Mesoscale pressure waves, including atmospheric gravity waves, outflow and frontal passages, and ... more Mesoscale pressure waves, including atmospheric gravity waves, outflow and frontal passages, and wake lows, are outputs of and can potentially modify clouds and precipitation. The vertical motions associated with these waves can modify the temperature and relative humidity of air parcels and thus yield potentially irreversible changes to the cloud and precipitation content of those parcels. A wavelet-based method for identifying and tracking these types of wave signals in time series data from networks of low-cost, highprecision (0.8 Pa noise floor, 1 Hz recording frequency) pressure sensors is demonstrated. Strong wavelet signals are identified using a wave-period-dependent (i.e., frequencydependent) threshold, and then those signals are extracted by inverting the wavelet transform. Wave periods between 1 and 120 min were analyzed-a range which could capture acoustic, acoustic-gravity, and gravity wave modes. After extracting the signals from a network of pressure sensors, the cross-correlation function is used to estimate the time difference between the wave passage at each pressure sensor. From those time differences, the wave phase velocity vector is calculated using a least-squares fit. If the fitting error is sufficiently small (thresholds of RMSE < 90 s and NRMSE < 0.1 were used), then a wave event is considered robust and trackable. We present examples of tracked wave events, including a Lamb wave caused by the Hunga Tonga volcanic eruption in January 2020, a gravity wave train, an outflow boundary passage, a frontal passage, and a cold front passage. The data and processing techniques presented here can have research applications in wave climatology and testing associations between waves and atmospheric phenomena.
Quarterly Journal of the Royal Meteorological Society, Oct 1, 2004
Ship-based radar measurements obtained during the East Pacific Investigation of Climate 2001 stra... more Ship-based radar measurements obtained during the East Pacific Investigation of Climate 2001 stratocumulus (Sc) cruise are used to derive characteristics of the rainfall from drizzling Sc. Reflectivity to rain rate (Z-R) relationships are determined from shipboard raindrop-size distribution measurements obtained from observations using filter-paper, and compared to Z-R relationships derived from aircraft probe data from below northeast Atlantic drizzling Sc and stratus. A model for the evaporation and sedimentation of drizzle is combined with reflectivity profiles from a millimetre-wavelength cloud radar to derive information on the mean raindrop radius and drizzle drop concentrations at cloud base, and to show how Z-R relationships change with height below the cloud base. The Z-R relationships are used in conjunction with shipborne C-band radar reflectivity data to estimate areal average precipitation with uncertainties at cloud base and at the surface. In the Sc drizzle Z-R relationship, Z = aR b (where a and b are constants), the estimated exponent b = 1.1 to 1.4 is lower than commonly observed in deep convective rain (b = 1.5). Analyses indicate that variations in Sc rain rates and reflectivities are influenced both by fluctuations in drizzle drop concentration and in mean radius, but that number concentration contributes more to the modulation of rain rate in Sc. Rain rates derived using the scanning C-band radar are found to be spatially variable, with much of the accumulation originating from a small fraction of the drizzling area. The observations also suggest that rain rate in marine Sc is strongly dependent on cloud liquidwater path, and inversely correlated with cloud droplet concentration.
Data Overview AMSR V002 • AE_L2A AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temp... more Data Overview AMSR V002 • AE_L2A AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temperatures • AE_Ocean AMSR-E/Aqua L2B Global Swath Ocean Products derived from Wentz Algorithm MODIS Series 51 • MYD06_L2 Aqua MODIS Level 2 Cloud Product Introduction Marine stratocumulus clouds are important sources of net cooling in the global radiation budget and are poorly represented in global climate models. Several field studies have shown that drizzle has a role in modulating low cloud mesoscale structures, cloud fraction and albedo. In this work, we use an 89 GHz passive microwave emission algorithm to document the spatial frequency of drizzle occurrence during the day and at night off the coasts of California, Peru and Namibia for the period 2002-2011 (the entire AMSR-E data set). The resulting climatology is more comprehensive than previous work using the Cloudsat radar and allows us to do regional as well as interannual comparisons. Fig. 2. MODIS visible images of stratocumulus cloud decks in each area of interest a) off the coast of California on 24 July 2009 at 21:40 UTC, b) off the coast of Peru on 3 September 2009 at 19:45 UTC and c) off the coast of Namibia on 11 October 2009 at 14:10 UTC.
