Abstract This study presents the characteristics of small-scale gravity waves in the mesosphere region as derived from the imaging riometer data at high altitude (~90 km) over SANAE (72˚S, 3˚W). Wavelet analysis and FFT (Fast Fourier transform) have been applied to extract short period gravity wave parameters for the year 2000. The horizontal wavelength, phase speed and observed period of gravity waves are typically 10-100 km, 5-60 m.s-1 and 3-60 minutes, respectively. The horizontal propagation direction is north-eastward throughout the year. This could probably be due to selective filtering by the zonal wind. Zonal and meridional winds in the region of the MLT (mesosphere and lower thermosphere) have been measured using HF radars at high latitudes in the southern hemisphere. Data from January 2000 to December 2003 have been used with the aim of investigating the characteristics of planetary wave activity at ~90 km. For SANAE and Halley stations, 2-, 5-, 10-, 16- and 20-day planetary waves are dominant in summer and winter. The results show the seasonal variations of the mean winds, which are caused by the internal variability of the quasi stationary planetary waves. Planetary wave coupling processes between UKMO assimilated and mesospheric data have also been investigated. The cross wavelet results show a strong coupling during winter months. The results suggest that planetary waves are generated at lower atmospheric heights and propagate upwards into mesospheric heights. However, not all observed disturbances in mesospheric heights can be explained by the propagation of planetary waves from lower atmospheric heights.

Deterministic and stochastic weighting methods are commonly used methods for estimating missing precipitation rain gauge data based on values recorded at neighboring gauges. However, these spatial interpolation methods seldom check for their ability to preserve site and regional statistics. Such statistics and primarily defined by spatial correlations and other site-to-site statistics in a region. Preservation of site and regional statistics represents a means of assessing the validity of missing precipitation estimates at a site. This study evaluates the efficacy of traditional interpolation methods for estimation of missing data in preserving site and regional statistics. New optimal spatial interpolation methods intended to preserve these statistics are also proposed and evaluated in this study. Rain gauge sites in the state of Kentucky are used as a case study, and several error and performance measures are used to evaluate the trade-offs in accuracy of estimation and preservation of site and regional statistics. / by Husayn El Sharif. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Trends in streamflow extremes at a regional scale linked to the possible influences of four major oceanic-atmospheric oscillations are analyzed in this study. Oscillations considered include: El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and North Atlantic Oscillation (NAO). The main emphasis is low flows in the South-Atlantic Gulf region of the United States. Several standard drought indices of low flow extremes during two different phases (warm/positive and cool/negative) of these oscillations are evaluated. Long-term streamflow data at 43 USGS sites in the region from the Hydro-Climatic Data Network that are least affected by anthropogenic influences are used for analysis. Results show that for ENSO, low flow indices were more likely to occur during La Niña phase; however, longer deficits were more likely during El Niño phase. Results also show that for PDO (AMO), all (most) low flow indices occur during the cool (warm) phase. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

Nuvens desempenham um papel fundamental no balanço radiativo terrestre, e o conhecimento de suas propriedades micro e macrofísicas é importante para o estudo do clima global. O desenvolvimento convectivo de nuvens está intimamente relacionado ao comportamento microfísico de seus hidrometeoros, os quais são influenciados pela variação nas concentrações de aerossóis disponíveis na atmosfera. Este trabalho utiliza o sensoriamento remoto por satélites para analisar a evolução diurna de propriedades ópticas de hidrometeoros de nuvens sobre a Amazônia. Para tanto, medidas de radiância efetuadas pelos canais 1, 2 e 4 do satélite geoestacionário GOES 13 para os anos de 2012, 2013, 2014 e 2015 foram aliadas a códigos computacionais de transferência radiativa visando a obtenção de estimativas de raios efetivos de gotas e partículas de gelo em nuvens convectivas. A variação temporal de parâmetros microfísicos ao longo do dia foi analisada durante as estações seca e úmida em dois locais prístinos e outros dois locais significativamente atingidos pela fumaça de queimadas na Amazônia. A profundidade óptica