Vertical Wave Number Spectra of Ozone and Temperature Fluctuations in the Troposphere and Lower Stratosphere over Costa Rica (10  N, 83.4  W) a

Hyderabad, India Abstract: We examined the characteristics of ozone and temperature data over the tropical station Costa Rica during the period of 2012 – 2017, downloaded from Southern Hemisphere ADditional OZonsondes (SHADOZ) site. Our analysis reveals important variations of ozone and temperature structures in troposphere and stratosphere. An interannual variability of ozone fluctuations was observed in the measured wave activity and seasonal variation has also been observed with higher value in Summer Season (June July August). Vertical profiles of ozone and temperature have been used to examine the characteristics of wave number spectra of their fluctuations thereby assess the possible roles of gravity wave activity and to determine dominant vertical wavelengths of ozone spectra. Average slopes of wave number spectra are found to be –2.76 (–2.46) in the troposphere and –2.53 (–2.61) in the lower stratosphere for ozone (temperature) in summer. The corresponding values for winter are found to be –2.6 (–2.61) and –2.61 (–2.62) in the troposphere and stratosphere. Results indicate that there is consistency of the observed spectral slopes in the power law region which seems to be dominated by gravity wave activity. The energy density of ozone and temperature seems to be more in stratosphere when compared with troposphere. Mean vertical wave number spectra reveal dominant vertical wavelength 3.3 km in both troposphere The weekly profiles of ozone and temperature from SHADOZ over Costa Rica were used to produce meaningful vertical wave number spectra. The fluctuations have been obtained by removing quadratic fit from the profiles and the corresponding height profiles have been subjected to 5 km high pass filter. Then a Power Spectral Density analyses were carried out to form their respective wave number spectra. We examined the character of each spectra observed during 2012 – 2017. These individual spectra are averaged monthly to increase confidence level in the spectral power. In order to exclude the effect of the tropopause and Brunt Väisalä frequency squared on vertical wavenumber spectra, we first examined the tropopause height and it was found to be at ~17 km. Then the region between 15 and 18 km was taken as transition region between purely tropospheric behaviour below 15 km and purely stratospheric behaviour above 18 km. Now the complete altitude region has been divided into two regions Troposphere (5 – 15 km) and stratosphere (18 – 28 km). Table 2 shows the monthly and yearly mean spectral slopes of ozone and temperature in the wave number range of 4.69  10 –4 – 2.50  10 –3 cycle/m separately in troposphere (5 – 15 km) and stratosphere range (18 – 28 km). A considerable variability in the spectral slope of individual monthly ozone and temperature spectra was observed, which is consistent with the predictions of various gravity wave saturation models. Such variability in both slopes is also observed by other workers using Lidar and rocket measurements ([7], [8], [21]). This variability may be attributed to several factors that include intermittent sources in time and propagation through and interaction with a complex environment [9]. Reference [21] reported clear variation of monthly spectral slopes of ozone spectra with steepest slope of –4.10 and the of spectral averages i.e., 95 % confidence limit for normal distribution. Our results show that the spectral slopes are in general close to the slope of –3 predicted by various gravity wave models ([28], [29], [30]). References ([31], [32]) reported clear seasonal variation of the spectra in the lower stratosphere from radiosonde observations over a mid – latitude and observed spectra had slope closer to the model in winter while the summer spectra had small amplitudes and less spectral slopes (~ –2.5). A clear enhancement was observed in ozone spectra from troposphere to stratosphere in both the seasons, more prominent This paper presents spectral analysis of ozone and temperature in troposphere and stratosphere over tropical station Costa Rica during the period 2012 – 2017. We assessed the possible role of gravity waves by characterizing and determining the vertical wavelengths from the wave number spectra of ozone and temperature fluctuations. The profiles of both ozone and temperature reveal similar characteristics of their vertical structure as presented by [14]. The ozone tropopause and cold point tropopause of mean ozone (temperature) profiles 16.9 km (17.4 km) for winter season and 15.1 km (16.6 km) for summer season. A clear annual variation in ozone and temperature fluctuations are observed in stratosphere, but a mixture of annual and semiannual variation was found in troposphere. A clear seasonal variation is observed with maxima in summer months at all heights. Spectral properties of ozone and temperature fluctuations were characterized by forming their wave number spectra. The monthly spectral slopes of ozone and temperature spectra show considerable variability. But the mean values of spectral indices are found to be close to saturation model in both winter and summer seasons. The mean spectral slope of ozone spectra in troposphere is more than in stratosphere. Although various saturation models have been widely applied to predict the vertical wavenumber spectra of the wind, temperature and density fluctuations, in slope and amplitude, the theoretical predictions for the ozone spectrum are rudiment. Therefore, further theoretical studies are required in order to be able to explain well the observed ozone spectral slopes and amplitudes. The mean spectra show a dominant wavelength of 3.3 km in both troposphere and stratosphere. Indeed, the results presented in the paper appear to be the first comparative study of vertical wavenumber spectra of ozone and temperature fluctuations over tropical station. The project conducting and ozonesonde launches data authors