Dynamical Characteristics of Cirrus Clouds from Aircraft and Radar Observations in Micro and Meso-γ Scales

I. Gultepe Cloud Physics Research Division AES Downsview, Ontario, Canada.

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D. O'C. Starr NASA/GSFC, Greenbelt, Maryland.

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A. J. Heymsfield NCAR. Boulder, Colorado.

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T. Uttal NOAA/ETL, Boulder, Colorado.

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T. P. Ackerman The Pennsylvania State University, University Park Pennsylvania.

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D. L. WestPhal NASA/Ames Research Center, Moffett Field California.

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Abstract

Cirrus clouds that formed on 26 November and 6 December 1991 during the First International Satellite Cloud Climatology Project Regional Experiment (FIRE) II, which took place over the Kansas region. are studied because of significant dynamic activity in the micro (<1 km) and meso γ (<25 km) scales within the cloud. Observations are obtained from the NCAR King Air, NOAA Doppler, and PSU conventional radar. For this reason coherent structures (e.g., cells, vortex) that transfer significant heat, moisture, and turbulence are analyzed using aircraft and radar observations. Aircraft data is collected at 20 Hz, and calculations are made at two different scales. Scale separation is chosen at about 1 km. A coherence analysis technique is used to specify the correlation between temperature and vertical velocity w fluctuations. A swirling coefficient, indicating spirality, is calculated to better understand cloud dynamics. Sensible heat, latent heat, and radiative fluxes are compared with each other in two scales. Results showed that dynamic activity, including w about ±1.5 m s−1, and mean sensible heat fluxes (SHFs) and latent heat fluxes (LHFs) ∼10 W m−2 is estimated to be much larger for the 26 November case compared to the 6 December case. The swirling coefficient is estimated to be larger in upper and lower levels compared to those in middle levels for both days. Individual values of SHFs and LHFs are also found to be comparable with those of FIRE I. The size of coherent structures is estimated from aircraft and radar measurements to be about 0.5 and 3.5 km.

Abstract

Cirrus clouds that formed on 26 November and 6 December 1991 during the First International Satellite Cloud Climatology Project Regional Experiment (FIRE) II, which took place over the Kansas region. are studied because of significant dynamic activity in the micro (<1 km) and meso γ (<25 km) scales within the cloud. Observations are obtained from the NCAR King Air, NOAA Doppler, and PSU conventional radar. For this reason coherent structures (e.g., cells, vortex) that transfer significant heat, moisture, and turbulence are analyzed using aircraft and radar observations. Aircraft data is collected at 20 Hz, and calculations are made at two different scales. Scale separation is chosen at about 1 km. A coherence analysis technique is used to specify the correlation between temperature and vertical velocity w fluctuations. A swirling coefficient, indicating spirality, is calculated to better understand cloud dynamics. Sensible heat, latent heat, and radiative fluxes are compared with each other in two scales. Results showed that dynamic activity, including w about ±1.5 m s−1, and mean sensible heat fluxes (SHFs) and latent heat fluxes (LHFs) ∼10 W m−2 is estimated to be much larger for the 26 November case compared to the 6 December case. The swirling coefficient is estimated to be larger in upper and lower levels compared to those in middle levels for both days. Individual values of SHFs and LHFs are also found to be comparable with those of FIRE I. The size of coherent structures is estimated from aircraft and radar measurements to be about 0.5 and 3.5 km.

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