The Kwajalein, Marshall Islands, Tropical Rainfall Measuring Mission (TRMM) ground validation rad... more The Kwajalein, Marshall Islands, Tropical Rainfall Measuring Mission (TRMM) ground validation radar has provided a multiyear three-dimensional radar dataset at an oceanic site. Extensive rain gauge networks are not feasible over the ocean and, hence, are not available to aid in calibrating the radar or determining a conversion from reflectivity to rain rate. This paper describes methods used to ensure the calibration and allow the computation of quantitative rain maps from the radar data without the aid of rain gauges. Calibration adjustments are made by comparison with the TRMM satelliteborne precipitation radar. The additional steps required to convert the calibrated reflectivity to rain maps are the following: correction for the vertical profile of reflectivity below the lowest elevation angle using climatological convective and stratiform reflectivity profiles; conversion of reflectivity (Z) to rain rate (R) with a relationship based on disdrometer data collected at Kwajalein, and a gap-filling estimate. The time series of rain maps computed by these procedures include low, best, and high estimates to frame the estimated overall uncertainty in the radar rain estimation. The greatest uncertainty of the rain maps lies in the calibration of the radar (Ϯ30%). The estimation of the low-altitude vertical profile of reflectivity is also a major uncertainty (Ϯ15%). The Z-R and data-gap uncertainties are relatively minor (Ϯ5% or less). These uncertainties help to prioritize the issues that need to be addressed to improve quantitative rainfall mapping over the ocean and provide useful bounds when comparing radar-derived rain estimates with other remotely sensed measures of oceanic rain (such as from satellite passive microwave sensors).
Data projects pertaining to KWAJEX are described.Data sets delivered to the Goddard Distributed A... more Data projects pertaining to KWAJEX are described.Data sets delivered to the Goddard Distributed Active Archive Center (DAAC): 1) Kwajalein Experiment (KWAJEX) S-band calibrated, quality-controlled radar data, 1221 1 files of 3D volume data and 6832 files of 2D low-level reflectivity. 2) Raw and quality-control- processed versions of University of Washington Joss-Waldvogel disdrometer measurements obtained during KWAJEX. 3) A time series of synoptic-scale gif images of the Geostationary Meteorological Satellite (GMS) IR data for the KWAJEX period. The GMS satellite data set for the KWAJEX period was obtained from the University of Wisconsin and reprocessed into format amenable for comparison with radar data.Aircraft microphysics flight-leg definitions for all aircraft and all missions during KWAJEX were completed to facilitate microphysics data processing.
ABSTRACT A unique combination of satellite and shipborne Doppler radar data from the 2001 East Pa... more ABSTRACT A unique combination of satellite and shipborne Doppler radar data from the 2001 East Pacific Investigation of Climate Stratocumulus (EPIC Sc) field experiment are examined to study the characteristics of marine stratocumulus drizzle cells. Infrared satellite images are used to classify the cloud structures into closed cellular, open cellular, or unclassifiable categories. Both horizontal and vertical cross sections of radar reflectivity and radial velocity are used to characterize the microphysical and kinematic structures of the drizzle cells. Distributions of drizzle cell structure, size, and intensity are similar among the cloud structure categories, though the open-cellular distributions are shifted toward higher values. Stronger and larger drizzle cells preferentially occur when the cloud field is broken (open-cellular and unclassifiable categories). Individual drizzle cells about 2-20 km across usually showed precipitation growth within the cloud layer and evaporation below, divergence near echo top, and convergence below cloud base. Diverging flow near the surface was also observed beneath heavily precipitating drizzle cells. As the cloud field transitioned from a closed to an open-cellular cloud structure, shipborne radar revealed prolific development of small drizzle cells (
Raindrop images obtained on research flights of the NCAR Electra aircraft in the Tropical Oceans ... more Raindrop images obtained on research flights of the NCAR Electra aircraft in the Tropical Oceans Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) are analyzed. The drop size distributions, based on the images obtained in 6-s samples (about 750 m of flight track), are used to calculate both radar reflectivity Z and rain rate R. Airborne radar data from the NOAA P-3 aircraft flying in coordination with the Electra are used to categorize the particle-image data according to whether the drop images were obtained in regions of convective or stratiform precipitation. Within stratiform precipitation, the same rain rate could be produced by a drop spectrum dominated by numerous small drops (lower reflectivity) or by a few large drops (higher reflectivity). The reflectivity values varied by as much as 9 dB for a given rain rate. Reflectivity data from the airborne radar and flight-level data reveal that the stratiform regions often contain fallstreaks of about 0.1-2 km in horizontal dimension. The fallstreaks are associated with large-drop spectra and local maxima in reflectivity up to approximately 40 dBZ and in rain rates up to 25 mm h Ϫ1. The fallstreaks extend downward from the melting band and bend with the low-level wind shear, but do not usually reach the surface. Thus, although relatively more uniform than convective regions, stratiform regions can be variable in reflectivity and rain rate at fine spatial scales in both the horizontal and vertical directions. Stratiform regions are therefore best characterized by their ensemble properties rather than the values of individual high-resolution measurements. The variability of stratiform drop size spectra arises primarily from the occurrence of fallstreaks and the discontinuous nature of regions favoring aggregation of snow crystals, and it implies that Z-R distributions associated with convective and stratiform precipitation are not statistically distinct. Thus, separate Z-R relations for convective and stratiform precipitation are not justified, and techniques to distinguish between convective and stratiform precipitation based solely on the characteristics of drop size distributions are not likely to be accurate. The variability of the drop size spectra in tropical precipitation makes an exponential fit to the Z-R relation sensitive to the spatial scale over which Z and R are determined. This sensitivity can be avoided by using a probability-matched Z-R relation. The probability-matched Z-R relation for all the raindrop image data from the Electra collected between altitudes of 2.7 and 3.3 km in TOGA COARE is similar to the Z-R relation obtained at the sea surface in the Global Atmospheric Research Program Atlantic Tropical Experiment.