de aerossóis ( a em 550 nm) variou de 0,1 a 0,2 na maior parte do ano (estação úmida) sobre todos os locais. Na estação seca nos sítios prístinos observou-se um a em torno de 0,5 unidades, e de cerca de 0,8 nos sítios degradados. Os resultados mostram que para todos os locais analisados há 32% mais pixels de nuvens durante a estação úmida do que na seca. As distribuições relativas de refletâncias em 0,63 m e da temperatura de brilho em 11 m indicam que em todos os sítios e épocas do ano há predominância de nuvens menos espessas e mais quentes sobre a Amazônia. A análise da refletância em 3,90 m indicou que nos quatro locais ocorre uma redução do raio efetivo de hidrometeoros de nuvens quentes na estação seca em relação à estação úmida. A distribuição de raios efetivos é bimodal para todos os sítios e estações analisados, sendo a variação diurna dessa distribuição consistente com processos de desenvolvimento vertical de nuvens e crescimento de hidrometeoros. Esse mecanismo ocorre de maneira distinta em locais mais e menos poluídos, sendo que para regiões mais poluídas e desmatadas o desenvolvimento vertical de tamanhos de partículas na época seca se dá de maneira mais lenta do que na úmida. Para as áreas mais atingidas pela pluma de fumaça durante a estação seca os raios efetivos de gotas/cristais de gelo com temperatura de brilho maior que -20°C praticamente não mudam, sofrendo uma variação máxima de 2 m num período de 2 horas. Para o mesmo intervalo de temperaturas e de tempo a estação seca em ambientes mais limpos apresenta uma variação de até 6 m nos raios efetivos das partículas. Esse resultado é parcialmente compatível com modelos conceituais que procuram explicar efeitos microfísicos de aerossóis sobre o tamanho de hidrometeoros em nuvens. O atraso no crescimento vertical de hidrometeoros é mais pronunciado perto do meio dia solar e em locais onde as concentrações de aerossóis provenientes de queimadas são maiores. / Clouds play a key role in Earths radiative balance. The knowledge of its micro and macrophysical properties is important for the study of global climate. The life cycle of convective clouds is closely related to the microphysics of its hydrometeors, which are influenced by many factors including variations in the concentration of atmospheric aerosols. This study uses remote sensing by a satellite to analyze the diurnal evolution of reflective properties of clouds over Amazon. Radiance measurements performed by channels 1, 2 and 4 of the imager instrument onboard GOES-13 geostationary satellite, from 2012 to 2015, were analyzed using radiative transfer and computational codes. This allowed deriving estimates of the effective radius of cloud droplets and ice particles in convective clouds. The temporal variation of microphysical parameters throughout the day was analyzed during the dry and wet seasons at two pristine sites and two other sites significantly affected by biomass burning smoke in the Amazon. The aerosol optical depth ( a at 550 nm) ranged from 0.1 to 0.2 for most of the year (wet season) over all sites. In the dry season at the pristine sites a a of about 0.5 units was observed, while about 0.8 units were measured at the degraded sites. The results show that for all analyzed sites there were 32% more cloudy pixels during the wet season than in the dry season. The relative distribution of reflectance at 0.63 m and the brightness temperature at 11 m indicate that at all sites and times of the year there is a predominance of shallow warm clouds in the Amazon. The analysis of the reflectance at 3.90 m indicated that at the four sites a reduction of the effective radius of hydrometeors in warm clouds occurs in the dry season in comparison to the wet season. The distribution of effective radius is bimodal for all sites and seasons. The diurnal variation of this bimodal distribution is consistent with processes of vertical cloud development and hydrometeor growth. This mechanism occurs differently in the pristine and degraded sites. At polluted and deforested regions the vertical development of particle sizes in the dry season occurs more slowly than in pristine ones. For the areas more affected by smoke plumes during the dry season the effective radius of drops/ice crystals of clouds with brightness temperature greater than -20°C show small changes with height, undergoing a maximum variation of 2 m in 2 hours. For the same temperature range and time interval in the dry season, clouds in cleaner environments showed a variation up to 6 m in the effective radius of particles. This result is partly compatible with conceptual models that seek to explain microphysical effects of aerosols on the size of hydrometeors. The vertical growth delay of hydrometeors is more pronounced near local solar noon and in places where the concentration of smoke aerosols is higher.

