Simultaneous MST radar and radiosonde measurements at Gadanki (13.5 N, 79.2 E) 2. Determination of various atmospheric turbulence parameters

Transcription

1 RADIO SCIENCE, VOL. 38, NO. 1, 1014, doi: /2000rs002528, 2003 Simultaneous MST radar and radiosonde measurements at Gadanki (13.5 N, 79.2 E) 2. Determination of various atmospheric turbulence parameters A. K. Ghosh, A. R. Jain, and V. Sivakumar National MST Radar Facility, Tirupati, India Received 17 July 2000; revised 15 October 2001; accepted 8 May 2002; published 15 February [1] A campaign of one month simultaneous MST radar and radiosonde observations has been carried out from a tropical station Gadanki (13.5 N, 79.2 E) in India during summer monsoon season (July August). The observed signal spectral width by radar, temperature and pressure by radiosonde are made use to estimate the various atmospheric turbulence parameters such as eddy dissipation rate (e), vertical eddy diffusivity (K h ), inner scale size (l 0 ) and buoyancy scale length (L B ) in troposphere and lower stratosphere between 4 20 km. Applicability of the correction to the observed spectral width due to beam, shear and transience broadening is examined for the present series of measurements using Indian MST radar. The correction due to shear broadening of spectral width is noticed to be significant. The height structure of turbulence parameters from these measurements shows some distinct features. These features are discussed in terms of the observed background atmospheric parameters and magnitude of various turbulence parameters compared with those reported in literature and discussed in detail. INDEX TERMS: 3379 Meteorology and Atmospheric Dynamics: Turbulence; 6952 Radio Science: Radar atmospheric physics; KEYWORDS: MST radar, radiosonde, turbulence parameters, tropical easterly jet (TEJ), wind shear Citation: Ghosh, A. K., A. R. Jain, and V. Sivakumar, Simultaneous MST radar and radiosonde measurements at Gadanki (13.5 N, 79.2 E), 2, Determination of various atmospheric turbulence parameters, Radio Sci., 38(1), 1014, doi: /2000rs002528, Introduction [2] Turbulence present in different region of the atmosphere constitutes an important component of the atmospheric dynamics. The study of the turbulence is significant for understanding of general circulation as it contributes to dissipation of kinetic energy and enhances mixing of properties of the flow such as momentum. The presence of turbulence in the atmosphere also determines the mixing and diffusion of various minor constituents such as ozone. The various parameters such as eddy dissipation rate (e), eddy diffusivity (K h ), inner scale size (l 0 ) and buoyancy scale size (L B ) are some of the atmospheric turbulence parameters that defines characteristics of the turbulence in the atmosphere. These parameters are of considerable interest to radar and aircraft engineers for the selection of radar wavelength Copyright 2003 by the American Geophysical Union /03/2000RS and design of aircraft. These parameters are also of interest to meteorologist for understanding the atmospheric mixing and dynamics. The turbulence in the atmosphere is known to be caused either due to presence of strong vertical shears in horizontal winds or due to instability associated to the atmospheric convection, that occur frequently in tropical region. The former (later) generation of turbulence is called mechanical (thermal) turbulence. It should be mentioned here that in Indian tropical region strong vertical shears are observed during summer monsoon season (June September) that are associated to tropical easterly jet (TEJ) which occurs at the height of about km. These shears could significantly contribute to presence of mechanical turbulence at these height levels. [3] Direct measurements of large-scale turbulence were carried out using rocket experiments [Teitelbaum and Blamont, 1977; Thrane et al., 1985; Lubken et al., 1987], balloon [Barat, 1975, 1982; Yamanaka et al., 1985; Dalaudier and Sidi, 1987] and aircraft [Lilly et al., 1974]. Many workers have used in situ experiments

2 14-2 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, 2 successfully for smaller scale inhomogeneities of middle atmospheric turbulence, generated possibly by gravity wave breaking [Vinnichenko et al., 1973; Lilly et al., 1974; Barat, 1975, 1982; Yamanaka et al., 1985; Cot and Barat, 1986; Thrane et al., 1987; Lubken et al., 1987; Lubken, 1992]. All these results are based on small data sets, except a few climatological studies [Fukao et al., 1994; Nastrom and Eaton, 1997a, 1997b]. The validity of the different methods of measurements of the turbulence parameters is still controversial, as the assumptions underlying each method of measurement need thorough verification. More recently the ground based techniques such as VHF Doppler radar like ST (Stratosphere-Troposphere) and MST (Mesosphere-Stratosphere-Troposphere) radars have been used extensively for the determination of various turbulence parameters [Sato and Woodman, 1982; Gage and Balsley, 1984; Woodman and Rastogi, 1984; Sato et al., 1985; Hocking, 1985, 1986; Fukao et al., 1994; Jain et al., 1995; Nastrom and Eaton, 1997a, 1997b; Narayana Rao et al., 1997; Delage et al., 1997; Furumoto and Tsuda, 2001]. The radar techniques have the advantages that these can be used to make measurements of various turbulence parameters, almost on continuous basis