network is proposed, described and statistically evaluated under a severe geomagnetic event (the St.Patrick storm occurred on March 17 2015), comparing the corresponding output with the ones by IRI and IRTAM models. This method, called IRI UP (International Reference Ionosphere UPdate), relies on the foF2 and M(3000)F2 ionospheric characteristics routinely recorded by a network of 12 European ionosonde stations. The real-time assimilated data are used to calculate updated IRI's indices and (identified as and ) for every station's point, that are used to calculate maps of these indices through the universal Kriging method. Five variogram models are used and statistically tested to verify which of these perform better for each effective index. Maps of these updated indices are used as input for the IRI model, which gives as output updated values of foF2 and hmF2. In order to evaluate the ability of the proposed method to catch fast-time and small-scale changes that are usual under disturbed conditions, statistical quantities are calculated for two test stations (not considered in the assimilation process), Fairford and San Vito, for the IRI model with the STORM option set to on, and for IRI UP and for IRTAM methods. The method here proposed turns out to be very effective, with significant improvements regarding foF2 characteristic and slight improvements for hmF2. Important improvements have been verified also for quiet and moderate disturbed conditions.
During the Antarctic summer 1994r95 the values of downward and upward flux densities of both sola... more During the Antarctic summer 1994r95 the values of downward and upward flux densities of both solar and terrestrial radiation were recorded at 1200 m for a period of 1 month on the Reeves Ž X X .
Atmospheric Chemistry and Physics Discussions, 2018
Far-infrared (FIR: 100 cm-1 < wavenumber, ν < 667 cm-1) radiation emitted by the Earth and its at... more Far-infrared (FIR: 100 cm-1 < wavenumber, ν < 667 cm-1) radiation emitted by the Earth and its atmosphere plays a key role in the Earth's energy budget. However, because of a lack of spectrally resolved measurements, radiation schemes in climate models suffer from a lack of constraint across this spectral range. Exploiting a method developed to estimate upwelling far-infrared radiation from mid-infrared (MIR: 667 cm-1 < ν < 1400 cm-1) observations, we explore the possibility of inferring zenith FIR downwelling radiances in zenith-looking observation geometry, focusing on clear-sky conditions in Antarctica. The methodology selects a MIR predictor wavenumber for each FIR wavenumber based on the maximum correlation seen between the different spectral ranges. Observations from the REFIR-PAD instrument (Radiation Explorer in the Far Infrared-Prototype for Application and Development) and high resolution radiance simulations generated from co-located radio soundings are used to develop and assess the method. We highlight the impact of noise on the correlation between MIR and FIR radiances by comparing the observational and theoretical cases. Using the observed values in isolation, between 150 and 360 cm-1 , differences between the 'true' and 'extended' radiances are less than 5 %. However, in spectral bands of low signal, between 360 and 667 cm-1 , the impact of instrument noise is strong and increases the differences seen. When the extension of the observed spectra is performed using regression coefficients based on noise-free radiative-transfer simulations the results show strong biases, exceeding 100 % where the signal is low. These biases are reduced to just a few percent if the noise in the observations is accounted for the simulation procedure. Our results imply that while it is feasible to use this type of approach to extend mid infrared spectral measurements to the far-infrared, the quality of the extension will be strongly dependent on the noise characteristics of the observations. A good knowledge of the atmospheric state associated with the measurements is also required in order to build a representative regression model. 1 Introduction Defined here as wavelengths above 15 µm or wavenumbers below 667 cm-1 , the far-infrared (FIR) spectral band plays a key role in energetic exchanges between the Earth's surface, atmosphere and space (Harries et al., 2008). Under clear-sky conditions, absorption in the FIR is dominated by water vapour such that typically very little FIR radiation emitted from the surface directly
During the Antarctic summer 1994r95 the values of downward and upward flux densities of both sola... more During the Antarctic summer 1994r95 the values of downward and upward flux densities of both solar and terrestrial radiation were recorded at 1200 m for a period of 1 month on the Reeves Ž X X .
2014 Il existe de nombreuses méthodes pour calculer le spectre instantané de la radiance dans le ... more 2014 Il existe de nombreuses méthodes pour calculer le spectre instantané de la radiance dans le cas d'un ciel serein. Ces méthodes nécessitent la connaissance de quelques paramètres atmosphériques comme la turbidité, l'épaisseur optique de la vapeur d'eau et de l'ozone. Toutefois, pour de nombreuses applications, il est plus utile de connaître le spectre moyen sur une longue période. Dans cet article nous introduisons et analysons une méthode simplifiée pour calculer la radiance spectrale moyenne avec une erreur inférieure à 2 %. Nous analysons, entre autre la dépendance de la radiance spectrale moyenne journalière des paramètres atmosphériques et saisonniers (c'est-à-dire de la masse d'air). Abstract. 2014 There are several models to compute instantaneous clear sky solar radiation and they require the precise knowledge of meteorologically relevant parameters as the turbidity and the optical thickness of water vapour and ozone. However, in many cases only a mean radiance spectrum is wanted. In this paper we introduce and analyse a simplified method which permits to calculate the daily average radiance spectrum with an error less than 2 %. The dependence of the daily radiance spectrum on the atmospheric parameters and on the season is also analysed.
