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- Author or Editor: J. M. Lewis x
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Abstract
The spatial and temporal evolution of supercooled water fields in ten wintertime storm systems occurring over the northern Colorado Rocky Mountain region have been examined using data collected by the recently developed scanning dual-channel microwave radiometer. These data were supported by several independent datasets including vertically pointing radar data, mountaintop liquid water content measurements, low and high altitude measurements of crystal rime characteristic rawinsonde data and precipitation intensity measurements.
The ten case studies discussed in this paper represent various stages in the synoptic scale evolution of storms that affect the northern Colorado Rockies. Liquid water was found to occur in nearly all stages of most of these storms. The temporal variations in the magnitude of the liquid water content were significant.
Three common features concerning the evolution of the liquid water field were observed in the prefrontal cloud systems: 1) an inverse relationship between precipitation rate and liquid water content occurred; 2) a direct relationship between cloud top temperature and liquid water content was observed; and 3) the magnitude of the liquid water content was consistently higher over the mountain slopes.
In the postfrontal cloud systems studied, the liquid water content exhibited little variability upwind of the mountain base but varied considerably in the vicinity of the mountain. In these three storms, the magnitude of the liquid water content over the ridge was inversely related to the precipitation rate at mountain base. Liquid water production near the ridgeline was associated with both orographic and convective forcing.
Three orographic cloud systems are discussed in this paper. These clouds formed in similar synoptic environments. The three systems were shallow, had tops warmer than −22°C, and had limited horizontal extent. As in the previous cases, the changes in the liquid water field were inversely associated with changes in precipitation rate. In one case, a decrease in liquid water content was also associated with a decrease in cloud top temperature.
Abstract
The spatial and temporal evolution of supercooled water fields in ten wintertime storm systems occurring over the northern Colorado Rocky Mountain region have been examined using data collected by the recently developed scanning dual-channel microwave radiometer. These data were supported by several independent datasets including vertically pointing radar data, mountaintop liquid water content measurements, low and high altitude measurements of crystal rime characteristic rawinsonde data and precipitation intensity measurements.
The ten case studies discussed in this paper represent various stages in the synoptic scale evolution of storms that affect the northern Colorado Rockies. Liquid water was found to occur in nearly all stages of most of these storms. The temporal variations in the magnitude of the liquid water content were significant.
Three common features concerning the evolution of the liquid water field were observed in the prefrontal cloud systems: 1) an inverse relationship between precipitation rate and liquid water content occurred; 2) a direct relationship between cloud top temperature and liquid water content was observed; and 3) the magnitude of the liquid water content was consistently higher over the mountain slopes.
In the postfrontal cloud systems studied, the liquid water content exhibited little variability upwind of the mountain base but varied considerably in the vicinity of the mountain. In these three storms, the magnitude of the liquid water content over the ridge was inversely related to the precipitation rate at mountain base. Liquid water production near the ridgeline was associated with both orographic and convective forcing.
Three orographic cloud systems are discussed in this paper. These clouds formed in similar synoptic environments. The three systems were shallow, had tops warmer than −22°C, and had limited horizontal extent. As in the previous cases, the changes in the liquid water field were inversely associated with changes in precipitation rate. In one case, a decrease in liquid water content was also associated with a decrease in cloud top temperature.
Abstract
Cirrus cloud daytime top-of-the-atmosphere radiative forcing (TOA CRF) is estimated for a 2-yr NASA Micro-Pulse Lidar Network (532 nm; MPLNET) dataset collected at Fairbanks, Alaska. Two-year-averaged daytime TOA CRF is estimated to be between −1.08 and 0.78 W·m−2 (from −0.49 to 1.10 W·m−2 in 2017, and from −1.67 to 0.47 W·m−2 in 2018). This subarctic study completes a now trilogy of MPLNET ground-based cloud forcing investigations, following midlatitude and tropical studies by Campbell et al. at Greenbelt, Maryland, and Lolli et al. at Singapore. Campbell et al. hypothesize a global meridional daytime TOA CRF gradient that begins as positive at the equator (2.20–2.59 W·m−2 over land and from −0.46 to 0.42 W·m−2 over ocean at Singapore), becomes neutral in the midlatitudes (0.03–0.27 W·m−2 over land in Maryland), and turns negative moving poleward. This study does not completely confirm Campbell et al., as values are not found as exclusively negative. Evidence in historical reanalysis data suggests that daytime cirrus forcing in and around the subarctic likely once was exclusively negative. Increasing tropopause heights, inducing higher and colder cirrus, have likely increased regional forcing over the last 40 years. We hypothesize that subarctic interannual cloud variability is likely a considerable influence on global cirrus cloud forcing sensitivity, given the irregularity of polar versus midlatitude synoptic weather intrusions. This study and hypothesis lay the basis for an extrapolation of these MPLNET experiments to satellite-based lidar cirrus cloud datasets.
Abstract
Cirrus cloud daytime top-of-the-atmosphere radiative forcing (TOA CRF) is estimated for a 2-yr NASA Micro-Pulse Lidar Network (532 nm; MPLNET) dataset collected at Fairbanks, Alaska. Two-year-averaged daytime TOA CRF is estimated to be between −1.08 and 0.78 W·m−2 (from −0.49 to 1.10 W·m−2 in 2017, and from −1.67 to 0.47 W·m−2 in 2018). This subarctic study completes a now trilogy of MPLNET ground-based cloud forcing investigations, following midlatitude and tropical studies by Campbell et al. at Greenbelt, Maryland, and Lolli et al. at Singapore. Campbell et al. hypothesize a global meridional daytime TOA CRF gradient that begins as positive at the equator (2.20–2.59 W·m−2 over land and from −0.46 to 0.42 W·m−2 over ocean at Singapore), becomes neutral in the midlatitudes (0.03–0.27 W·m−2 over land in Maryland), and turns negative moving poleward. This study does not completely confirm Campbell et al., as values are not found as exclusively negative. Evidence in historical reanalysis data suggests that daytime cirrus forcing in and around the subarctic likely once was exclusively negative. Increasing tropopause heights, inducing higher and colder cirrus, have likely increased regional forcing over the last 40 years. We hypothesize that subarctic interannual cloud variability is likely a considerable influence on global cirrus cloud forcing sensitivity, given the irregularity of polar versus midlatitude synoptic weather intrusions. This study and hypothesis lay the basis for an extrapolation of these MPLNET experiments to satellite-based lidar cirrus cloud datasets.