with a high resolution in time and height. [4] There are two main methods by which MST radar can be utilized to measure the intensity of the turbulence in the atmosphere. The first method is power method. In this method the eddy dissipation rate e can be obtained by utilizing the radar measured received backscattered power [Gage et al., 1980; Sato et al., 1985; Hocking, 1985; Cohn, 1995; Narayana Rao et al., 1997; Delage et al., 1997; Ghosh et al., 2000; Furumoto and Tsuda, 2001]. For estimating meaningful values of e by this method, required that the radar received power be properly calibrated. It is also necessary to determine the fraction of the sample volume, which is filled by turbulence. Additional measurements of temperature and humidity are also required for this method to determining N 2 and M 2 [Cohn, 1995; Narayana Rao et al., 1997], where N and M represents Brunt Vaisala frequency and potential refractive index gradients respectively. The second method is known as spectral width method. This method makes use of radar received signal half spectral width to determine e [Cunnold, 1975; Sato and Woodman, 1982; Hocking, 1983, 1985; Fukao et al., 1994; Jain et al., 1995; Nastrom and Eaton, 1997a, 1997b; Narayana Rao et al., 1997]. This method is somewhat simpler than power method, the measurements of temperature and humidity are optional [Cohn, 1995; Narayana Rao et al., 1997]. The measured radar signal spectral width is directly related to the kinetic energy, which is associated to the turbulence. However, the measured signal spectral width may be contaminated by nonturbulent factors such as beam broadening and shear broadening [Atlas et al., 1969; Sato and Woodman, 1982; Hocking, 1983, 1985, 1986, 1996; Hocking and Lawry, 1989; Fukao et al., 1994; Jain et al., 1995; Narayana Rao et al., 1997; Nastrom, 1997]. It should be mentioned here that the determination of various turbulence parameters using the radar has a limitation. At some heights, even for the radar oblique beam of 10 or even larger, the echo arise due to refractivity structure associated to turbulence (more or less isotropic) and also partly due to refractivity structure associated to enhancement in N 2 [Hooper and Thomas, 1998; Hocking and Mu, 1997; Worthington et al., 1999; Jain et al., 2001]. This fact should be born in mind while interpreting the turbulence parameters determined using radar observations. [5] Most of the measurements of turbulence parameters are available for mid and high latitudes [Gage et al., 1980; Hocking, 1983, 1985; Nastrom et al., 1986; Fukao et al., 1994; Nastrom and Eaton, 1997a, 1997b], but only a few measurements are available for tropical latitudes [Sato and Woodman, 1982; Jain et al., 1995; Narayana Rao et al., 1997]. The turbulence parameters are known to depend on the background atmospheric conditions as well as on the latitude of the station and season. For Indian tropical region monsoon is one of the distinct phenomena accompanied by feature like TEJ. In the present series simultaneous MST radar and radiosonde measurements have been carried out from the radar site Gadanki (13.5 N, 79.2 E), a tropical station in India. These measurements have been carried out every day evening over a period of one month during summer monsoon season. These are the first set of simultaneous radar and radiosonde measurements from the radar site at Gadanki. The objective of this paper is to present height profiles of various atmospheric turbulence parameters like e, K h,l 0 and L B using the above measurements. The results brought out the height structure and characteristic features of turbulence parameters at this tropical station during summer monsoon season. These results are discussed in terms of the background atmospheric parameters. 2. Observations [6] National MST radar facility in India at Gadanki (13.5 N, 79.2 E) operating VHF pulse Doppler radar at a frequency of 53 MHz and peak power aperture product of Wm 2. The antenna consists of a array of 3 element Yagi aerials with a covering the geometric area of m 2. The radiation pattern of radar has 3 beam width with gain of 36 db and first side lobe level of 20 db [Jain et al., 1994; Rao et al., 1995]. The radar is operated every day in evening between 16:45 to 17:30 IST (11:15 to 12:00

3 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, UT), in a standard mode. Details of the experiment parameters and resolution of measurements are given in Table 1. Radiosonde have been launched everyday from 19 July to 14 August 1999 at 16:20 IST (about 10:50 UT). These measurements also include two sets of observation over diurnal cycle. Each of these diurnal cycle measurements includes observations at six hourly intervals. Radiosonde measurements of pressure, temperature and humidity data are obtained every one minute corresponding to a vertical height interval of 300 m. The radiosonde reached around 24 km in about 1 hour 20 min. from the time of launch. The radiosonde data are interpolated using linear interpolation at the height interval of 150 m to match the height levels of measurements by two instruments. The atmospheric stability parameter (N 2 ) and vertical shear of horizontal wind (@U h /@Z) are computed corresponding to each radar range gate. For these computations the vertical gradient are determined using three-point method. Thus, limiting the height resolution of these parameters to 300 m. 3. Methods