Variability of planetary-scale waves at mid-latitudes in the course of strat-warmings during DYANA

Summary This work investigates the variability of planetary-scale waves from motion field observations in the middle atmosphere carried out at the Budrio radar station near Bologna (45°N; 12°E) in the 1989–1990 winter during DYANA (DYnamics Adapted Network for the Atmosphere). Meso-thermospheric zonal winds associated with long-period waves give evidence of significant energy input from below mainly in the course of the two strat-warmings recorded at the end of January and in mid February 1990. Amplification of 10-day waves in the upper mesosphere and lower thermosphere just a few days before the temperature peak at the 10hPa stratospheric level, and the effects induced by these waves on tidal and mean fields, are here taken into account to clarify the influence and the evolution of strat-warmings in the middle atmosphere. Nonlinear mixing processes between planetary and tidal oscillations are indicated to be responsible for the short-term variability pointed out in the amplitude variations of tides.     

Atmospheric tides and periodic variations in the precipitation field

Summary The analysis of daily precipitation data at many weather stations in Alpes and Po Valley gives evidence of a “tidal” influence from luni-solar gravitational fields. Periodicities in the 13–15 and 27–30 day time interval have been frequently extracted from data series (ENEL data: 1970–1981 years; SMR data: 1961–1980 years), by using distinct methods. The tidal influence does not appear to be strictly constant with time, as the possible result of a modulation effect of luni-solar cycles having similar periods. Time variations of daily precipitation data as a function of some particular cycles show that gravitational tides affect heavy rainfalls more than mean precipitation values. The different contribution of “semi-monthly” oscillations with season underlines a more distinguishable regime of vertical motions in Winter with respect to Summer. In investigating joint effects of different luni-solar components, the inverse Fourier transform method points out superimposed influences in correspondence to some years (1966 and 1976), climatologically very interesting, and this might assist in the previsional studies of extreme precipitation.

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Riassunto I risultati delle analisi dei dati giornalieri di precipitazione, raccolti presso molte stazioni dell'arco alpino e della pianura padana (dati ENEL: anni 1970–1981 e dati SMR: anni 1961–1980) mettono in mostra un'influenza ?mareale? dei campi gravitazionali luni-solari. Anche utilizzando metodi distinti, è solitamente evidenziata la presenza di componenti periodiche nelle finestre temporali di 13–15 e 27–30 giorni. L'effetto mareale non appare rigidamente costante nel tempo, potendo risultare dalla modulazione di cicli luni-solari aventi periodi simili. Le variazioni nel tempo dei dati giornalieri di precipitazione in funzione di alcuni cicli particolari mostrano che l'influenza mareale ha un effetto maggiore sulle precipitazioni piú forti che non sui valori medi di precipitazione. Il diverso contributo di componenti ?semi-mensili? con la stagione sta ad indicare che l'azione di marea è meglio identificabile in inverno che non in estate. Nelle indagini sugli effetti congiunti di differenti componenti luni-solari, il metodo dell'antitrasformata di Fourier rivela influenze sovrapposte nel campo delle precipitazioni soprattutto in corrispondenza di alcuni anni particolarmente interessanti sotto il profilo climatologico (anni 1966 e 1976), e in tal senso questo metodo può essere utile in studi previsionali delle precipitazioni piú forti.

     

Evidence of internal gravity waves in the lower thermosphere at midlatitudes

Summary Wind measurements were made by the CNR Meteor Radar Station at Budrio (45°N, 12°E) in the April–September 1978 period in order to emphasize the role of internal gravity (IG) waves in the lower thermosphere ((80÷110) km). After briefly describing the basic properties of these waves, we determine some of their characteristics using both the conventional spectral-analysis methods and alternatively, for short-time data series, the maximum-entropy method (MEM). The Fourier analysis of these data indicates that the gravity waves with periods of 2<T<8 h have amplitudes increasing with height (up to (30÷40) ms⁻¹ at 100 km, in June), vertical wave-lengths of (8÷40) km and horizontal wave-lengths exceeding the corresponding ones by a factor of 50 or more. In May and September, by using the MEM method with a sampling of (10°20) min, gravity waves with periods of about 100 min and 2 h, respectively, have been tentatively identified. In August, the rates of energy loss per unit mass for internal gravity waves range from 0.015 to 0.045 W kg⁻¹ in the (80°100) km region and the momentum deposition by these waves is 2.4 m s⁻¹ h⁻¹ at 90 km. Under some specific conditions, the observed accelerations of the prevailing wind ((3÷4) m s⁻¹ d⁻¹) due to momentum deposition over a period of 4 consecutive days (24–27 August) may approach the above-calculated maximum value.