Acquisition of accurate raindrop fall speed measurements outdoors in natural rain by means of mod... more Acquisition of accurate raindrop fall speed measurements outdoors in natural rain by means of moderatecost and easy-to-use devices represents a long-standing and challenging issue in the meteorological community. Feasibility experiments were conducted to evaluate the indoor accuracy of fall speed measurements made with a high-speed camera and to evaluate its capability for outdoor applications. An indoor experiment operating in calm conditions showed that the high-speed imaging technique can provide fall speed measurements with a mean error of 4.1-9.7 % compared to Gunn and Kinzer's empirical fall-speed-size relationship for typical sizes of rain and drizzle drops. Results obtained using the same apparatus outside in summer afternoon showers indicated larger positive and negative velocity deviations compared to the indoor measurements. These observed deviations suggest that ambient flow and turbulence play a role in modifying drop fall speeds which can be quantified with future outdoor high-speed camera measurements. Because the fall speed measurements, as presented in this article, are analyzed on the basis of tracking individual, specific raindrops, sampling uncertainties commonly found in the widely adopted optical disdrometers can be significantly mitigated.
Mesoscale pressure waves, including atmospheric gravity waves, outflow and frontal passages, and ... more Mesoscale pressure waves, including atmospheric gravity waves, outflow and frontal passages, and wake lows, are outputs of and can potentially modify clouds and precipitation. The vertical motions associated with these waves can modify the temperature and relative humidity of air parcels and thus yield potentially irreversible changes to the cloud and precipitation content of those parcels. A wavelet-based method for identifying and tracking these types of wave signals in time series data from networks of low-cost, highprecision (0.8 Pa noise floor, 1 Hz recording frequency) pressure sensors is demonstrated. Strong wavelet signals are identified using a wave-period-dependent (i.e., frequencydependent) threshold, and then those signals are extracted by inverting the wavelet transform. Wave periods between 1 and 120 min were analyzed-a range which could capture acoustic, acoustic-gravity, and gravity wave modes. After extracting the signals from a network of pressure sensors, the cross-correlation function is used to estimate the time difference between the wave passage at each pressure sensor. From those time differences, the wave phase velocity vector is calculated using a least-squares fit. If the fitting error is sufficiently small (thresholds of RMSE < 90 s and NRMSE < 0.1 were used), then a wave event is considered robust and trackable. We present examples of tracked wave events, including a Lamb wave caused by the Hunga Tonga volcanic eruption in January 2020, a gravity wave train, an outflow boundary passage, a frontal passage, and a cold front passage. The data and processing techniques presented here can have research applications in wave climatology and testing associations between waves and atmospheric phenomena.