of Determination of Turbulence Parameters 3.1. Energy Dissipation Rate (E) [7] Energy dissipation rate (e) at various height levels are an important characteristic of atmospheric turbulence and it represents the amount of turbulence energy converted into heat of the medium by viscous forces per unit mass per unit time. This particular parameter is important to meteorologists for understanding the energy dissipation and atmospheric dynamics. [8] The intensity of the turbulence also affects the root mean square velocity fluctuation of scatterers in the turbulence patch and this in turn produces changes in the spectral width of the backscattered signal received by the radar. It is therefore possible to use the spectral width of the signal to deduce the turbulence energy dissipation rate at the height of scatterer [see, e.g., Hocking, 1985]. The parameter e is related to mean square velocity fluctuations of the scatterers and the half power half spectral width of the received backscattered signal [Hocking, 1983, 1985; Fukao et al., 1994; Jain et al., 1995] by equation e ¼ 0:49V 2 N ¼ 0:33s 2 1=2 N ð1þ where s 1/2 the true half power half width of the received signal spectra. The parameter s 1/2 can be computed from the observed spectral width of the signal spectrum after duly correcting the same for beam, shear and transience broadening effects. The correction to the observed radar Table 1. Experimental Specification File (ESF) Used for the Present Study of Indian MST Radar Observation Parameter signal spectral width for various effects is discussed separately in section Vertical Eddy Diffusivity (K h ) [9] The vertical eddy diffusivity K h is defined by the momentum of heat and the vertical gradient of the mean potential temperature i.e. ¼ q0 w 0 ESF Pulse width (ms) 16 Interpulse period (ms) 1000 Coded/Uncoded Coded using 16 baud biphase supplementary Range resolution (m) 150 No. of beams 6 (E10y, W10y, Zy, Zx, N10x, S10x) a Coherent Integration 128 No. of FFT points 128 Nyquist frequency (Hz) ±4 (line of sight velocity v ±12 m/s) Doppler resolution (Hz) 0.06 (line of sight (rv) 0.18 m/s) Observational window: Lowest range bin (km) 3.6 Highest range bin (km) 32 Incoherent integration 1 Beam Dwell time (s) 16 STC length (ms) 40 No. of scan cycle 8 a E10y = beam direction 10 east from the zenith in east-west plane. W10y = beam direction 10 west from the zenith in east-west plane. Zy = Vertical beam direction formed using east-west plane array. Zx = vertical beam direction formed using north-south plane array. N10x = beam direction 10 north from the zenith in north-south plane. S10x = beam direction 10 south from the zenith in north-south plane. ð2þ where z is the altitude, w is the vertical velocity, q is potential temperature and the over bar and prime denote the mean field and the perturbations respectively. From the consideration energy budget of the turbulence and from the definition of the static stability parameter (N 2 )it can be shown [Fukao et al., 1994] that K h ¼ be N 2 ; where b ¼ R f ð3þ 1 R f where R f is the flux Richardson number. It should be noted that above expression gives a local value of K h for locally homogeneous turbulence (say for each radar volume cell). [10] Lilly et al. [1974] used a value 0.25 for R f and obtained b = 1/3 = This value of b is also consistent with the generalized formulation as given by Weinstock [1981] where the dominant turbulence scale is slightly

4 14-4 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, 2 smaller than the buoyancy scale. Equations (1), (2) and (3) yield K h 0:33eN 2 or K h 0:1s 2 1=2 N 1 ð4þ 3.3. Scale Size of Turbulence (l 0 and L B ) [11] The inner (l 0 ) and outer scale size (L B ) is important for the discussion of turbulence. At very small scale which are smaller than the inner scale of the turbulence (l 0 ) the kinetic energy density contained by the eddies is diminished due to viscous effects and turbulence energy is dissipated to heat. Therefore, at scale smaller than l 0, the turbulence cannot sustain itself. At very large scale called buoyancy or outer scale the buoyancy effects is important and turbulence eddies appear with the horizontal scale much larger than vertical dimension.the buoyancy scale size L B is given by Weinstock [1978]. Thus, parameter L B differentiates the radar backscatter from turbulence and statically stable regions and it is a transition scale between the inertial and buoyancy subrange turbulence [Hocking, 1985]. [12] The inner scale size of turbulence l 0 is estimated using the relationship 1 0 ¼ 7:4h ð5þ where h is the Kolmogroff microscale 1 4 h ¼ ð6þ and u ¼ u3 e 2: r ð7þ where u, e and r are the kinematic viscosity, eddy dissipation rate and the atmospheric density respectively. [13] For determining l 0, atmospheric density is taken from the local model [Sasi and Gupta, 1986; Sasi, 1994], which is representative of tropical region in India. [14] The buoyancy scale (L B ) determines the transient region between the inertial and buoyancy range is given by [Weinstock, 1978; Hocking, 1985; Jain et al., 1995] L B ¼ 2p 0:62 e1=2 N 3=2 ð8þ It should be mentioned here that equation (8) is applicable only to shear generated turbulence in statically stable atmosphere. For convective turbulence N 2 < 0 and above equation would therefore not be meaningful. 