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Riassunto Misure di vento effettuate presso la Stazione Radar Meteorica del CNR di Budrio (45°N, 12°E) nel periodo aprile-settembre 1978 consentono di mettere in evidenza il ruolo delle onde interne di gravità (IG) nella bassa termosfera ((80÷110) km). Dopo aver descritto brevemente le proprietà basilari di tali onde, sono state determinate alcune loro caratteristiche facendo ricorso sia ai metodi tradizionali dell'analisi spettrale sia, in alternativa, per serie con un numero limitato di dati, al metodo della massima entropia (MEM). L'analisi di Fourier indica che le onde di gravità con periodo tra 2 e 8 ore hanno ampiezza crescente con l'altezza (fino a (30÷40) m s⁻¹ a 100 km in giugno), lunghezze d'onda verticali di (8÷40) km e orizzontali che superano le corrispondenti verticali di un fattore 50 o più. In maggio e settembre, facendo ricorso al metodo MEM e raggruppando i dati ogni (10÷20) min, sono state identificate, anche se non con sicurezza, onde di gravità con periodo rispettivamente di circa 100 min e di 2 ore. In agosto la perita di energia per unità di massa delle onde interne di gravità assume nella regione tra 80 e 100 km valori compresi tra 0.015 e 0.045 W kg⁻¹ e la quantità di moto trasferita da queste onde a 90 km è 2.4 m s⁻¹ per ora. In particolari condizioni le accelerazioni del vento prevalente ((3÷4) m s⁻¹ al giorno) osservate in seguito al trasferimento delle quantità di moto in un periodo di 4 giorni consecutivi (24–27 agosto) possono essere compatibili con il valore elevato calcolato in precedenza.

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Резюме Проведены измерения ветров с помощью CNR радарной станции атмосферных явлений в Будрио (45° N, 12° E) в период с апреля по сентябрь 1978, обращая особое внимание на роль внутренних гравитационных волн в нижней термосфере ((80÷110) км). После краткого описания основных свойств этих волн мы определяем некоторые характеристики этих волн, используя обычные методы спектрального анализа и для кратковременной последовательности данных метод максимальной энтропии. Фурье-анализ этих данных показывает что гравитационные волны с периодами 2<T<8 часов имеют амплитуды, увеличивающиеся с высотой (вплоть до (30÷40) мс⁻¹ на высоте 100 км, в июне), вертикальные длины волн (8÷40) км и горизонтальные длины волн, превьшающие соответствующие значения вертикальных в 50 или более раз. В мае и сентябре, используя метод максимальной энтропии с выборкой (10÷20) минут, были предварительно индентифицированы гравитационные волны с периодами соответственно около 100 минут и 2 часов. В августе интенсивность энергетических потерь на единицу массы для внутренних гравитационных волн составляла от 0.015 до 0.045 Вт кг⁻¹ в области (80÷100) км и ослабление импульса этих волн составляет 2.4 мс⁻¹ час⁻¹ на высоте 90 км. При некоторых специаляных условиях наблюденных ускорения преобладающих ветров ((3÷4) мс⁻¹ день⁻¹), из-за ослабления импулчса, в течение 4 последовательных дней (24–27 августа) могут достигать вышеуказанного максимального значения.

     

Katabatic winds in the lower Tamar Valley, Tasmania

Summary As an integral part of an air quality study undertaken in the lower Tamar Valley, Tasmania, where Bell Bay industrial area is located, 10-m surface winds were monitored by six Lambrecht Woelfle type anemographs along the valley between Low Head (near the coast) and Dilston (27km SE of Bell Bay industrial area) in 1982–1983. A tethered balloon was also used to investigate the temperature and wind profiles within the lowest 1 km of the atmosphere in the industrial area. This paper presents some of the results obtained. It mainly focuses on the katabatic winds which affect the dispersion of atmospheric emissions from various sources in the lower Tamar Valley, particularly those from the aluminium smelter, the ferro-alloys smelter, and the 2×120 MW oil-fired thermal power station, which are located in or near the industrial area. The characteristics of the katabatic winds are identified, and their implications for air pollution problems in the study area are discussed. In memory of Dr. R. Jones, foundation director of the Centre for Environmental Studies, the University of Tasmania, Australia. Paper presented at the GNFAO/EURASAP Meeting, Turin, September 1989. To speed up publication, proofs were not sent to the author and were supervised by the Scientific Committee.     

