COMPARISON AMONG TWO SIMPLE MODELS IN THE CLASSIFICATION OF DAYS AS RESPECT TO CLOUDINESS COMPARISON AMONG TWO SIMPLE MODELS IN THE CLASSIFICATION OF DAYS AS RESPECT TO CLOUDINESS Moura 1, R.G.; Correia 1, F. W. S.; Mendes 1, D. 1 CPTEC - INPE, Cachoeira Paulista-SP, Brasil ABSTRACT The Amazon Area, with its gigantic dimensions, a lot of times is studied by means of simulations using models. However, it is not easy, for example, to assess the amount of short wave radiation that reaches a certain surface, once this radiation depends mainly on the cloudiness cover, which is difficult to estimate. This work consists of verifying the performance of simple mathematic formulations to estimate the cloudiness, with the objective of evaluating the convenience of using those formulations in the classification of days as respect to cloudiness. The results showed that in both formulations used in this work, it was verified that a large percentage of days was classified as cloudy days, and most was classified as partially cloudy, reminding that these results refer to the rainy periods of the first LBA campaign. However the largest differences found among the formulations is in the classification of days of clear sky, as one of them classifies, like this, approximately half of the studied days. Possibly this is related with the different ranges established by each one of the different formulations. INTRODUCTION In accordance with the World-wide and routinely used Meteorological Organization for the meteorological observers, cloud is the visible set of very small ice or liquid water particles, or both at the same time, in suspension in the atmosphere. This set can also contain ice or liquid water particles in bigger dimensions, and originating particles, for example, of industrial vapors, smoke or dust. The main factors that intervene with the description of the aspect of a cloud are its dimensions, its form its structure and its texture. The process of cloud formation of convective, predominant origin in the Amazon region, initiates some hours after the sunrise and if it intensifies, following increase the daily one of the solar radiation, and its ending some hours before the one for of the sun. The cloudiness is defined as the sky fraction covered for clouds at the moment of the comment. However, in the Amazon region it is difficult to quantify this largeness, becoming necessary the use of adjusted mathematics models for this region (Moura, 2000). This work consists of verifying the performance of two simple mathematical formulations in the estimate of cloudiness, with the objective to evaluate the convenience of the use of such formulations in the classification of days how much the cloudiness for the Amazon region. USED DATA AND OBSERVED ASPECTS Had been used given gotten of period 26 of January the 11 of March of 1999, in environment of humid tropical forest, located in the Biological Reserve of Jaru (Rebio- Jaru-RO), (Lat.: 10° 05’ S; Long.: 61  56’ W). This small farm of forest process a Terra-firme vegetation with characteristics of and dense Bush, with average height of the canopy of approximately 35m with some emergent trees reaching 45m. METHODOLOGY In view of that the measures had been carried through during the rainy station of the region, the conditions of cloud covering had been presented sufficiently varied (also in the scale of one hour), with cloudy days, total partially cloudy and some days with sky characteristics clearly (clean), what it became sufficiently difficult the determination of conditions of characteristic days. Thus being, the collected data had been classified considering it percentage of cloud covering. For such, two simple methods of classification of days were used how much the cloudiness. The first method used in this classification was considered by Marques Filho (1997). According to this, it is considered time curve of observed maximum radiation, for the daylight, gotten from the observed absolute maximum values in each hour during all the period of the experiment, or either, of 26 of January the 11 of March of With this, the time curve of observed maximum radiation becomes thus, a referential to separate and to classify the days, being been overcome it reason enters the observed radiation in the top of the vegetal covering and the esteem maximum radiation for each instant. A similar method to the considered one for Marques Filho (1997), was used by Moura (2001) for the classification of days how much to the cloudiness. After the attainment of the daily curve of radiation of observed maximum short wave in the period, became related this curve with the curve incident radiation of gotten integrated short wave for each one of the 45 days of the experiment. With this, the days that had presented bigger value that 70 % of the integration of the radiation in the top of the tower, had been considered days of sky