4. Correction for the Spectral Broadening Effects [15] The observed radar signal spectral width s 1/2 obs of consists of (i) the true spectral width s 1/2 arising due to backscatter from refractive index irregularities associated to atmospheric turbulence and partly due to (ii) beam broadening s 1/2 beam (iii) shear broadening s 1/2 shear and contamination due to transience s 1/2 trans as discussed by Fukao et al. [1994]. The observed spectral width (s 1/2 obs ) is to be corrected for various contaminations to obtained s 1/2 which is mainly due to turbulence i.e. 2¼ s1=2obs s1=2beam s1=2shear s1=2trans s 1=2 ð9þ [16] The beam broadening effect arises due to different radial velocities of the scatterers are observed in different parts of the finite beam width resulting in a broadening of the observed spectrum [Hocking, 1983, 1985, 1986, 1996; Fukao et al., 1994]. The contribution of this effect to the observed spectral width is given by s 1=2 beam d 1=2 ju h j; ð10þ where d 1/2 (0.019 rad for Indian MST radar) is the half power half width of the two way radar beam (1.1 ) and ju h j is the mean horizontal wind speed. [17] The shear broadening effect is observed basically due to changes in radial component of the wind over the sampled volume. This effect is an important one, when the beam is tilted from the vertical. This particular contribution can be written as s 1=2shear ¼ 1 Dz sin c ð11þ where j@u h /@zj is vertical shear of horizontal wind, Dz is range resolution and c is the beam zenith angle. In the present series of MST radar observations, Dz = 150 m and c =10. [18] The contamination due to transience of atmospheric motion arise due to change in wind during the beam dwell time which in turn depends on the total period of one observation i.e., beam dwell time is determined by the number of incoherent integration of the spectrum. In the present series of observations the number of incoherent integration used is unity and beam dwell time is 16 s. Therefore, contamination due to this effect to the observed spectral width, is expected to be minimum. [19] The procedure adopted for shear and beam-broadening correction to present series of data is discussed here. As evident from the equation (11) s 1/2 shear is proportional to the vertical shear of horizontal wind. Height profiles of the observed spectral width and wind shear are shown in Figure 1a for two days. From this figure effect of vertical shear on the observed signal spectral width (SW) can be noticed clearly. As the effect of shear broadening on SW is expected to be confined to a narrow height range where large vertical shears are present, correction for shear broadening is applied first to

5 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, Figure 1a. Height profiles of observed spectral width (s obs ) and the vertical shear in the horizontal wind for 21 and 27 July obtain the shear corrected spectral width (s 1/2sc ), which is given by following equation: 2¼ 2 2 s1=2obs s1=2shear ð12þ s 1=2sc [20] An examination of the equation (10) shows that the beam broadening correction is proportional to the horizontal wind speed suggesting that the observed spectral width should be large when U h is large and vice versa. It can be clearly noticed from the height profiles of spectral width (s obs ) and shear corrected full spectral width (s sc ) and U h, shown in Figure 1b for two days, that there is no significant increase in spectral width s obs as well as s sc at the height of observed enhanced horizontal winds (U h ). The observations show that spectral width (s obs or s sc ) does not show any enhancement due to increase in U h. This fact is evident from the observations for the other days also. Hence, it is implied that, for the present set of observations reported here, it is not necessary to apply the beam broadening correction. 5. Results 5.1. Height Profiles and Height-Date Contour Maps of Atmospheric Turbulence Parameters (E, K h,l 0,L B ) [21] The height profiles of N 2, Richardson number (Ri), loge, logk h,l 0 and L B for two days are given in Figures 2 and 3. The two height profiles of e in these figures are corresponding to (i) uncorrected spectral width; (ii) shear broadening corrected spectral width using equations (11). The height profiles of K h,l 0 and L B are obtained making use of e computed using shear corrected spectral width (s 1/2sc ) i.e. e c and using equations (4), (5) and (8) respectively. In the Figures 2 and 3 height profiles of various turbulence parameters are not drawn in the height range of km, as it is difficult to estimate the spectral width s 1/2obs accurately in this height range due to reduced detectability of the signal in this height interval. The height profile of e, e c and K h multiple peaks are observed on 21 July 1999 at the height between km i.e. at height of 16.8, and km (see Figure 2). Similarly, two peaks are observed in the height profile e, e c and K h on 27 July 99 between km i.e. at 17.5 and km (see Figure 3). Some of the peaks, such as at 16.8 km on 21 July 99 and at 17.5 km on 27 July 99 coincide to enhanced shear (see Figure 1a) and to small values of Ri (i.e. Ri < 1). This suggests that at these height levels, these peaks are prominently due to shear-generated turbulence as Ri is small. Other peaks coincide to enhancement in N 2. This suggests that these peaks are at least partly due to refractivity gradients due to enhanced N 2. The height profile of K h also shows similar peaks on both the days (see Figures 2 and 3).