Remote sensing of thermal profile in the lower atmosphere by a radio-acoustic system

Summary A new radio-acoustic methodology, for the remote sensing of temperature profile in the lower troposphere, has been developed in the last few years. Since 1972 different types of radio-acoustic sounders have been designed and tested in the USA, Europe and Japan. The technique used for measurements in a Doppler tracking of a short acoustic pulse with a radar. Measurement of the sound speed as a function of delay from the start of the acoustic beam leads to the acquisition of the temperature vertical profile. After a brief review of the experimental radio-acoustic systems, the metric radio-acoustic sounder developed and tested at Istituto di Cosmogeofisica of the National Research Council (Italy) is analysed. Results of this sounder and its performance in fog-capping thermal inversion measurements are discussed. A comparison of the data measured with the radio-acoustic system and with traditional methods shows:a) sounder ability to produce vertical thermal profile with temperature accuracy and height discrimination comparable with conventional soundings;b) advantages typical of remote-sensing technique;c) applicability of the system both in assessing thermodynamic conditions in the planetary boundary layer (PBL) and in sensing conditions conductive to high concentrations of air pollutants at ground level. Preliminary results of the completely automatized system and application to air quality management are also presented. This work was partially supported by the Commission of the European Communities (CEC) under contract No. ENV·348 I(S) and by a research contract by ENEL-CRTN Milano.     

Amplification of synoptic vortices localized in the lower thermosphere

Joint Geophysics Committee, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 11, pp. 1315–1319, November, 1989.     

Preliminary results from the ozone lidar at the University of L''aquila

Summary We describe the ozone lidar operated at the Department of Physics of the University of L'Aquila. Preliminary ozone profiles obtained with the DIAL (differential absorption lidar) technique are also reported and a comparison is made with ECC (electro chemical cell) sonde data obtained at the FISBAT, CNR in Bologna. Although this comparison is of limited value the two sets of data show a good agreement. The influence of the recent detected volcanic aerosols from the eruption of Pinatubo on these measurements is also discussed.     

Ionospheric effect of the magnetospheric substorms at middle latitudes

Summary A study is made of theF2-layer effect of magnetospheric substorms over the Mediterranean area using data from several ionospheric stations for selected events in the current sunspot cycle 21. The night-time enhancements in the critical frequency of theF2-layer (f ₀ F2) and the total electron content (TEC) have been found with both premidnight and postmidnightf ₀ F2 peaks and a subsequent decrease in the minimum virtual height of theF region (h′F). It is found that the enhancements occur through the nights under steady geomagnetic conditions and that the time at which it is seen at Rome and Grocka ionospheric stations is progressively earlier as geomagnetic activity increases. It has been further shown that this type of thef ₀ F2 night-time increases is not always accompanied by an increase in TEC, although the reverse holds true during the nights of increased substorm activity. The fact that the considerable variability inf ₀ F2, TEC andh′F at the onset of the substorm expansion are preceded by the ionospheric dynamics associated with these observations can be very useful in the identification of precursor indicative of short-term variations of ionospheric propagation conditions.     

Analysis of solar-radiation characteristics at the EURELIOS power plant of Adrano

Summary Two years of experimental data, measured with high resolution at Adrano, have been analysed. The behaviour of the radiation changes on short time intervals, the cumulative distributions, the statistical properties and the influence of the integration time have been studied in detail. The distributions of daily collected energy in different periods andvs. power thresholds have been computed together with the differences between the average and the most favourable periods. In order to allow the optimum dimensioning of the storage system, a study on the statistical properties of excess (**) and recurrence time intervals has been developed. Work carried out under contract with the Italian Electricity Board (ENEL).     