clearly; with a lesser value that 40 % cloudy days; e in the interval enters %, days partially darkened. The second used method to calculate the daily cloudiness was considered by Nkemdirim (1972). In this method, the reason enters and solar radiation measured next the surface and the calculated solar radiation in the top to the atmosphere (both integrated for the daylight) and divided in three percentile bands: 0.50 sky clearly. The solar radiation in the top of the atmosphere is calculated by the expression: Where D is in the distance Terra-Sol for one determined day, it is in the distance average Terra-Sol. it is the latitude of the place and is the declination of sun and h the hourly angle. Basically this study pyranometer used an instrument of the type (vide table 1), and from there, all the other referring information to the study had been function of the two applied methods. RESULTS AND DISCUSSION The figure (1), where the curves maximum possible and average for the period are shown. It was observed that the maximum value of measured radiation the 13 hours was of the order of 1250 Wm -2, while that the maximum value of radiation of the average curve was of the order of 667 Wm -2. As the figure (2), following the criterion adopted for the first method and knowing that the measures had been carried through during the rainy station of the region, more than confirmed that 68% of the studied days, had been classified as days partially darkened, about 19,5% cloudy days and only 12% days of sky clearly. Being that days 36, 43 and 44, they had been the days most representative of sky clearly of all the experiment, where the radiation in the surface was above of 75%. CONCLUSION Both the studied models had been capable to classify, practically the same number of days when the days if fit as partially cloudy. However, the biggest percentile difference was verified in the classified days as days of sky clearly, that it was of the order of 31.5% gotten by as the model, about 3 times bigger that the value gotten for the first model. This also happened again in the case of the classified days as days darkened for the first model, being that of this time, who was this overestimated about 4 times the number of days gotten for as the model. This behavior probably is related the different bands of classification imposed for each model. I recommend caution in the use of one or another possible method and always that followed of real information (visual) of cloudiness, for ends of validation of models. REFERENCES Marques Filho, A. O. Regime de radiação solar e características da vegetação – Modelos de inversão. Acta Amazônica, v. 27, n. 2, p , Moura, R. G. Estudo das Radiações Solar e Terrestre acima e dentro de uma Floresta Tropical Úmida. São José dos Campos. (INPE-XXXX- TDI/XXX) (Dissertação de Mestrado em Meteorologia) – Instituto Nacional de Pesquisas Espaciais, 2001, no prelo. Moura, R.G., Tota, J., Manzi, A. O., Gu, L. Medidas e Modelagem da Radiação Solar Interceptada pela Vegetação durante a Estação Chuvosa na Floresta da Rebio-jaru-Ro, Primeira Conferência Científica Internacional do LBA, Belém-PA, junho, Nkemdirim, L. C. A. A note on the albedo of surfaces. Journal of Applied Meteorology, v. 11, p , 1972.INSTRUMENTMEASUREMENTUNITMODELPyranometer Solar Radiation Wm -2 Radiometer CM11 (Kipp & Zonen, Delf, Holland) The figure (3) shows to the variation of the solar measure to surface and calculated radiation in the top of the atmosphere (integrated in the daylight) for the studied period. Certain daily variability in the measured radiation is observed, this must it the systems of mesoescala that they act in the region. The average was around 578 Wm -2, and the principle and 868 minims had been Wm -2 and 231 Wm -2, respectively the solar radiation in the top of the atmosphere presented little variation, with a average of 1325 Wm -2. The figure (4) presents the reason between the measured and calculated radiation. Also we verify certain daily variability caused by the systems that act in the region. The minor (17%) and greater (66%) value had been observed in days 52 and 36, respectively. The average of the period was of 44%, showing that for the period the sky partially was darkened (following the methodology of Nkemdirim, 1972). As well as shown in the previous model, as the model, also it classified the majority of the studied days as days partially darkened in about 63%, being 5% darkened and 31.5% for sky clearly. Figure - 1 Curves maximum possible and average for the period. Figure - 2 Percentage between the solar radiation measure and the estimate. Figure -3 Variation of the solar measure to surface and calculated radiation in the top of the atmosphere Figure - 4 Percentage between the solar radiation measure and the calculated one. Table - 1 General Specifications of the used instrument to make measured of solar radiation to the surface.