Network to cell contrast at microwaves     

F. Chiuderi Drago  M. R. Kundu  E. J. Schmahl 《Solar physics》1983,85(2):237-242

Using different models deduced from EUV lines for the cell and for various network components, the corresponding radio brightness temperature in the millimetric and centimetric range of wavelengths are computed. The contrast C = [T _b (network)]/[T _b (cell)] and the difference ΔT = T _b (network) - T _b (cell) are compared with the few available observations of the quiet Sun inhomogeneities performed with sufficient angular resolution. The comparison shows a satisfactory agreement with most of the observations.  相似文献   

Microwave,Soft and Hard X-Ray Observations of Solar Flares – a Self-Consistent Model of the Flare Site     

Chiuderi Drago  F.  Alissandrakis  C.E.  Bentley  R.D.  Philips  A.T. 《Solar physics》1998,182(2):459-476

High-resolution microwave observations of several flares performed with the Westerbork Synthesis Radio Telescope (WRST) on 3 and 4 July 1993 are compared with Yohkoh observations in the soft and hard X-ray domain. Only for one flare, among the six analyzed, was the hard X-ray spectrum between 20 and 200 keV available from the Wide Bragg Spectrometer, supplying the energy spectrum of non-thermal particles responsible for this radiation and for the radio emission. A complete model of this flare is derived which accounts for all available observations in the X-ray and radio wavelengths.  相似文献   

Microwave emission above steady and moving sunspots     

F. Chiuderi Drago  C. Alissandrakis  M. Hagyard 《Solar physics》1987,112(1):89-105

Two-dimensional maps of radio brightness temperature and polarization, computed assuming thermal emission with free-free and gyroresonance absorption, are compared with observations of active region 2502, performed at Westerbork at λ = 6.16 cm during a period of 3 days in June 1980. The computation is done assuming a homogeneous model in the whole field of view (5′ × 5′) and a force-free extrapolation of the photospheric magnetic field observed at MSFC with a resolution of 2″.34. The mean results are the following:

1. A very good agreement is found above the large leading sunspot of the group, assuming a potential extrapolation of the magnetic field and a constant conductive flux in the transition region ranging from 2 × 10⁶ to 10⁷ erg cm^?2s^?1.
2. A strong radio source, associated with a new-born moving sunspot, cannot be ascribed to thermal emission. It is suggested that this source may be due to synchrotron radiation by mildly relativistic electrons accelerated by resistive instabilities occurring in the evolving magnetic configuration. An order-of-magnitude computation of the expected number of accelerated particles seems to confirm this hypothesis.

  相似文献   

Analysis of the supergranulation structure in coronal holes     

G. Calamai  F. Chiuderi Drago  G. Pettini 《Solar physics》1980,65(1):167-170

Monochromatic rasters of six EUV lines taken in the centre of a coronal hole are analysed and the cell-network structure at different heights in the solar atmosphere is shown. Also a comparison with the average cell-centre and network intensities of another coronal hole is performed showing a good agreement between the two.  相似文献   

Weather routing in long-distance Mediterranean routes     

A. M. S. Delitala  S. Gallino  L. Villa  K. Lagouvardos  A. Drago 《Theoretical and Applied Climatology》2010,102(1-2):125-137

The selection of ship routes based on modern weather forecasting is a mean of computing optimum shipping routes thereby increasing safety and comfort at sea, cutting down on transit time, and reducing fuel consumption. Further empirical research in the effectiveness of modern weather routing applications is required especially in applications concerning shorter routes in enclosed seas of limited geographical extent such as the Mediterranean Sea. The present study used two climatological simulations to test this state-of-the-art approach to ship routing. Simulations represented two theoretical routes: (1) a route between Italy and Greece and (2) a route between Cyprus and Italy. Both routes were analyzed across varying simulated climatic conditions and the results were compared with those of control routes. Furthermore, results were analyzed in terms of passenger and crew comfort, bunker consumption by ships, and time of crossing. The first simulation showed that weather routing would improve ship performance on 37% of days while the second simulation revealed that weather routing would support ship captains virtually all the time.  相似文献   

The structure of coronal magnetic loops     

Claudio Chiuderi  Riccardo Giachetti  Gerard Van Hoven 《Solar physics》1977,54(1):107-122