6 14-6 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, 2 Figure 1b. Height profiles of observed spectral width (s obs ) shear corrected spectral width (s sc ) and the horizontal wind speed for 21 and 27 July Figure 2. Height profiles of the atmospheric stability parameter (N 2 ), Richardson number (Ri), energy dissipation rate (e), vertical eddy diffusivity (K h ), inner scale size (l 0 ) and buoyancy scale size (L B ) for 21 July In the third panel from left, two curves are given for e. The solid line curve refers to uncorrected spectral width and dotted curve refers to the shear corrected spectral width (see text). Shear corrected spectral width (s sc ) is used for computation of K h,l 0 and L B.

7 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, Figure 3. Same as Figure 2, but for 27 July [22] The inner scale length l 0 is 0.01 m at height of 4 km and 0.15 m at the 20 km. The buoyancy scale length L B in the upper troposphere (i.e., above 15 km) is noted to be much smaller as compared to its value at the lower heights. [23] Figure 4 shows the height profiles of loge c, logk h, l 0 and L B at six hourly interval from 28 July 99, 10:00 IST to 29 July 99, 17:00 IST. These observations are made use to examine the consistency of the measured height profiles of turbulence parameters over a day. It can be noticed that variance in turbulence parameters below 9 km and above 16 km is comparatively small and a peak in e c and K h, can be noticed clearly between17 18 km. The height-date-contour maps of loge c, logk h,l 0 and L B are shown in Figure 5. The secondary peak in e c and K h in the height range of km and a minimum in the height range of km are clearly evident from the contour maps of (Figure 5). Day-to-day variability in the height structure of these parameters can also be seen. The inner scale length l 0 is small at the lower heights. Larger values of l 0 are observed at higher heights. In contrast, values of L B are large at lower heights and noticed to decrease with height. Contour maps of l 0 and L B also show the day to day variability in height structure of these parameters. [24] Figure 6 shows that mean height profiles of loge c, logk h,l 0 and L B obtained using the data of all individual days during the campaign period i.e. 19th July to 14th August These profiles give an idea of height variation of these turbulence parameters at this tropical station during summer monsoon season. The horizontal bars show the standard deviation, representing day-today variability of these turbulence parameters. The mean height profiles of e c and K h, show a secondary peaks at the level between km. The height profile of l 0 show an increase with the height and L B shows that the values of this parameter at the heights above 15 km is much smaller than at lower heights in lower and middle troposphere. The scale length between l 0 and L B represent the inertial subrange of turbulence from 4 20 km Summary of Results [25] In the present study, simultaneous MST radar and radiosonde measurements from radar site are used to compute various atmospheric turbulence parameters and obtain the height profiles of e, K h,l 0 and L B for the tropical station Gadanki during the peak summer monsoon season. Most of the measurements of the turbulence parameters so far, are confined to the mid and high latitudes and only a few measurements are available for the equatorial and tropical latitudes. Therefore, the present series of measurements, which correspond to tropical station and for summer monsoon season, are very much relevant. [26] The determination of turbulence parameters from radar signal spectral width suffers from the complication that the observed radar signal spectral width need to be corrected for various external effects such as contribution due to beam, shear and transience broadening. These effects have been considered in details. Incoherent integration of the spectra is unity, in the present series of measurements. The contribution due to transience is therefore expected to be negligible. In the present series of observations, the effect of shear broadening is localized to heights where large shears are observed. Therefore, the shear correction is applied to obtain the shear broadening corrected spectral width. The present obser-