Spectral analysis of wind speed determined at different sites in Sardinia

Summary A first evaluation of the characteristics of periodic fluctuations of the horizontal wind speed component at the ground has been determined in six stations in Sardinia. The analysis takes into account only wind speed component without considering variations in wind direction. The spectral analysis shows large variations in magnitudes from site to site and from season to season concerning the fundamental harmonic (24 hour) and the harmonics of periodT/2,T/3 andT/4. The largest fluctuations are associated with regimes of great windiness andvice versa.

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Riassunto Una prima valutazione delle caratteristiche delle fluttuazioni periodiche della componente orizzontale del vento a terra è stata effettuata prendendo in esame sei stazioni anemometriche situate in Sardegna. L'analisi spettrale ha messo in evidenza variazioni non trascurabili nelle ampiezze dell'armonica fondamentale (24 ore) della velocità del vento che dipendono dalla localizzazione delle stagioni e dalla stagione. In generale si può mettere in evidenza una relazione empirica che associa le ampiezze delle fluttuazioni con i valori medi stagionali della velocità del vento.

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Резюме На шести анемометрических станциях в Сардинии проведена первая оденка параметров периодических флуктуадий горизонтальной составляющей скорости ветра на поверхности Земли. Анализ учитывает только компоненту скорости ветра, не рассматвивая изменения направления ветра. Спектральный анализ обнаруживает большие изменения по амплитуде в зависимости от местоположения и от сезона при исследовании основной гармоники (24 часа) и гармоник с периодамиT/2,T/3 иT/4. Наибольшие флуктуации связаны с режимами сильного ветра и наоборот.

     

Incident short-wave radiation at the surface from meteosat data

Summary A physical model to estimate the incident short-wave radiation at the surface from satellite data has been improved, taking into account the effect of the aerosol scattering, and simplified, considering the surface albedo as a linear function of the planetary albedo. The model is applied to Meteosat-2 measurements for the Italian peninsula. Comparison with ground measurements uniformly distributed over Italy (14 stations) shows good agreement both for clear sky and for cloudy conditions. The r.m.s. error is approximately (8÷9)% considering all the data together. This work was developed during Dr. Marullo's stay as visiting scientist at the European Space Operations Center of ESA in Darmstadt, Germany.     

Measurements of climatic parameters and ground-level ozone at Terra Nova Bay in Antarctica

Summary The results of local meteorology, solar radiation and ground-level ozone measurements taken in Antarctica during the second Italian expedition (December 86–February 87) at Terra Nova Bay are presented. During the summer months the site of the Italian base camp is characterized by a thin strip of deglaciated ground, along which the temperature measurements close to the ground and up to 6 m high show a strongly superdiabatic profile. This irregular trend of the temperature in the surface layer is mainly due to the notable incoming amounts of radiation and to the extreme transparency of the atmosphere. This is also shown by the low values of the ratio between total radiation and diffuse radiation. The ground is thus subjected to intense heating, especially in the warmer hours of the day, while the surface layer of the atmosphere will be characterized by strong upward heat fluxes and by turbulent convective movements. Vertical-temperature-profile measurements show an almost forced persistence in the superdiabatic trend, which tends towards isothermic values only as a resultof rapid variations in the direction and intensity of the wind, connected to the downward flux of cold air masses, shown also by the simultaneous increases in ground-level ozone concentrations which would support the presence of dry-deposition processes in the lower layer. However, the complex local orography and the horizontal discontinuity (sea, deglaciated coast, snow-covered surfaces) do not permit a correct application of profile flux relations, normally used in studies on groundlevel dry-deposition. Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome.     

Ozone deficiency and deficit recovery time at Ispra in 1993 with respect to 1992

Summary Total ozone values measured at Ispra, Italy (45⁰48′ latitude, −8⁰37′ longitude) by a Brewer station during 1992 and 1993 have been compared. The time required in 1993 by ozone to recover the level of the previous year lasted up to the end of July, while for 1992 the recovery to reference ozone values obtained by averaging thirty years of data (1957–1986) taken at Arosa (Switzerland) was about three months shorter. For the first six months of 1993, a mean ozone deficit of the order of 4% with respect to the value for the same period of 1992 has been calculated. An analysis of the UV data taken together with ozone confirmed the anomalous behaviour of ozone in the first half-year of 1993.     