A first comparison is presented between measured and computed spectral sky irradiance. The comput... more A first comparison is presented between measured and computed spectral sky irradiance. The computations are done using a model developed by Sobolev. From the comparison it appears that the pattern of calculated irradiance is quite similar to the measured one in the half-hemisphere containing the sun while discrepancies are evident in the opposite half-hemisphere and at large zenith angles.
1. Introduction In the framework of the European Association of Scientists in Environmental Pollu... more 1. Introduction In the framework of the European Association of Scientists in Environmental Pollution (EURASEP) project and now in the Coastal Transport of Pollutants Activity, the Joint Research Center of the European Communities has made considerable effort, both ex-perimental ...
The topside part of the ionosphere lies above the ionospheric F2 layer peak and extends up to the... more The topside part of the ionosphere lies above the ionospheric F2 layer peak and extends up to the plasmasphere. Since it contains a considerable part of the ionospheric plasma, its modeling is important for telecommunication\u2019s purposes. In this work, electron density values recorded by Langmuir Probes on board the Swarm constellation are used as top anchor points by definite analytical functions (\u3b1-Chapman, \u3b2-Chapman, Epstein and Exponential) to investigate the variability of the topside plasma scale height H, a parameter which is crucial to perform a reliable modeling of the topside ionosphere. Bottom anchor points are provided by the IRIUP (International Reference Ionosphere UPdate) method, which is a method developed to update the IRI model relying on the assimilation of foF2 and M(3000)F2 data routinely recorded by a network of ionosonde stations. The IRIUP method calculates updated effective indices IG12eff and R12eff at each station of the network and, applying a universal Kriging method, generates maps of these indices which are then used to update the IRI output in terms of foF2 and hmF2. The height and electron density values of both top and bottom anchor points are used to obtain the H value, by means of a minimization procedure, making use of each of the aforementioned four topside analytical functions. The reliability of this approach is based on the hypothesis that H at heights around the F2 layer peak and for the first hundreds kilometers above is nearly constant, being this region dominated by O+ ions and with a temperature nearly constant. H values are statistically evaluated to look for any relevant relation with foF2 and hmF2. Moreover, a statistical comparison with COSMIC radio occulation profiles is carried out to asses which analytical profile function is the best one to represent the topside ionospheric profile, making use of the modelled H values
This work describes several important improvements made to the International Reference Ionosphere... more This work describes several important improvements made to the International Reference Ionosphere UPdate (IRI UP) method, and a careful validation of its performances under disturbed conditions. The IRI UP method has been improved developing an algorithm capable to properly filter wrongly autoscaled ionosonde data to be assimilated, avoiding the use of these in the assimilation process. Furthermore, the preliminary quality check used to choose the variogram model in the Universal Kriging method has been replaced with a new quality check routine (NQCR), based on statistical tests carried out using the variables Q 1 , Q 2 , and cR, built on variogram's residuals. NQCR objectively identifies the best variogram model from which to get more reliable effective indices maps to be ingested in the IRI model to obtain updated foF2 and hmF2 maps. IRI UP has been applied on 30 different time intervals, between January 1, 2004, and December 31, 2016, characterized by moderate, strong, and severe geomagnetic conditions, over the European region. A statistical comparison between IRI UP and IRI at the truth sites located at Fairford (51.7°N, 1.5°W, UK) and San Vito (40.6°N, 17.8°E, Italy), for foF2 and hmF2, has been performed. From the statistical validation clearly emerges how IRI UP, for foF2, performs significantly better than IRI, for each of the 30 geomagnetic storms considered. Regarding hmF2, IRI UP performances are lower than those for foF2, although still better than IRI ones. In the light of the results achieved in this investigation, the IRI UP method represents an interesting approach to Space Weather forecast in the ionospheric domain.
A method to real-time update the IRI model through data assimilated by a European ionosonde netwo... more A method to real-time update the IRI model through data assimilated by a European ionosonde network is proposed, described and statistically evaluated under a severe geomagnetic event (the St.Patrick storm occurred on March 17 2015), comparing the corresponding output with the ones by IRI and IRTAM models. This method, called IRI UP (International Reference Ionosphere UPdate), relies on the foF2 and M(3000)F2 ionospheric characteristics routinely recorded by a network of 12 European ionosonde stations. The real-time assimilated data are used to calculate updated IRI's indices and (identified as and ) for every station's point, that are used to calculate maps of these indices through the universal Kriging method. Five variogram models are used and statistically tested to verify which of these perform better for each effective index. Maps of these updated indices are used as input for the IRI model, which gives as output updated values of foF2 and hmF2. In order to evaluate the ability of the proposed method to catch fast-time and small-scale changes that are usual under disturbed conditions, statistical quantities are calculated for two test stations (not considered in the assimilation process), Fairford and San Vito, for the IRI model with the STORM option set to on, and for IRI UP and for IRTAM methods. The method here proposed turns out to be very effective, with significant improvements regarding foF2 characteristic and slight improvements for hmF2. Important improvements have been verified also for quiet and moderate disturbed conditions.