This thesis details the application of a medium frequency (MF) Doppler radar to observations of meteoroids entering the Earth's atmosphere. MF radars make possible a greater height coverage of the meteor region (70 to 160 km) than conventional meteor radars. However this type of radar has generally been under-utilised for meteor observations, primarily due to the less than ideal radio environment associated with MF systems. This situation demanded selection of the most appropriate radar meteor techniques and in this respect a variety of techniques are evaluated for application at this frequency. The 2 MHz radar system used in this study is located at the Buckland Park research facility (35.6 deg. S, 138.5 deg. E), near Adelaide, South Australia and is operated by the Department of Physics of the University of Adelaide. This radar has the largest antenna of any MF radar with 89 crossed dipoles distributed over an area of about 1 km in diameter. Beam forming is achieved by varying the phase to groups of elements of the array. The array was constructed in the 1960's, and while having several upgrades, a preliminary examination of the array and associated systems indicated that a significant amount of maintenance work would be required to enable the system to be used for meteor observations. It was also apparent that the software used with the radar hardware for atmospheric studies was not suitable for processing meteor data. Thus a major refurbishment of the radar hardware, as well as the development of appropriate software, was initiated. The complete radar system was divided into its constituent components of antenna array, transmitter, receiver and computer systems. The transmitter and receiver systems were examined and various improvements made including increasing total output power and enhancing beam steering capability. Time domain reflectometry (TDR) techniques were extensively used on the antenna array, as many feed cables showed the presence of moisture. New hardware in the form of a portable power combining system was designed, constructed and tested to further increase radar experimental capabilities. Techniques were developed that verified system performance was to specification. Extensive night time observations of sporadic and shower meteor events were made over a two and a half year period. A particular study was made of the Orionids shower as well as other meteor activity on the night of 22 October 2000. Using the upgraded beam swinging features of the array, a narrow radar beam was used to track the shower radiant in an orthogonal sense so as to maximise the number of shower meteors detected. From each echo, various intrinsic meteoroid parameters were determined, including meteor reflection point angle-of-arrival using a five-element interferometer, echo duration and height; meteoroid speeds were determined using the Fresnel phase time technique. Meteor echoes belonging to the Orionids radiant were selected using a coordinate transform technique. The speed was then used as an additional discriminant to confirm the Orionid shower members. A second radiant, observed at a slightly higher declination is classified as also part of the Orionid stream. The sporadic meteor component in the data set was examined and found to exhibit speeds much higher than expected for sporadic meteors at the time of the observations. However, these results are consistent with a selection bias based on meteoroid speed, that is inherent in radar observations. The Orionid observations indicate that the refurbishment of the radar system and the introduction of new software for meteor analysis has been successfully achieved and that radar meteor studies can now be carried out routinely with the Buckland Park 2 MHz radar. Moreover it has been shown for the first time that meteoroid speeds can be determined with a MF radar operating on a PRF as low as 60 Hz. / Thesis (Ph.D.)--School of Chemistry and Physics, 2003.

A 50 MHz Frequency Modulated Continuous Wave (FMCW) radar system, developed at the University of Saskatchewan to provide improved spatial and temporal resolution measurements of auroral E-region plasma processes, introduces ambiguous spectral information, due to spectral ghosting, for scattering events in which multiple radar echoes are detected. This thesis identifies two Linearly Frequency Modulated (LFM) radar waveforms used by the FMCW system as the source of the ghosting. An analysis procedure designed to counteract the spectral ghosting problem is developed but is not an ideal solution, and therefore replacement of the LFM waveforms is recommended.<p> A detailed investigation of alternative radar waveforms using the Ambiguity Function and Ambiguity Diagram techniques is performed. A frequency coded continuous wave radar waveform based on a composite Costas sequence is proposed as a successor to the LFM waveforms. The composite Costas radar waveform will conserve the spatial and temporal resolutions extended by the LFM waveforms and preclude any spectral ghosting. Implementing the proposed radar waveform and avoiding receiver saturation issues with the mono-static FMCW radar system in which both the transmitting and receiving antenna arrays are simultaneously and continuously active and geographically co-located is also discussed.<p> In addition to this, two 50 MHz backscatter events are presented in this thesis to demonstrate the effectiveness of the FMCW system, notwithstanding the spectral ghosting complication. The first event from November 21, 2009 is identified as a Type 1 instability and the second from September 13, 2009 is identified as a Type 2 instability which lasted for ~ 16 minutes. Linear plasma fluid theory is used to provide a brief interpretation of both scattering events.