Quarterly Journal of the Royal Meteorological Society, Oct 1, 2004
Ship-based radar measurements obtained during the East Pacific Investigation of Climate 2001 stra... more Ship-based radar measurements obtained during the East Pacific Investigation of Climate 2001 stratocumulus (Sc) cruise are used to derive characteristics of the rainfall from drizzling Sc. Reflectivity to rain rate (Z-R) relationships are determined from shipboard raindrop-size distribution measurements obtained from observations using filter-paper, and compared to Z-R relationships derived from aircraft probe data from below northeast Atlantic drizzling Sc and stratus. A model for the evaporation and sedimentation of drizzle is combined with reflectivity profiles from a millimetre-wavelength cloud radar to derive information on the mean raindrop radius and drizzle drop concentrations at cloud base, and to show how Z-R relationships change with height below the cloud base. The Z-R relationships are used in conjunction with shipborne C-band radar reflectivity data to estimate areal average precipitation with uncertainties at cloud base and at the surface. In the Sc drizzle Z-R relationship, Z = aR b (where a and b are constants), the estimated exponent b = 1.1 to 1.4 is lower than commonly observed in deep convective rain (b = 1.5). Analyses indicate that variations in Sc rain rates and reflectivities are influenced both by fluctuations in drizzle drop concentration and in mean radius, but that number concentration contributes more to the modulation of rain rate in Sc. Rain rates derived using the scanning C-band radar are found to be spatially variable, with much of the accumulation originating from a small fraction of the drizzling area. The observations also suggest that rain rate in marine Sc is strongly dependent on cloud liquidwater path, and inversely correlated with cloud droplet concentration.
Data Overview AMSR V002 • AE_L2A AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temp... more Data Overview AMSR V002 • AE_L2A AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temperatures • AE_Ocean AMSR-E/Aqua L2B Global Swath Ocean Products derived from Wentz Algorithm MODIS Series 51 • MYD06_L2 Aqua MODIS Level 2 Cloud Product Introduction Marine stratocumulus clouds are important sources of net cooling in the global radiation budget and are poorly represented in global climate models. Several field studies have shown that drizzle has a role in modulating low cloud mesoscale structures, cloud fraction and albedo. In this work, we use an 89 GHz passive microwave emission algorithm to document the spatial frequency of drizzle occurrence during the day and at night off the coasts of California, Peru and Namibia for the period 2002-2011 (the entire AMSR-E data set). The resulting climatology is more comprehensive than previous work using the Cloudsat radar and allows us to do regional as well as interannual comparisons. Fig. 2. MODIS visible images of stratocumulus cloud decks in each area of interest a) off the coast of California on 24 July 2009 at 21:40 UTC, b) off the coast of Peru on 3 September 2009 at 19:45 UTC and c) off the coast of Namibia on 11 October 2009 at 14:10 UTC.
The Kwajalein, Marshall Islands, Tropical Rainfall Measuring Mission (TRMM) ground validation rad... more The Kwajalein, Marshall Islands, Tropical Rainfall Measuring Mission (TRMM) ground validation radar has provided a multiyear three-dimensional radar dataset at an oceanic site. Extensive rain gauge networks are not feasible over the ocean and, hence, are not available to aid in calibrating the radar or determining a conversion from reflectivity to rain rate. This paper describes methods used to ensure the calibration and allow the computation of quantitative rain maps from the radar data without the aid of rain gauges. Calibration adjustments are made by comparison with the TRMM satelliteborne precipitation radar. The additional steps required to convert the calibrated reflectivity to rain maps are the following: correction for the vertical profile of reflectivity below the lowest elevation angle using climatological convective and stratiform reflectivity profiles; conversion of reflectivity (Z) to rain rate (R) with a relationship based on disdrometer data collected at Kwajalein, and a gap-filling estimate. The time series of rain maps computed by these procedures include low, best, and high estimates to frame the estimated overall uncertainty in the radar rain estimation. The greatest uncertainty of the rain maps lies in the calibration of the radar (Ϯ30%). The estimation of the low-altitude vertical profile of reflectivity is also a major uncertainty (Ϯ15%). The Z-R and data-gap uncertainties are relatively minor (Ϯ5% or less). These uncertainties help to prioritize the issues that need to be addressed to improve quantitative rainfall mapping over the ocean and provide useful bounds when comparing radar-derived rain estimates with other remotely sensed measures of oceanic rain (such as from satellite passive microwave sensors).
Data projects pertaining to KWAJEX are described.Data sets delivered to the Goddard Distributed A... more Data projects pertaining to KWAJEX are described.Data sets delivered to the Goddard Distributed Active Archive Center (DAAC): 1) Kwajalein Experiment (KWAJEX) S-band calibrated, quality-controlled radar data, 1221 1 files of 3D volume data and 6832 files of 2D low-level reflectivity. 2) Raw and quality-control- processed versions of University of Washington Joss-Waldvogel disdrometer measurements obtained during KWAJEX. 3) A time series of synoptic-scale gif images of the Geostationary Meteorological Satellite (GMS) IR data for the KWAJEX period. The GMS satellite data set for the KWAJEX period was obtained from the University of Wisconsin and reprocessed into format amenable for comparison with radar data.Aircraft microphysics flight-leg definitions for all aircraft and all missions during KWAJEX were completed to facilitate microphysics data processing.