During the Antarctic summer 1994r95 the values of downward and upward flux densities of both sola... more During the Antarctic summer 1994r95 the values of downward and upward flux densities of both solar and terrestrial radiation were recorded at 1200 m for a period of 1 month on the Reeves Ž X X .
Atmospheric Chemistry and Physics Discussions, 2018
Far-infrared (FIR: 100 cm-1 < wavenumber, ν < 667 cm-1) radiation emitted by the Earth and its at... more Far-infrared (FIR: 100 cm-1 < wavenumber, ν < 667 cm-1) radiation emitted by the Earth and its atmosphere plays a key role in the Earth's energy budget. However, because of a lack of spectrally resolved measurements, radiation schemes in climate models suffer from a lack of constraint across this spectral range. Exploiting a method developed to estimate upwelling far-infrared radiation from mid-infrared (MIR: 667 cm-1 < ν < 1400 cm-1) observations, we explore the possibility of inferring zenith FIR downwelling radiances in zenith-looking observation geometry, focusing on clear-sky conditions in Antarctica. The methodology selects a MIR predictor wavenumber for each FIR wavenumber based on the maximum correlation seen between the different spectral ranges. Observations from the REFIR-PAD instrument (Radiation Explorer in the Far Infrared-Prototype for Application and Development) and high resolution radiance simulations generated from co-located radio soundings are used to develop and assess the method. We highlight the impact of noise on the correlation between MIR and FIR radiances by comparing the observational and theoretical cases. Using the observed values in isolation, between 150 and 360 cm-1 , differences between the 'true' and 'extended' radiances are less than 5 %. However, in spectral bands of low signal, between 360 and 667 cm-1 , the impact of instrument noise is strong and increases the differences seen. When the extension of the observed spectra is performed using regression coefficients based on noise-free radiative-transfer simulations the results show strong biases, exceeding 100 % where the signal is low. These biases are reduced to just a few percent if the noise in the observations is accounted for the simulation procedure. Our results imply that while it is feasible to use this type of approach to extend mid infrared spectral measurements to the far-infrared, the quality of the extension will be strongly dependent on the noise characteristics of the observations. A good knowledge of the atmospheric state associated with the measurements is also required in order to build a representative regression model. 1 Introduction Defined here as wavelengths above 15 µm or wavenumbers below 667 cm-1 , the far-infrared (FIR) spectral band plays a key role in energetic exchanges between the Earth's surface, atmosphere and space (Harries et al., 2008). Under clear-sky conditions, absorption in the FIR is dominated by water vapour such that typically very little FIR radiation emitted from the surface directly
During the Antarctic summer 1994r95 the values of downward and upward flux densities of both sola... more During the Antarctic summer 1994r95 the values of downward and upward flux densities of both solar and terrestrial radiation were recorded at 1200 m for a period of 1 month on the Reeves Ž X X .
2014 Il existe de nombreuses méthodes pour calculer le spectre instantané de la radiance dans le ... more 2014 Il existe de nombreuses méthodes pour calculer le spectre instantané de la radiance dans le cas d'un ciel serein. Ces méthodes nécessitent la connaissance de quelques paramètres atmosphériques comme la turbidité, l'épaisseur optique de la vapeur d'eau et de l'ozone. Toutefois, pour de nombreuses applications, il est plus utile de connaître le spectre moyen sur une longue période. Dans cet article nous introduisons et analysons une méthode simplifiée pour calculer la radiance spectrale moyenne avec une erreur inférieure à 2 %. Nous analysons, entre autre la dépendance de la radiance spectrale moyenne journalière des paramètres atmosphériques et saisonniers (c'est-à-dire de la masse d'air). Abstract. 2014 There are several models to compute instantaneous clear sky solar radiation and they require the precise knowledge of meteorologically relevant parameters as the turbidity and the optical thickness of water vapour and ozone. However, in many cases only a mean radiance spectrum is wanted. In this paper we introduce and analyse a simplified method which permits to calculate the daily average radiance spectrum with an error less than 2 %. The dependence of the daily radiance spectrum on the atmospheric parameters and on the season is also analysed.
A first comparison is presented between measured and computed spectral sky irradiance. The comput... more A first comparison is presented between measured and computed spectral sky irradiance. The computations are done using a model developed by Sobolev. From the comparison it appears that the pattern of calculated irradiance is quite similar to the measured one in the half-hemisphere containing the sun while discrepancies are evident in the opposite half-hemisphere and at large zenith angles.
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Papers by Rolando Rizzi