S. Morelli

An upgraded version of the Eta model

Upgrades implemented over a number of years in an open source version of the Eta model, posted at the CPTEC web site http://etamodel.cptec.inpe.br/, are summarized and examples of benefits are shown. The version originates from the NCEP’s Workstation Eta code posted on the NCEP web site http://www.emc.ncep.noaa.gov/mmb/wrkstn_eta, which differs from the NCEP’s latest operational Eta by having the WRF-NMM nonhydrostatic option included. Most of the upgrades made resulted from attention paid to less than satisfactory performance noted in several Eta results, and identification of the reasons for the problem. Others came from simple expectation that including a feature that is physically justified but is missing in the code should help. The most notable of the upgrades are the introduction of the so-called sloping steps, or discretized shaved cells topography; piecewise-linear finite-volume vertical advection of dynamic variables; vapor and hydrometeor loading in the hydrostatic equation, and changes aimed at refining the convection schemes available in the Eta. Several other modifications have to do with the calculation of exchange coefficients, conservation in the vertical diffusion, and diagnostic calculation of 10-m winds. Several examples showing improved performance resulting from the dynamics changes are given. One includes a case of unrealistically low temperatures in several mountain basins generated by a centered vertical advection difference scheme’s unphysical advection from below ground, removed by its replacement with a finite-volume scheme. Another is that of increased katabatic winds in the Terra Nova Bay Antarctica region. Successful forecast of the severe downslope zonda wind case in the lee of the highest peaks of the Andes is also shown, and some of the recent successful verification results of the use of the upgraded model are pointed out. The code is used at numerous places, and along with setup information it is available for outside users at the CPTEC Eta web site given above.

Trapping levels in anthracene crystals by thermally stimulated currents

SummaryThermally stimulated current (T.S.C.) measurements in anthracene crystals indicate the presence of various trapping levels. By regulating the excitation time and the excitation temperature we could isolate a monomolecular T.S.C. signal withE = (0.53 ± 0.03) eV and ϕ = 0.6.108 s-1 and determine the sign of the trapped carriers. The results obtained support the hypothesis that a level is involved which is strictly connected with the crystal lattice and presumably associated with chemical impurities contained in the crystal.RiassuntoMisure di correnti termicamente stimolate (T.S.C.) in cristalli di antracene hanno permesso di accertare la presenza di vari livelli di intrappolamento. Regolando tempo e temperatura di irraggiamento è stato possibile isolare un segnale di T.S.C. monomolecolare conE = (0.53 ± 0.03) eV e ϕ = 0.6 . 108 s-1. È stato inoltre accertato il segno dei portatori intrappolati. I risultati ottenuti avvalorano l’ipotesi che si tratti di un livello strettamente connesso con il reticolo cristallino, presumibilmente associate ad impurezze chimichc contenute nell’interno del cristallo.РезюмеИзмерения термическ и стимулированного т ока в кристаллах антрацена указывает на присутствие разли чных уровней ловушек. Регулируя время возбуждения и темпер атуру возбуждения, мы можем изолировать си гнал мономолекулярного т ермически стимулиро ванного тока сЕ= (0.53 ± 0.03) эВ и ϕ=0.6·108 сек-1 и кроме то го определить знак за хваченных носителей. Полученны е результаты подтвер ждают гипотезу, что им еется один уровень, тесно связанный с кри сталлической решетк ой и, вероятно, с химиче скими примесями, содержащимися внутр и кристалла.

Statistical forecasting of daily temperatures using short records of previous temperatures

Abstract From previous analysis of the daily minimum, mean and maximum temperatures in Modena, Italy over more than 100 years, it has already been demonstrated that each time series may be well represented by the sum of a seasonal deterministic function and a stationary gaussian stochastic signal. The latter was found to be autocorrelated and well represented by an autoregressive, moving-average process of order 2 and 1 respectively; AR(2)-MA(l). In this paper, starting from subrecords of daily temperatures taken from the whole record available in Modena, long-term and short-term predictions have been compared with the actually measured values. The positive results obtained by using the previous model suggest that such statistical forecasting can be performed also in other locations of similar climatic behavior, even if only short records of daily temperatures are available.

Quantitative estimation of climatic changes in the daily temperatures

Abstract In geophysical time series, such as daily temperatures, trends may be present due to global or to anthropogenic climatic changes. In this paper the quantitative estimation of the trend and of its statistical uncertainty is obtained by means of a fitting procedure, provided the stochastic behaviour of the time series has been previously determined, and the time random part of the time series is stationary. Moreover a detailed discussion on the reliability of the results is presented. The method has been tested with positive results on the minimum daily temperatures measured in bodena, Italy, since 1869.

LG-Mod: A Modified Local Gradient (LG) Method to Retrieve SAR Sea Surface Wind Directions in Marine Coastal Areas

This paper describes a novel SAR wind direction estimation method based on the computation of local gradients over quasi-linear and quasi-periodic structures detected by SAR imagery. The method relies upon the standard LG method for the part relevant to the computation of the local gradients. The novelty is that the dominant local wind direction and related accuracy are estimated using results derived from the Directional Statistics. The LG-Mod is validated against in situ coastal wind measurements provided by instrumented buoys with 63 ENVISAT ASAR images. Results show an overall agreement with RMSE values obtained for off-shore areas, but residual effects due to the complex phenomena occurring in the proximity of shoreline may degrade the performance when running in automated mode.