A 50 MHz Frequency Modulated Continuous Wave (FMCW) radar system, developed at the University of Saskatchewan to provide improved spatial and temporal resolution measurements of auroral E-region plasma processes, introduces ambiguous spectral information, due to spectral ghosting, for scattering events in which multiple radar echoes are detected. This thesis identifies two Linearly Frequency Modulated (LFM) radar waveforms used by the FMCW system as the source of the ghosting. An analysis procedure designed to counteract the spectral ghosting problem is developed but is not an ideal solution, and therefore replacement of the LFM waveforms is recommended.<p> A detailed investigation of alternative radar waveforms using the Ambiguity Function and Ambiguity Diagram techniques is performed. A frequency coded continuous wave radar waveform based on a composite Costas sequence is proposed as a successor to the LFM waveforms. The composite Costas radar waveform will conserve the spatial and temporal resolutions extended by the LFM waveforms and preclude any spectral ghosting. Implementing the proposed radar waveform and avoiding receiver saturation issues with the mono-static FMCW radar system in which both the transmitting and receiving antenna arrays are simultaneously and continuously active and geographically co-located is also discussed.<p> In addition to this, two 50 MHz backscatter events are presented in this thesis to demonstrate the effectiveness of the FMCW system, notwithstanding the spectral ghosting complication. The first event from November 21, 2009 is identified as a Type 1 instability and the second from September 13, 2009 is identified as a Type 2 instability which lasted for ~ 16 minutes. Linear plasma fluid theory is used to provide a brief interpretation of both scattering events.

This thesis details the application of a medium frequency (MF) Doppler radar to observations of meteoroids entering the Earth's atmosphere. MF radars make possible a greater height coverage of the meteor region (70 to 160 km) than conventional meteor radars. However this type of radar has generally been under-utilised for meteor observations, primarily due to the less than ideal radio environment associated with MF systems. This situation demanded selection of the most appropriate radar meteor techniques and in this respect a variety of techniques are evaluated for application at this frequency. The 2 MHz radar system used in this study is located at the Buckland Park research facility (35.6 deg. S, 138.5 deg. E), near Adelaide, South Australia and is operated by the Department of Physics of the University of Adelaide. This radar has the largest antenna of any MF radar with 89 crossed dipoles distributed over an area of about 1 km in diameter. Beam forming is achieved by varying the phase to groups of elements of the array. The array was constructed in the 1960's, and while having several upgrades, a preliminary examination of the array and associated systems indicated that a significant amount of maintenance work would be required to enable the system to be used for meteor observations. It was also apparent that the software used with the radar hardware for atmospheric studies was not suitable for processing meteor data. Thus a major refurbishment of the radar hardware, as well as the development of appropriate software, was initiated. The complete radar system was divided into its constituent components of antenna array, transmitter, receiver and computer systems. The transmitter and receiver systems were examined and various improvements made including increasing total output power and enhancing beam steering capability. Time domain reflectometry (TDR) techniques were extensively used on the antenna array, as many feed cables showed the presence of moisture. New hardware in the form of a portable power combining system was designed, constructed and tested to further increase radar experimental capabilities. Techniques were developed that verified system performance was to specification. Extensive night time observations of sporadic and shower meteor events were made over a two and a half year period. A particular study was made of the Orionids shower as well as other meteor activity on the night of 22 October 2000. Using the upgraded beam swinging features of the array, a narrow radar beam was used to track the shower radiant in an orthogonal sense so as to maximise the number of shower meteors detected. From each echo, various intrinsic meteoroid parameters were determined, including meteor reflection point angle-of-arrival using a five-element interferometer, echo duration and height; meteoroid speeds were determined using the Fresnel phase time technique. Meteor echoes belonging to the Orionids radiant were selected using a coordinate transform technique. The speed was then used as an additional discriminant to confirm the Orionid shower members. A second radiant, observed at a slightly higher declination is classified as also part of the Orionid stream. The sporadic meteor component in the data set was examined and found to exhibit speeds much higher than expected for sporadic meteors at the time of the observations. However, these results are consistent with a selection bias based on meteoroid speed, that is inherent in radar observations. The Orionid observations indicate that the refurbishment of the radar system and the introduction of new software for meteor analysis has been successfully achieved and that radar meteor studies can now be carried out routinely with the Buckland Park 2 MHz radar. Moreover it has been shown for the first time that meteoroid speeds can be determined with a MF radar operating on a PRF as low as 60 Hz. / Thesis (Ph.D.)--School of Chemistry and Physics, 2003.