Climatological study of air trajectories arriving at three alpine sites

Summary Within the frame of the EUROTRAC project and in collaboration with ENEL/C.R.T.N. of Milan, a research activity aiming at a meteorological interpretation of smaples of trace chemical compounds collected in alpine glaciers started. With reference to that, availing ourselves of a wind data set coming from the ECMWF analysis, backward air trajectories arriving at three alpine sites six hours for five years (1981–1985) have been computed. The origin of the trajectories at various distances has been evidentiated through their partition in sectors and in altitude.     

A study of greenhouse gases and air trajectories at Plateau Rosa

Summary The attention paid to changes in atmospheric concentrations of greenhouse gases has recently increased, with particular regard to the relationships between variations of their annual trends and of their shorter-period fluctuations on the one hand, and some geophysical and biological natural processes (like atmospheric transport, volcanic eruptions, ENSO events, seasonal vegetation cycles, and so on) on the other hand. Careful analysis and interpretation of the above relationships, in fact, can often disclose unknown mechanisms acting on modulations of these gases and make it possible for us to better understand the contributions made to them by natural causes, contrasted with anthropogenic ones. This paper presents and discusses the results of a series of CO₂ air concentration data, measured at Plateau Rosa (3480 m a.s.l.—Italian Western Alps) over a period of about four years, and correlated with atmospheric transport processes on synoptic scale. These results have shown the leading role played by some kinds of atmospheric circulation patterns in creating situations of not fully mixed air streams (and, as such, not representative of background conditions) and have also suggested a ?meteorological? selection scheme for CO₂ data to be used in evaluating more reliable annual trends.     

Spectral analysis and trend of total ozone observations at Vigna di Valle

Summary Time series analyses of measurements of total ozone make possible an in-depth climatological study of this important stratospheric gas. The Italian Air Force's Vigna di Valle Observatory (42°N, 12°E, 262 m a.s.l.) provided a time series of monthly averages (January 1958–December 1988) of total ozone. Spectral analysis and running averages were combined to detect medium-(QBOs of estimated (4÷5) DU amplitudes) and long-term fluctuations (possible correlation to 11-year solar cycle) and to filter them, leaving any overlapping trends unaltered. Total ozone trend estimates produced by the present study were +0.1% per decade for the 1959–1987 period and a decrease of −0.4% per decade for the more recent 1970–1987 span, over which a pronounced ozone depletion caused mainly by CFCs is assumed. This study has supported by the CNR-ENEL Project ?Interaction of energy system with human health and environment?.     

Analysis of pyrheliometric measurements at Modena (Italy) from 1990 to 1991

Summary During the last few years continuous measurements of direct solar irradiance have been taken in Modena (37 m. a.s.l.) using pyrheliometers with three filters (quartz filters, OG51, RG61). The apparent atmospheric transmission calculated using the so-called rationing technique can be utilised as a useful parameter to monitor the atmosphere. Preliminary results suggest that the atmospheric transmission seems be able to highlight meteorological events such as the transport of dust.     

Thirteen years of atmospheric carbon dioxide measurements at Mt. Cimone station, Italy

Summary The atmospheric carbon dioxide concentration has been continuously measured at Mt. Cimone station from March 1979. In this paper a selection scheme is applied to the measured concentrations in order to obtain data representative of background conditions. Monthly averages, expressed in the WMO X-85 scale are calculated from the selected data and analysed by a technique of time series decomposition until december 1991. Monthly values exibit an increasing long-term trend, mainly due to the fossil fuel combustion: over the whole monitoring period the average CO₂ growth rate is 1.66 p.p.m.v./y. A seasonal cycle, largely due to the biospheric activity of the northern hemisphere is evident. The estimated average peak-to-peak amplitude is 11.32 p.p.m.v. with a maximum occurring in April and a minimum in August. The seasonal amplitude is found to be decreasing with time, by about 1.5 p.p.m.v. over the entire record: no conclusive interpretations are given about this experimental result. Besides the long-term trend and the seasonal cycle, CO₂ interannual variations are observed in the selected record; these correlate negatively with the Southern Oscillation Index (SOI) with a maximum correlation coefficient of 0.6 for a delay of about 7–8 months.