Sodar observations of the nocturnal boundary layer at Kharagpur, India

Abstract

Sodar has been installed at Kharagpur (22.2" N, 87.3' E) as a part of the MONTBLEX-90 experiment and data were collected during the monsoon period. The variation of the nocturnal boundary layer (NBL) during the monsoon period is discussed. The height corresponding to the low-level wind maximum in the sodar wind profile during night time is identified as the NBL height. Mean monthly winds for July and August, plotted as time-height cross sections, reveal the height of the ground-based stable layer. The average NBL heights in the months of July and August are found to be 324 m and 296 m respectively. It is observed that the NBL height is relatively high in the month of July (active phase of monsoon) compared to that during August (weak phase). The months of July (total rainfall = 901 mm) and August (total rainfall = 134 mm) are associated with cloudy and relatively clear sky conditions. This indicates that clouds (through their effect on longwave cooling to space) play an important role in determining the NBL height during the monsoon.

A case study of atmospheric boundary layer features during winter over a tropical inland station — Kharagpur (22.32°N, 87.32°E)

“…Again on JD 354, NBL depth was high (105 m), but during the next three days it was relatively low (62 m to 70 m). From JD 359 to JD 362, NBL depth was more than 100 m and afterwards NBL depth was less than 80 m. The average NBL depth obtained for December 2004 is ∼ 75 m, from tethersonde flights carried out between 20:00 and 23:00 h. It may be noted that this value is much lower than the average NBL depths reported by Murthy et al (1996) for July (324 m) and August (296 m) using the SODAR data obtained during the MONTBLEX-90.…”

“…Parasnis and Morwal (1994) studied the thermodynamic features of the convective boundary layer using aerological observations at Calcutta, Bhubaneswar, New Delhi and Jodhpur obtained during MONTBLEX-90, and the mixed layer depths using SODAR observations over an inland station, Kharagpur were used to understand the saturation of mixed-layers after the onset phase of the monsoon. Murthy et al (1996) used the SODAR observations over Kharagpur to study the variation of the nocturnal boundary layer during monsoon period. Nonetheless, in the past there have been no in situ observations of ABL parameters during winter season over the IGP region.…”

A Climatological Study of the Nocturnal Boundary Layer over a Complex-Terrain Station

“…Only a few studies exist on NBL evolution and structure in the literature (Murthy et al 1996;Devara et al 1995). Murthy et al (1996) investigated the variation of NBL height in a monsoon season, using Doppler sodar observations over Kharagpur, as a part of the MONTBLEX-90 experiment. As can be noticed, none of the above studies discussed different types of NBL and their seasonal variation.…”

“…Traditionally, it is determined based on turbulence characteristics (Caughey et al 1979;Wyngaard 1986;Mahrt and Vickers 2006). The depth of the NBL can also be determined by using the low-level wind maxima (Stull 1988;Beyrich and Weill 1993;Murthy et al 1996). Beyrich and Weill (1993) estimated the NBL height based on digitized profiles of sound detection and ranging (sodar) backscattered echo intensity.…”

Vertical structure of the stable boundary layer detected by RASS-SODAR and in-situ measurements in SABLES 2006 field campaign

“…The presence of this phenomenon can be related to elevated turbulence (Banta et al 2002, Conangla and) and generation of gravity waves , Cuxart 2008. Some of the processes described above have been previously studied in the SBL by remote-sensing techniques, including SODAR measurements (Casadio et al 1996, Murthy et al 1996, Barlow et al 2011. Kniffka et al (2009) present statistical properties of SBL waves such as spatial coherences and frequency spectra determined by acoustic remote sensing methods, and estimate the anisotropy of the internal gravity waves.…”