8 14-8 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, 2 Figure 4. The height profiles of energy dissipation rate (e), vertical eddy diffusivity (K h ), inner scale size (l 0 ) and buoyancy scale size (L B ) for 28 July 99 10:00 IST to 29 July 99 17:00 IST every 6 hours interval. vations also show that the shear corrected spectral width does not appear to depend on the magnitude of horizontal winds. This clearly suggests that, for present series of observations, there is no significant contribution due to beam broadening. It should be noted here that Indian MST radar at Gadanki has two-way half power half width equal to 1.1. [27] The turbulence parameters e, K h,l 0, and L B are computed keeping the above limitations in mind. Some of the salient features of the present series of observations are as follows: 1. The height profiles of turbulence parameters are representative of monsoon season for a tropical station. 2. The value of eddy dissipation rate at heights close to tropopause (i.e km) is about 10 4 m 2 s 3 which as high as the value of e observed at the height of 8 km. 3. The height profile of eddy diffusivity (K h ), also shows a small secondary peak at the altitude of about 17 km with a peak value of K h 0.05 m 2 s 1. At lower heights, i.e., 4 14 km, values of K h are in the range of m 2 s Height profiles of parameter L B for upper troposphere and lower stratosphere show low values whereas parameter l 0 show high values at these heights. This indicates that inertial subrange, in the upper troposphere and lower stratosphere is narrower as compared to the value at lower heights in troposphere. 6. Discussion [28] It would be interesting to compare height characteristics of various turbulence parameters and their magnitudes with the some of the available observations. Sato and Woodman [1982], from Arecibo radar (18 N) measurements, on one winter day, reported a value of e between 10 5 to 10 3 m 2 s 3 in the height range of km with a minimum value at the height of 17.4 km. The corresponding values for K h, reported by these

9 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, Figure 5. Date, height and intensity contour maps for e, K h,l 0 and L B using all the available data for the period of radiosonde campaign period. authors, are in range of 0.01 to 1.0 with a minimum value at 17.4 km. From the present set of measurements, corresponding values for the same height range, the value of e is in the range 10 5 to 10 3 and K h is in the range of 0.01 to 0.3. These values are of same order as reported by Sato and Woodman [1982]. Height characteristics of the turbulence parameters e and K h from present measurements are, however, different from those reported by Sato and Woodman [1982]. This is expected as Arecibo measurements correspond to winter month. The present series of measurements of e, K h and L B compares favorably with those reported by Sato et al. [1986] which are for the month of July, though for MU radar, a mid latitudes station. Jain et al. [1995] reported measurements of turbulence parameters for Gadanki, in the height range of 4 11 km using Indian MST radar in ST mode. These measurements refereed to one day in March. The magnitudes of e, K h and L B reported by Jain et al. [1995] compare well with the present measurements. [29] Fukao et al. [1994] presented three years of measurements of eddy diffusivity (K h ) using MU radar. Nastrom and Eaton [1997b] has presented climatology of K h at White Sand Missile Range (WSMR) during Nastrom and Eaton [1997a] also presented detailed climatology of e using WSMR for the period These measurements make use of the corrected signal spectral width and refer to mid latitudes. [30] The value of K h by Fukao et al. [1994] and Kurosaki et al. [1996] for the month of July is in the range of with a peak value at around 12 km. The corresponding value given by Nastrom and Eaton [1997b] is also in the same range but height structure of the profile in two cases is different. The present observations show that value of K h, above 14 km, is somewhat smaller ( m 2 s 1 ) as compared to those reported by Fukao et al. [1994] and Nastrom and Eaton [1997b]. The height structure of K h, from present measurement shows a secondary peak between km. This height structure of K h is similar to that reported by Nastrom and Eaton [1997b]. [31] The height profile of e as reported by Nastrom and Eaton [1997a] for the month of July for WSMR is very similar to present observations and comparable in magnitude. Both of these results show a secondary peak between km. A comparison of the present measurements of e with those reported by Narayana Rao et al. [1997] for Gadanki and for the month of July shows similarity in height structure but the magnitude from present observations appears to be significantly higher. [32] The height profiles of L B from present sets of measurements shows a value between m for the height range of 4 11 km. This compared well with the values of L B as reported by Jain et al. [1995] using

