Interactions between clear‐air reflective layers and rain observed with a boundary layer wind profiler

Cohn, Stephen A.; Rogers, Raymond R.; Jascourt, S.; Ecklund, W. L.; Carter, D. A.; Wilson, J. S.

doi:10.1029/94rs03168

Cited by 12 publications

(8 citation statements)

References 18 publications

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“…The solid region represents the contribution from rain, and the open region represents that from refractive index fluctuations. The disadvantages of this method are uncertainties in the estimations of power and spectral width, because of the overlapping of two echoes [Cohn et al, 1995]. This method does not assume any firing function for these two echoes.…”

Section: System Description and Data Analysismentioning

confidence: 99%

Tropical precipitating systems observed with Indian MST radar

Rao¹,

Rao²,

Raghavan³

1999

Radio Science

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Abstract. Three campaigns are conducted with the Indian mesosphere-stratosphere-troposphere (MST) radar, located at Gadanki (13.5øN, 79.2øE), India, to study the precipitating systems in the tropics. This study mainly deals with (1) classification of precipitating clouds and the spectral characteristics of echoes associated with these cloud systems and (2) characteristics of the radar bright band. The radar gets echoes scattered both from refractive index fluctuations and precipitation particles in moderate to heavy precipitation conditions. These echoes are separated in the spectral domain to determine the vertical air motion and the Doppler velocity ofhydrometeors simultaneously. The tropical precipitating systems are classified as stratiform and convective using the reflectivity and vertical velocity distribution. The echo power, spectral width, and vertical velocities of the ambient air and hydrometeors in both the cloud systems have been compared. Aspect sensitivity of the echoes from the hydrometeors and refractive index fluctuations in both stratiform and convective atmosphere is studied. A transition stage, where the stratiform precipitation is associated with the convection, is also reported. Backscattered power from precipitation particles is used to estimate the reflectivity factor (dBZ), and these values along with spectral width and vertical velocity values are used to identify the bright band structure. The reflectivity at the bright band, up to 42 dBZ, is found to be 10-12 dB more than the average value of reflectivity below the bright band. Discussion on the factors contributing to this enhancement is also included. A clear layered structure around the 0øC isotherm in the reflectivity profile of the precipitation echo confirms the presence of the bright band. The thickness of the bright band is estimated and is correlated with the peak reflectivity at the bright band. Comparison of the average terminal velocity of hydrometeors with their average Doppler velocities below the bright band shows the presence of gentle updrafts of a few cm s '• in stratiform precipitation. These studies are made for the first time with the Indian MST radar and also demonstrate the capability of a VHF radar in studying precipitating systems in addition to the turbulence to which these radars are highly sensitive.

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Section: System Description and Data Analysismentioning

confidence: 99%

Tropical precipitating systems observed with Indian MST radar

Rao¹,

Rao²,

Raghavan³

1999

Radio Science

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“…Whereas light rain or drizzle is all that is necessary for the return from hydrometeors to be larger than that from the clearair for UHF wind-profilers. While this is true in general, several studies (Chu and Lin, 1994;Cohn et al, 1995;Vaughan and Worthington, 2000;McDonald et al, 2004) have suggested that processes associated with precipitation can directly impact the magnitude of the clear-air signal. Chu and Lin (1994) indicated that heavy convective precipitation suppresses VHF radar clear-air returns which they attributed to the effect of entrainment of dry, cold air into a warm, moist cloud.…”

Section: Introductionmentioning

confidence: 90%

“…For example, Cohn et al (1995) made observations with a 915 MHz profiler in light precipitation and indicated that when rain or snow falls through a region of clear-air it modifies the humidity structure and possibly also influences the small-scale air circulation and thus may affect the returns. Their study focused on persistent clear air layers which can be examined before and during surface rainfall.…”

Section: Introductionmentioning

confidence: 99%

VHF signal power suppression in stratiform and convective precipitation

et al. 2006

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Abstract. Previous studies have indicated that VHF clear-air radar return strengths are reduced during periods of precipitation. This study aims to examine whether the type of precipitation, stratiform and convective precipitation types are identified, has any impact on the relationships previously observed and to examine the possible mechanisms which produce this phenomenon. This study uses a combination of UHF and VHF wind-profiler data to define periods associated with stratiform and convective precipitation. This identification is achieved using an algorithm which examines the range squared corrected signal to noise ratio of the UHF returns for a bright band signature for stratiform precipitation. Regions associated with convective rainfall have been defined by identifying regions of enhanced range corrected signal to noise ratio that do not display a bright band structure and that are relatively uniform until a region above the melting layer.This study uses a total of 68 days, which incorporated significant periods of surface rainfall, between 31 August 2000 and 28 February 2002 inclusive from Aberystwyth (52.4 • N, 4.1 • W). Examination suggests that both precipitation types produce similar magnitude reductions in VHF signal power on average. However, the frequency of occurrence of statistically significant reductions in VHF signal power are very different. In the altitude range 2-4 km stratiform precipitation is related to VHF signal suppression approximately 50% of the time while in convective precipitation suppression is observed only 27% of the time. This statistical result suggests that evaporation, which occurs more often in stratiform precipitation, is important in reducing the small-scale irregularities in humidity and thereby the radio refractive index. A detailed case study presented also suggests that evaporation reducing small-scale irregularities in humidity may contribute to the observed VHF signal suppression.

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“…Lidar has also successfully been used for ice/water discrimination (Sassen, 1991). Although the radar studies by Rogers et al and Gage et al were directed at precipitating clouds in the tropics, the use of profilers in cloud studies is more general (Gossard, 1994;Ralph, 1995;Cohn, 1995b). A recent summary of the use of radars to measure turbulence and microphysical parameters in marine boundary-layer stratus is given by White et al (1995a).…”

Section: Scalar Fluxesmentioning

confidence: 99%

Ground-based remote sensing of the atmospheric boundary layer: 25 years of progress

Wilczak

Gossard

Neff

et al. 1996

Boundary-Layer Meteorol

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The role of ground-based remote sensors in boundary-layer research is reviewed, emphasizing the contributions of radars, sodars, and lidars. The review begins with a brief comparison of the state of remote sensors in boundary-layer research 25 years ago with its present-day status. Next, a summary of the current capabilities of remote sensors for boundary-layer studies demonstrates that for boundary-layer depth and for profiles of many mean quantities, remote sensors offer some of the most accurate measurements available. Similar accuracies are in general not found for most turbulence parameters. Important contributions of remote sensors to our understanding of the structure and dynamics of various boundary-layer phenomena or processes are then discussed, including the sea breeze, convergence boundaries, dispersion, and boundary-layer cloud systems. The review concludes with a discussion of the likely future role of remote sensors in boundary-layer research.

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Interactions between clear‐air reflective layers and rain observed with a boundary layer wind profiler

Cited by 12 publications

References 18 publications

Tropical precipitating systems observed with Indian MST radar

Tropical precipitating systems observed with Indian MST radar

VHF signal power suppression in stratiform and convective precipitation

Ground-based remote sensing of the atmospheric boundary layer: 25 years of progress

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