Eta Model Simulations and AMSR Images to Study an Event of Polynya at Terra Nova Bay, Antarctica

In the Terra Nova Bay (TNB) region, near-surface winds are persistently strong, in particular during the winter season and blow offshore with a high degree of directional constancy. This region is also known as a preferential zone of coastal polynyas. Polynyas are recurring areas of open water/thin ice surrounded by an ice-covered sea. Coastal polynyas form along ice-bound coasts; they are believed to be due to strong and persistent offshore winds and/or ocean currents which drive the sea ice away. As the ice is removed from the region of origin, open water is exposed and refrozen and the new ice is pushed away, so that coastal polynyas provide a source of new ice production. As the ice forms, much of the salt content in the freezing water is rejected, forming dense salty water, which tends to sink, eventually contributing to the deep ocean circulation. The horizontal surface temperature differences among the land ice, water, and sea ice are strong because the open water is close to the freezing point (−1.8°C for typical salt water). The energy exchange between the ocean and the atmosphere in the Antarctic marginal sea-ice zone is strongly influenced by the extent of sea-ice cover. While the sea ice acts as insulation, a direct contact between water and air is established in areas of open water, and intense energy exchanges occur due to the large difference of temperature between the water and the air above it. As a result, the polynya areas have an important impact on polar meteorology/climate.

Synergic use of SAR imagery and high-resolution atmospheric model to estimate wind vector over the Mediterranean Sea

An experiment whose aim is the retrieval of surface wind fields from SAR imagery coupled to a high resolution mesoscale numerical atmospheric model in semi-enclosed sea basin, is presented. A sea region belonging to North-Western Mediterranean Sea, which spans in W-E direction from Corsica (8.8 E) to Italian coast (10.5 E) and in N-S direction from Lygurian Sea (44.0 N) to North Tyrrhenian Sea (42.2 N), was selected as test area. Two consecutive ERS-2 SAR frames from the pass of March 30, 2000, along with a set of NOAA/AVHRR and MODIS images acquired on the same day were used for the analysis. SAR wind speeds and directions at 10 m above the sea surface were retrieved from predictions of the semi-empirical backscatter models CMOD4 and CMOD-IFREMER, which describe the dependency of the normalized radar cross section (NRCS) on wind vector and ERS-2 SAR image geometry. Surface wind vectors predicted by the meteorological ETA model were exploited as guess input to SAR wind inversion procedure to describe atmospheric conditions in the area, according a Bayesian approach recently proposed in literature. ETA is a three-dimensional, primitive equation, grid-point operational model running at the National Centers for Environmental Prediction of the U.S. National Weather Service. The model was adapted to run on selected regions of the Mediterranean basin with a nested very high, up to about 4.0 Km, resolution. The latter feature makes ETA model particularly suitble for its use in combination with SAR images. Besides, to simulate and predict several specific atmospheric weather phenomena, ETA outputs also include the vertical distributions of physical parameters such as air pressure, temperature, moisture up to about 25 Km. Apart some discrepancies in sparse and small areas, an overall agreement between SAR inversion results and ETA predictions was found. More importantly, it was found that the inversion methodology was not able to resolve wind speed modulations due to the manifestation of an atmospheric gravity wave, which occurred in the analyzed area as a result of the terrain disturbance to the air flow imposed by the peninsula located North of Corsica. Temporal evolution of the wave propagation phenomenon was allowed by inspection of NOAA/AVHRR and MODIS images through the detection of a cloud band associated to the atmospheric wave. A wave propagation model describing waves in the atmosphere owing to the disturbing action on the primary air flux by terrain features was thus used to account for the observed surface wind speed modulation on SAR image. Synergy with ETA model outputs was further exploited as atmospheric parameters up-wind the atmospheric wave were considered as input to the wave propagation model.

Direct and total irradiance: Measurement, calculation and comparison with Lowtran 6 and Lowtran 7 predictions

SummaryThe Lowtran code is used to determine solar transmission, direct solar irradiance and total radiance. In this paper results of comparisons between Lowtran 6 and Lowtran 7, the second including multiple scattering, are presented. These simulations are also compared with measurements of global irradiance carried out with a radiometer UV, in the range (295÷385) nm.

Quantitative analysis of Bora events in the Adriatic Sea by means of SAR-based techniques and the ETA model

Bora is the north-eastern wind which, blowing in the Adriatic Sea from NE and interacting with the orography of the Croatian Dinaric Alps, is characterized by multiple surface intense wind jets [1]. The exceptional Bora events of the beginning of February 2012 over the Gulf of Trieste have been studied by means of two ASAR Wide Swath (WS) images, acquired on the 2nd and 5th of February. Two different methods to extract wind direction from SAR images have been exploited to catch the spatial dynamic of this extreme phenomenon. In particular, SAR sea surface wind directions obtained with Local Gradient (LG) method [2] and the relatively novel technique based on the use of 2D continuous wavelet transform (CWT2) [3] have been analyzed. The retrieved wind directions extracted by the above mentioned methods have been used to estimate the wind speeds with a classical inversion procedure applied to the forward semi-empirical backscatter model CMOD-5 [4]. Results will be compared with wind fields simulated by the atmospheric ETA model [5].

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

SummaryDuring 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.