10 14-10 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, 2 Figure 6. Mean height profiles of e, K h,l 0 and L B, using the corrected spectral width of all the data for radiosonde campaign period. The horizontal bars show the standard deviation for the period of observation at each range gate. ST mode of Indian MST radar and by Sato et al. [1986] using MU radar. [33] To summarize, it can be mentioned that values of different turbulence parameters from present measurements are comparable to the earlier measurements from other studies. However, height structure of these parameters shows unique features, which can be considered typical of monsoon season for this tropical station. [34] Acknowledgments The National MST Radar Facility (NMRF) is set up jointly by the Council of Scientific and Industrial Research (CSIR), Defense Research and Development Organization (DRDO), Department of Electronics, Environment, Science and Technology and Space, Government of India with Department of Space as a nodal agency. The NMRF is operated by the Department of Space, Government of India, with partial support from CSIR. We wish to thank the staff of the National MST Radar Facility for the collection of data used in this paper. We would like to thank India Meteorological Department (IMD) for supporting the radiosonde observation campaign carried out from NMRF, Gadanki, during July August We would also like to thank the anonymous reviewers, whose suggestions have resulted in substantial improvement of the paper. References Atlas, D., R. C. Srevastava, and P. W. Sloss, Wind shear and reflectivity gradient effects on Doppler radar spectra, II, J. Appl. Meteorol., 8, , Barat, J., Etude experimentale de la structure du champ de turbulence dans la moyenne stratosphere, C. R. Acad. Sci., Ser. B, 280, , Barat, J., Some characteristics of clear air turbulence in the middle stratosphere, J. Atmos. Sci., 39, , Cohn, S. A., Radar measurements of turbulent eddy dissipation rate in the troposphere: A comparison of techniques, J. Atmos. Oceanic Technol., 12, 85 95, Cot, C., and J. Barat, Wave turbulence interaction in the stratosphere: A case study, J. Geophys. Res., 91, , Cunnold, D. M., Vertical transport coefficients in the mesosphere obtained from radar observations, J. Atmos. Sci., 32, , Dalaudier, F., and C. Sidi, Evidence and interpretation of a spectral gap in the turbulent atmospheric temperature spectra, J. Atmos. Sci., 44, , Delage, D., R. Roca, F. Bertin, J. Delcourt, A. Cremieu, M. Massebeuf, and R. Ney, A consistency check of three radar methods for monitoring eddy diffusion and energy dissipation rates through the tropopause, Radio Sci., 32, , Fukao, S., M. D. Yamanaka, N. Ao, W. K. Hocking, T. Sato, M. Yamamoto, T. Nakamura, T. Tsuda, and S. Kato, Seasonal variability of vertical eddy diffusivity in the middle atmosphere, 1, Three-year observations by the middle and upper atmosphere radar, J. Geophys. Res., 99, 18,973 18,987, Furumoto, J., and T. Tsuda, Characteristics of energy dissipation rate and effect of humidity on turbulence echo power revealed by MU radar RASS Measurements, J. Atmos. Sol. Terr. Phys., 63, , Gage, K. S., and B. B. Balsley, MST radar studies of wind and turbulence in the middle atmosphere, J. Atmos. Terr. Phys., 46, , Gage, K. S., J. L. Green, and T. E. Vanzandt, Use of Doppler radar for the measurement of atmospheric turbulence parameters from the intensity of clear air echoes, Radio Sci., 15, , 1980.

11 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, Ghosh, A. K., A. R. Jain, and V. Sivakumar, Characteristics of atmospheric wind, associated shear and turbulence: Indian MST radar measurement during summer monsoon season, Indian J. Radio Space Phys., 29, , Hocking, W. K., On the extraction of atmospheric turbulence parameters from radar backscatter Doppler spectra, 1, Theory, J. Atmos. Terr. Phys., 45, , Hocking, W. K., Measurements of turbulent energy dissipation rates in the middle atmosphere by radar techniques: A review, Radio Sci., 20, , Hocking, W. K., Observation and measurements of turbulence in the middle atmosphere with a VHF radar, J. Atmos. Terr. Phys., 48, , Hocking, W. K., An assessment of the capabilities and limitations of radars in measurements of upper atmospheric turbulence, Adv. Space Res., 17(11), 37 47, Hocking, W. K., and K. Lawry, Radar measurements of atmospheric turbulence intensities by both C n 2 and spectral width methods, in MAP Handbook, vol. 28, edited by C. H. Liu and B. Edwards, pp , Secr., Sci. Comm. on Sol.