This thesis details the application of a medium frequency (MF) Doppler radar to observations of meteoroids entering the Earth's atmosphere. MF radars make possible a greater height coverage of the meteor region (70 to 160 km) than conventional meteor radars. However this type of radar has generally been under-utilised for meteor observations, primarily due to the less than ideal radio environment associated with MF systems. This situation demanded selection of the most appropriate radar meteor techniques and in this respect a variety of techniques are evaluated for application at this frequency. The 2 MHz radar system used in this study is located at the Buckland Park research facility (35.6 deg. S, 138.5 deg. E), near Adelaide, South Australia and is operated by the Department of Physics of the University of Adelaide. This radar has the largest antenna of any MF radar with 89 crossed dipoles distributed over an area of about 1 km in diameter. Beam forming is achieved by varying the phase to groups of elements of the array. The array was constructed in the 1960's, and while having several upgrades, a preliminary examination of the array and associated systems indicated that a significant amount of maintenance work would be required to enable the system to be used for meteor observations. It was also apparent that the software used with the radar hardware for atmospheric studies was not suitable for processing meteor data. Thus a major refurbishment of the radar hardware, as well as the development of appropriate software, was initiated. The complete radar system was divided into its constituent components of antenna array, transmitter, receiver and computer systems. The transmitter and receiver systems were examined and various improvements made including increasing total output power and enhancing beam steering capability. Time domain reflectometry (TDR) techniques were extensively used on the antenna array, as many feed cables showed the presence of moisture. New hardware in the form of a portable power combining system was designed, constructed and tested to further increase radar experimental capabilities. Techniques were developed that verified system performance was to specification. Extensive night time observations of sporadic and shower meteor events were made over a two and a half year period. A particular study was made of the Orionids shower as well as other meteor activity on the night of 22 October 2000. Using the upgraded beam swinging features of the array, a narrow radar beam was used to track the shower radiant in an orthogonal sense so as to maximise the number of shower meteors detected. From each echo, various intrinsic meteoroid parameters were determined, including meteor reflection point angle-of-arrival using a five-element interferometer, echo duration and height; meteoroid speeds were determined using the Fresnel phase time technique. Meteor echoes belonging to the Orionids radiant were selected using a coordinate transform technique. The speed was then used as an additional discriminant to confirm the Orionid shower members. A second radiant, observed at a slightly higher declination is classified as also part of the Orionid stream. The sporadic meteor component in the data set was examined and found to exhibit speeds much higher than expected for sporadic meteors at the time of the observations. However, these results are consistent with a selection bias based on meteoroid speed, that is inherent in radar observations. The Orionid observations indicate that the refurbishment of the radar system and the introduction of new software for meteor analysis has been successfully achieved and that radar meteor studies can now be carried out routinely with the Buckland Park 2 MHz radar. Moreover it has been shown for the first time that meteoroid speeds can be determined with a MF radar operating on a PRF as low as 60 Hz. / Thesis (Ph.D.)--School of Chemistry and Physics, 2003.