ABSTRACT A unique combination of satellite and shipborne Doppler radar data from the 2001 East Pa... more ABSTRACT A unique combination of satellite and shipborne Doppler radar data from the 2001 East Pacific Investigation of Climate Stratocumulus (EPIC Sc) field experiment are examined to study the characteristics of marine stratocumulus drizzle cells. Infrared satellite images are used to classify the cloud structures into closed cellular, open cellular, or unclassifiable categories. Both horizontal and vertical cross sections of radar reflectivity and radial velocity are used to characterize the microphysical and kinematic structures of the drizzle cells. Distributions of drizzle cell structure, size, and intensity are similar among the cloud structure categories, though the open-cellular distributions are shifted toward higher values. Stronger and larger drizzle cells preferentially occur when the cloud field is broken (open-cellular and unclassifiable categories). Individual drizzle cells about 2-20 km across usually showed precipitation growth within the cloud layer and evaporation below, divergence near echo top, and convergence below cloud base. Diverging flow near the surface was also observed beneath heavily precipitating drizzle cells. As the cloud field transitioned from a closed to an open-cellular cloud structure, shipborne radar revealed prolific development of small drizzle cells (
Raindrop images obtained on research flights of the NCAR Electra aircraft in the Tropical Oceans ... more Raindrop images obtained on research flights of the NCAR Electra aircraft in the Tropical Oceans Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) are analyzed. The drop size distributions, based on the images obtained in 6-s samples (about 750 m of flight track), are used to calculate both radar reflectivity Z and rain rate R. Airborne radar data from the NOAA P-3 aircraft flying in coordination with the Electra are used to categorize the particle-image data according to whether the drop images were obtained in regions of convective or stratiform precipitation. Within stratiform precipitation, the same rain rate could be produced by a drop spectrum dominated by numerous small drops (lower reflectivity) or by a few large drops (higher reflectivity). The reflectivity values varied by as much as 9 dB for a given rain rate. Reflectivity data from the airborne radar and flight-level data reveal that the stratiform regions often contain fallstreaks of about 0.1-2 km in horizontal dimension. The fallstreaks are associated with large-drop spectra and local maxima in reflectivity up to approximately 40 dBZ and in rain rates up to 25 mm h Ϫ1. The fallstreaks extend downward from the melting band and bend with the low-level wind shear, but do not usually reach the surface. Thus, although relatively more uniform than convective regions, stratiform regions can be variable in reflectivity and rain rate at fine spatial scales in both the horizontal and vertical directions. Stratiform regions are therefore best characterized by their ensemble properties rather than the values of individual high-resolution measurements. The variability of stratiform drop size spectra arises primarily from the occurrence of fallstreaks and the discontinuous nature of regions favoring aggregation of snow crystals, and it implies that Z-R distributions associated with convective and stratiform precipitation are not statistically distinct. Thus, separate Z-R relations for convective and stratiform precipitation are not justified, and techniques to distinguish between convective and stratiform precipitation based solely on the characteristics of drop size distributions are not likely to be accurate. The variability of the drop size spectra in tropical precipitation makes an exponential fit to the Z-R relation sensitive to the spatial scale over which Z and R are determined. This sensitivity can be avoided by using a probability-matched Z-R relation. The probability-matched Z-R relation for all the raindrop image data from the Electra collected between altitudes of 2.7 and 3.3 km in TOGA COARE is similar to the Z-R relation obtained at the sea surface in the Global Atmospheric Research Program Atlantic Tropical Experiment.
Acquisition of accurate raindrop fall speed measurements outdoors in natural rain by means of mod... more Acquisition of accurate raindrop fall speed measurements outdoors in natural rain by means of moderatecost and easy-to-use devices represents a long-standing and challenging issue in the meteorological community. Feasibility experiments were conducted to evaluate the indoor accuracy of fall speed measurements made with a high-speed camera and to evaluate its capability for outdoor applications. An indoor experiment operating in calm conditions showed that the high-speed imaging technique can provide fall speed measurements with a mean error of 4.1-9.7 % compared to Gunn and Kinzer's empirical fall-speed-size relationship for typical sizes of rain and drizzle drops. Results obtained using the same apparatus outside in summer afternoon showers indicated larger positive and negative velocity deviations compared to the indoor measurements. These observed deviations suggest that ambient flow and turbulence play a role in modifying drop fall speeds which can be quantified with future outdoor high-speed camera measurements. Because the fall speed measurements, as presented in this article, are analyzed on the basis of tracking individual, specific raindrops, sampling uncertainties commonly found in the widely adopted optical disdrometers can be significantly mitigated.
Uploads
Papers by Sandra Yuter