STUDY ON THE RELATIONSHIP BETWEEN ROUGHNESS PARAMETERS AND VERTICAL WIND VELOCITY PROFILES OVER AN URBAN AREA BY LES

AbstractRainfall velocity, raindrop size distribution (DSD), and vertical wind velocity were simultaneously observed with 2.05- and 1.54-μm coherent Doppler lidars during convective and stratiform rain events. A retrieval method is based on identifying two separate spectra from the convolution of the aerosol and precipitation Doppler lidar spectra. The vertical wind velocity was retrieved from the aerosol spectrum peak and then the terminal rainfall velocity corrected by the vertical air motion from the precipitation spectrum peak was obtained. The DSD was derived from the precipitation spectrum using the relationship between the raindrop size and the terminal rainfall velocity. A comparison of the 1-min-averaged rainfall velocity from Doppler lidar measurements at a minimum range and that from a collocated ground-based optical disdrometer revealed high correlation coefficients of over 0.89 for both convective and stratiform rain events. The 1-min-averaged DSDs retrieved from the Doppler lidar spectrum using parametric and nonparametric methods are also in good agreement with those measured with the optical disdrometer with a correlation coefficient of over 0.80 for all rain events. To retrieve the DSD, the parametric method assumes a mathematical function for the DSD and the nonparametric method computes the direct deconvolution of the measured Doppler lidar spectrum without assuming a DSD function. It is confirmed that the Doppler lidar can retrieve the rainfall velocity and DSD during relatively heavy rain, whereas the ratio of valid data significantly decreases in light rain events because it is extremely difficult to separate the overlapping rain and aerosol peaks in the Doppler spectrum.

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A relaxed eddy accumulation system for measuring vertical fluxes of nitrous acid

Atmospheric Measurement Techniques ◽

10.5194/amt-4-2093-2011 ◽

2011 ◽

Vol 4 (10) ◽

pp. 2093-2103 ◽

Cited By ~ 56

Author(s):

X. Ren ◽

J. E. Sanders ◽

A. Rajendran ◽

R. J. Weber ◽

A. H. Goldstein ◽

...

Keyword(s):

Wind Velocity ◽

Nitrous Acid ◽

Sonic Anemometer ◽

Field Studies ◽

Fast Response ◽

Vertical Wind ◽

Measured Temperature ◽

Relaxed Eddy Accumulation ◽

Vertical Fluxes ◽

Vertical Wind Velocity

Abstract. A relaxed eddy accumulation (REA) system combined with a nitrous acid (HONO) analyzer was developed to measure atmospheric HONO vertical fluxes. The system consists of three major components: (1) a fast-response sonic anemometer measuring both vertical wind velocity and air temperature, (2) a fast-response controlling unit separating air motions into updraft and downdraft samplers by the sign of vertical wind velocity, and (3) a highly sensitive HONO analyzer based on aqueous long path absorption photometry that measures HONO concentrations in the updrafts and downdrafts. A dynamic velocity threshold (±0.5σw, where σw is a standard deviation of the vertical wind velocity) was used for valve switching determined by the running means and standard deviations of the vertical wind velocity. Using measured temperature as a tracer and the average values from two field deployments, the flux proportionality coefficient, β, was determined to be 0.42 ± 0.02, in good agreement with the theoretical estimation. The REA system was deployed in two ground-based field studies. In the California Research at the Nexus of Air Quality and Climate Change (CalNex) study in Bakersfield, California in summer 2010, measured HONO fluxes appeared to be upward during the day and were close to zero at night. The upward HONO flux was highly correlated to the product of NO2 and solar radiation. During the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX 2009) at Blodgett Forest, California in July 2009, the overall HONO fluxes were small in magnitude and were close to zero. Causes for the different HONO fluxes in the two different environments are briefly discussed.

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A relaxed eddy accumulation system for measuring vertical fluxes of nitrous acid

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-4-4105-2011 ◽

2011 ◽

Vol 4 (3) ◽

pp. 4105-4130 ◽

Cited By ~ 1

Author(s):

X. Ren ◽

J. E. Sanders ◽

A. Rajendran ◽

R. J. Weber ◽

A. H. Goldstein ◽

...

Keyword(s):

Wind Velocity ◽

Nitrous Acid ◽

Sonic Anemometer ◽

Field Studies ◽

Fast Response ◽

Vertical Wind ◽

Measured Temperature ◽

Relaxed Eddy Accumulation ◽

Vertical Fluxes ◽

Vertical Wind Velocity

Abstract. A relaxed eddy accumulation (REA) system combined with a nitrous acid (HONO) analyzer was developed to measure atmosperhic HONO vertical fluxes. The system consists of three major components: (1) a fast-response sonic anemometer measuring vertical wind velocity and air temperature, (2) a fast-response controlling unit separating air motions into updraft and downdraft samplers by the sign of vertical wind velocity, and (3) a highly sensitive HONO analyzer based on aqueous long path absorption photometry measuring HONO concentations in these updrafts and downdrafts. A dynamic velocity threshold (±0.5σw, where σw is a standard deviation of the vertical wind velocity) was used for valve switching determined by the running means and standard deviations of the vertical wind velocity. Using measured temperature as a tracer and the average values from two field deployments, the flux proportionality coefficient, β, was determined to be 0.42 ± 0.02, in good agreement with the theoretical estimation. The REA system was deployed in two ground-based field studies. In the California Research at the Nexus of Air Quality and Climate Change (CalNex) study in Bakersfield, California in summer 2010, measured HONO fluxes appeared to be upward during the day and were close to zero at night. The upward HONO flux was highly correlated to the product of NO2 and solar radiation. During the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX 2009) at Blodgett Forest, California in July 2009, the overall HONO fluxes were small in magnitude and were close to zero. Causes for the differences in HONO fluxes in the two different environments are briefly discussed.

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