Nuvens desempenham um papel fundamental no balanço radiativo terrestre, e o conhecimento de suas propriedades micro e macrofísicas é importante para o estudo do clima global. O desenvolvimento convectivo de nuvens está intimamente relacionado ao comportamento microfísico de seus hidrometeoros, os quais são influenciados pela variação nas concentrações de aerossóis disponíveis na atmosfera. Este trabalho utiliza o sensoriamento remoto por satélites para analisar a evolução diurna de propriedades ópticas de hidrometeoros de nuvens sobre a Amazônia. Para tanto, medidas de radiância efetuadas pelos canais 1, 2 e 4 do satélite geoestacionário GOES 13 para os anos de 2012, 2013, 2014 e 2015 foram aliadas a códigos computacionais de transferência radiativa visando a obtenção de estimativas de raios efetivos de gotas e partículas de gelo em nuvens convectivas. A variação temporal de parâmetros microfísicos ao longo do dia foi analisada durante as estações seca e úmida em dois locais prístinos e outros dois locais significativamente atingidos pela fumaça de queimadas na Amazônia. A profundidade óptica de aerossóis ( a em 550 nm) variou de 0,1 a 0,2 na maior parte do ano (estação úmida) sobre todos os locais. Na estação seca nos sítios prístinos observou-se um a em torno de 0,5 unidades, e de cerca de 0,8 nos sítios degradados. Os resultados mostram que para todos os locais analisados há 32% mais pixels de nuvens durante a estação úmida do que na seca. As distribuições relativas de refletâncias em 0,63 m e da temperatura de brilho em 11 m indicam que em todos os sítios e épocas do ano há predominância de nuvens menos espessas e mais quentes sobre a Amazônia. A análise da refletância em 3,90 m indicou que nos quatro locais ocorre uma redução do raio efetivo de hidrometeoros de nuvens quentes na estação seca em relação à estação úmida. A distribuição de raios efetivos é bimodal para todos os sítios e estações analisados, sendo a variação diurna dessa distribuição consistente com processos de desenvolvimento vertical de nuvens e crescimento de hidrometeoros. Esse mecanismo ocorre de maneira distinta em locais mais e menos poluídos, sendo que para regiões mais poluídas e desmatadas o desenvolvimento vertical de tamanhos de partículas na época seca se dá de maneira mais lenta do que na úmida. Para as áreas mais atingidas pela pluma de fumaça durante a estação seca os raios efetivos de gotas/cristais de gelo com temperatura de brilho maior que -20°C praticamente não mudam, sofrendo uma variação máxima de 2 m num período de 2 horas. Para o mesmo intervalo de temperaturas e de tempo a estação seca em ambientes mais limpos apresenta uma variação de até 6 m nos raios efetivos das partículas. Esse resultado é parcialmente compatível com modelos conceituais que procuram explicar efeitos microfísicos de aerossóis sobre o tamanho de hidrometeoros em nuvens. O atraso no crescimento vertical de hidrometeoros é mais pronunciado perto do meio dia solar e em locais onde as concentrações de aerossóis provenientes de queimadas são maiores. / Clouds play a key role in Earths radiative balance. The knowledge of its micro and macrophysical properties is important for the study of global climate. The life cycle of convective clouds is closely related to the microphysics of its hydrometeors, which are influenced by many factors including variations in the concentration of atmospheric aerosols. This study uses remote sensing by a satellite to analyze the diurnal evolution of reflective properties of clouds over Amazon. Radiance measurements performed by channels 1, 2 and 4 of the imager instrument onboard GOES-13 geostationary satellite, from 2012 to 2015, were analyzed using radiative transfer and computational codes. This allowed deriving estimates of the effective radius of cloud droplets and ice particles in convective clouds. The temporal variation of microphysical parameters throughout the day was analyzed during the dry and wet seasons at two pristine sites and two other sites significantly affected by biomass burning smoke in the Amazon. The aerosol optical depth ( a at 550 nm) ranged from 0.1 to 0.2 for most of the year (wet season) over all sites. In the dry season at the pristine sites a a of about 0.5 units was observed, while about 0.8 units were measured at the degraded sites. The results show that for all analyzed sites there were 32% more cloudy pixels during the wet season than in the dry season. The relative distribution of reflectance at 0.63 m and the brightness temperature at 11 m indicate that at all sites and times of the year there is a predominance of shallow warm clouds in the Amazon. The analysis of the reflectance at 3.90 m indicated that at the four sites a reduction of the effective radius of hydrometeors in warm clouds occurs in the dry season in comparison to the wet season. The distribution of effective radius is bimodal for all sites and seasons. The diurnal variation of this bimodal distribution is consistent with processes of vertical cloud development and hydrometeor growth. This mechanism occurs differently in the pristine and degraded sites. At polluted and deforested regions the vertical development of particle sizes in the dry season occurs more slowly than in pristine ones. For the areas more affected by smoke plumes during the dry season the effective radius of drops/ice crystals of clouds with brightness temperature greater than -20°C show small changes with height, undergoing a maximum variation of 2 m in 2 hours. For the same temperature range and time interval in the dry season, clouds in cleaner environments showed a variation up to 6 m in the effective radius of particles. This result is partly compatible with conceptual models that seek to explain microphysical effects of aerosols on the size of hydrometeors. The vertical growth delay of hydrometeors is more pronounced near local solar noon and in places where the concentration of smoke aerosols is higher.