We present here a model, based on observations, for the magnetic-field equilibrium of a cool coronal loop. The pressure structure, taken from the Harvard/Skylab EUV data, is used to modify the usual force-free-field form in quasi-cylindrical symmetry. The resulting field, which has the same direction but different strength, is calculated and its variation displayed. Finally, localized interchange stability is evaluated and discussed, as the first step in a subsequent complete magnetohydrodynamic-stability analysis.  相似文献   

Clam dredging effects and subsequent recovery of benthic communities at different depth ranges     

R. Constantino  M.B. Gaspar  J. Tata-Regala  S. Carvalho  J. Cúrdia  T. Drago  R. Taborda  C.C. Monteiro 《Marine environmental research》2009,67(2):89-99

This study aimed to assess the potential effects of clam dredging and the subsequent recovery of the benthic environment. Two experimental areas located at 6 and 18 m depth were established in order to analyse whether impacts and recovery of benthic environment are depth-related. Study areas were located within an area closed to dredging and two different plots were established at both depths. One of the plots was subjected to intense clam dredge-fishing, while the other was undisturbed and therefore used as control. Sampling followed a BACI design, with samples for macrobenthic, meiobenthic and sediment particle size analysis being taken by SCUBA divers from both areas before and after fishing stress. For both depths, impacts on the benthic environment were very low resulting in high recovery rates. Nevertheless, at shallower depths communities demonstrated a faster recovery. It was shown that depending on the faunal component used as a bioindicator, different results can be observed. Generally deposit-feeding organisms with scales or chitinous plates and vermiform shape (mainly crustaceans, polychaetes and ophiuroids), without external protection, were the most affected by dredging, while some polychaetes without external protection and with a carnivorous feeding mode seemed to be enhanced by fishing. The low level of perturbations induced by the dredging activities was comparable to the impact of surface waves on the bottom, as experiments were undertaken in wave-dominated environments. The coexistence of storm events during the study period proved to have similar or even more deleterious effects on the benthic environment. It appears that communities from hydrodynamic fishing grounds that are well adapted to natural physical stress are not highly affected by dredging.  相似文献   

EUV and radio spectrum of coronal holes     

Franca Chiuderi Drago 《Solar physics》1980,65(2):237-250

From the intensity of 19 EUV lines whose formation temperature {ovT} ranges from 3 × 10⁴ to 1.4 × 10⁶, two different models of the transition region and corona for the cell-centre and the network are derived. It is shown that both these models give radio brightness temperatures systematically higher than the observed ones. An agreement with radio data can be found only with lines formed at low temperature ({ovT} < 8.5 × 10⁵) by decreasing the coronal temperature and the emission measure. The possibility of resolving the discrepancy by using different ion abundances has been also investigated with negative results.  相似文献   

Winter dynamics on the northern Portuguese shelf. Part 2: bottom boundary layers and sediment dispersal     

J. Vitorino  A. Oliveira  J. M. Jouanneau  T. Drago 《Progress in Oceanography》2002,52(2-4)

The northern Portuguese shelf, between 41°N and 42°N, is characterised by the presence of a mid-shelf mud deposit, the Douro Mud Patch (DMP). Observations conducted between July 1996 and June 1999 under the framework of project OMEX II–II, are used to examine the impact of the dynamic processes in the lower water column, particularly on the DMP. The typical wave conditions observed during the winter maintain a highly energetic environment, capable of promoting the erosion of fine sediments at mid-shelf depths. However, the bottom nepheloid layers generated beneath these waves only extend a few meters above the bottom and are contained within rocky outcrops with similar heights that fringe the outer shelf. Each year there are about ten storms, mostly associated with southerly winds that create downwelling conditions over the shelf. The waves associated with these storms produce shear velocities over 3 cm/s at mid-shelf and bottom nepheloid layers which extend a few tens of meters above the bottom and spread offshore, over the outer shelf and upper slope. A rough estimate suggests that these events account for an offshore export of about 20×10⁶ kg of fine sediments each year (equivalent to 1–2% of sediments trapped at DMP).  相似文献   

Acoustic waves in the lower solar atmosphere     

C. Chiuderi  C. Giovanardi 《Solar physics》1975,41(1):35-42

The propagation and dissipation of acoustic waves in the lower solar atmosphere is studied. The level of shock formation is computed for various initial conditions. It is shown that shocks form rather low in the atmosphere and that this result does not depend critically on the assumed initial conditions.  相似文献