- Terr. Phys., Univ. of Ill., Urbana, Hocking, W. K., and P. K. L. Mu, Upper and middle tropospheric kinetic energy dissipation rate from measurements of C n 2 review of theories, in-situ investigations, and experimental studies using the Buckland Park atmospheric radar in Australia, J. Atmos. Sol. Terr. Phys., 59, , Hooper, D. A., and L. Thomas, Complementary criteria for identifying regions of intense atmospheric turbulence using lower VHF radar, J. Atmos. Sol. Terr. Phys., 60, 49 61, Jain, A. R., Y. Jaya Rao, P. B. Rao, G. Viswantathan, S. H. Damle, P. Balamuralidhar, and A. Kulkarni, Preliminary observations using ST mode of the Indian MST radar: Detecting the signature of the tropopause, J. Atmos. Terr. Phys., 56, , Jain, A. R., Y. Jaya Rao, P. B. Rao, V. K. Anandan, S. H. Damle, P. Balamuralidhar, A. Kulakerni, and G. Viswanathan, Indian MST radar, 2, First scientific results in ST mode, Radio Sci., 30, , Jain, A. R., and N. S. Mydhili, Height-time-structure of VHF backscatter from stable and turbulently mixed atmosphere layers at tropical latitudes, J. Atmos. Sol. Terr. Phys., 63, , Kurosaki, S., M. D. Yamanaka, H. Hashiguchi, T. Sato, and S. Fukao, Vertical eddy diffusivity in the lower and middle atmosphere: A climatology based on the MU radar observations during , J. Atmos. Terr. Phys., 58, , Lilly, D. K., D. E. Waco, and S. I. Adelfang, Stratospheric mixing estimated from high-altitude turbulence measurements, J. Appl. Meteorol., 13, , Lubken, F. J., On the extraction of turbulent parameters from atmospheric density fluctuations, J. Geophys. Res., 97, 20,385 20,395, Lubken, F. J., U. von Zahn, E. V. Thrane, T. A. Blix, G. A. Kokin, and S. V. Pachomov, In situ measurements of turbulence energy dissipation rate and eddy diffusion coefficients during MAP/WINE, J. Atmos. Terr. Phys., 49, , Narayana Rao, D., P. Kishore, T. Narayana Rao, S. Vijaya Bhaskara Rao, K. Krishna Reddy, M. Yarraiah, and M. Hareesh, Studies on refractivity structure constant, eddy dissipation rate and momentum flux at a tropical latitude, Radio Sci., 32, , Nastrom, G. D., Doppler radar spectral width broadening due to beam width and wind shear, Ann. Geophys., 15, , Nastrom, G. D., and F. D. Eaton, Turbulence eddy dissipation rates from radar observations at 5 20 km at White Sand Missile Range, New Mexico, J. Geophys. Res., 102, 19,495 19,506, 1997a. Nastrom, G. D., and F. D. Eaton, A brief climatology of eddy diffusivities over White Sand Missile Range, New Mexico, J. Geophys. Res., 102, 29,819 29,826, 1997b. Nastrom, G. D., K. S. Gage, and W. L. Ecklund, Variability of turbulence, 4 20 km, in Colorado and Alaska from MST radar observations, J. Geophys. Res., 91, , Rao, P. B., A. R. Jain, P. Kishore, P. Balamuralidhar, S. H. Damle, and G. Viswanathan, Indian MST radar, 1, System description and sample vector wind measurements in ST mode, Radio Sci., 30, , Sasi, M. N., A reference atmosphere for the Indian equatorial zone, Indian J. Radio Space Phys., 23, , Sasi, M. N., and K. S. Gupta, A reference atmosphere for Indian equatorial zone from surface to 80 km-1985, Sci. Rep. SPL:SR:006:85, Space Phys. Lab., Vikram Sarabhi Space Cent., Trivandrum, India, Sato, T., and R. F. Woodman, Fine altitude resolution observations of stratospheric turbulent layers by the Arecibo 430- MHz radar, J. Atmos. Sci., 39, , Sato, T., T. Tsuda, S. Kato, S. Morimoto, S. Fukao, and I. Kimura, High-resolution MST observations of turbulence using the MU radar, Radio Sci., 20, , Sato, T., H. Matsumoto, S. Fukao, and S. Kato, Tropospheric turbulence parameters measured by using the MU radar, in MAP Handbook, vol. 20, edited by S. A. Bowhill and B. Edwards, pp , Secr., Sci. Comm. on Sol.-Terr. Phys., Univ. of Ill., Urbana, Teitelbaum, H., and J. Blamont, Variations of turbopause altitude during the night, Planet. Space Sci., 25, , Thrane, E. V., O. Andreassen, T. A. Blix, B. Grandal, A. Brekke, C. R. Philbrick, F. J. Schmidtlin, H. U. Widdel, U. von Zahn, and F. J. Lubken, Neutral air turbulence in the upper atmosphere observed during the energy budget campaign, J. Atmos. Terr. Phys., 49, , Thrane, E. V., T. A. Blix, C. Hall, T. L. Hansen, U. von Zahn, W. Meyer, P. Czechowsky, G. Schmidt, H. U. Widdel, and A. Neumann, Small scale structure and turbulence in the

12 14-12 GHOSH ET AL.: MST RADAR AND RADIOSONDE MEASUREMENTS, 2 mesosphere and lower thermosphere at high latitudes in winter, J. Atmos. Terr. Phys., 49, , Vinnichenko, N. K., N. Z. Pinus, S. M. Shmater, and G. N. Shur, Turbulence in the Free Atmosphere, translated from Russian by J. A. Dutton, Consult. Bur., New York, Weinstock, J., On the theory of turbulence in the buoyancy subrange of stratified flows, J. Atmos. Sci., 35, , Weinstock, J., Vertical turbulence diffusivity for weak or strong stable stratification, J. Geophys. Res., 86, , Woodman, R. F., and P. K. Rastogi, Evaluation of effective eddy diffusive coefficients using radar observations of turbulence in the stratosphere, Geophys. Res. Lett., 11, , Worthington, R. M., R. D. Palmer, and S. Fukao, Complete maps of the aspect sensitivity of VHF atmospheric radar echoes, Ann. Geophys., 17, , Yamanaka, M. D., H. Tanaka, H. Hirosawa, Y. Matsuzaka, T. Yamagani, and J. Nishimura, Measurement of stratospheric turbulence by balloon-borne glow-discharge anemometer, J. Meteorol. Soc. Jpn., 63, , A. K. Ghosh, A. R. Jain, and V. Sivakumar, National MST Radar Facility, P.B. 123, Tirupati, AP, India. (nmrf@ isro.ernet.in)