Search Results

You are looking at 1 - 10 of 26 items for

  • Author or Editor: M. Shupe x
  • All content x
Clear All Modify Search
Janet M. Intrieri and Matthew D. Shupe

Abstract

Atmospheric observations from active remote sensors and surface observers, obtained in the western Arctic Ocean between November 1997 and May 1998, were analyzed to determine the physical characteristics and to assess the surface radiative contribution of diamond dust. The observations showed that diamond dust contributed only a negligible radiative effect to the sea ice surface. Surface radiative fluxes and radiative forcing values during diamond dust events were similar in magnitude when compared to observed clear-sky periods. Combined information from lidar, radar, and surface observers showed that diamond dust occurred ∼13% of the time between November and mid-May over the Arctic Ocean and was not observed between mid-May and October. Diamond dust vertical depths, derived from lidar measurements, varied between 100 and 1000 m but were most often observed to be about 250 m.

Lidar and radar measurements were analyzed to assess if precipitation from boundary layer clouds was present during times when surface observers reported diamond dust. This analysis revealed that surface observers had incorrectly coded diamond dust events ∼45% of the time. The miscoded events occurred almost exclusively under conditions with limited or no illumination (December–March). In 95% of the miscoded reports, lidar measurements revealed the presence of thin liquid water clouds precipitating ice crystals down to the surface.

Full access
Matthew D. Shupe and Janet M. Intrieri

Abstract

An annual cycle of cloud and radiation measurements made as part of the Surface Heat Budget of the Arctic (SHEBA) program are utilized to determine which properties of Arctic clouds control the surface radiation balance. Surface cloud radiative forcing (CF), defined as the difference between the all-sky and clear-sky net surface radiative fluxes, was calculated from ground-based measurements of broadband fluxes and results from a clear-sky model. Longwave cloud forcing (CFLW) is shown to be a function of cloud temperature, height, and emissivity (i.e., microphysics). Shortwave cloud forcing (CFSW) is a function of cloud transmittance, surface albedo, and the solar zenith angle. The annual cycle of Arctic CF reveals cloud-induced surface warming through most of the year and a short period of surface cooling in the middle of summer, when cloud shading effects overwhelm cloud greenhouse effects. The sensitivity of CFLW to cloud fraction is about 0.65 W m−2 per percent cloudiness. The sensitivity of CFSW to cloud fraction is a function of insolation and ranges over 0–1.0 W m−2 per percent cloudiness for the sun angles observed at SHEBA. In all seasons, liquid-containing cloud scenes dominate both LW and SW radiative impacts on the surface. The annual mean CFLW (CFSW) for liquid-containing and ice-only cloud scenes is 52 (−21) and 16 (−3) W m−2, respectively. In the LW, 95% of the radiatively important cloud scenes have bases below 4.3 km and have base temperatures warmer than −31°C. The CFLW is particularly sensitive to LWP for LWP < 30 g m−2, which has profound implications in the winter surface radiation balance. The CFSW becomes more negative as surface albedo decreases and at higher sun elevations. Overall, low-level stratiform liquid and mixed-phase clouds are found to be the most important contributors to the Arctic surface radiation balance, while cirrus clouds and diamond dust layers are found to have only a small radiative impact on the Arctic surface.

Full access
D. D. Turner, M. D. Shupe, and A. B. Zwink

Abstract

A 2-yr cloud microphysical property dataset derived from ground-based remote sensors at the Atmospheric Radiation Measurement site near Barrow, Alaska, was used as input into a radiative transfer model to compute radiative heating rate (RHR) profiles in the atmosphere. Both the longwave (LW; 5–100 μm) and shortwave (SW; 0.2–5 μm) RHR profiles show significant month-to-month variability because of seasonal dependence in the vertical profiles of cloud liquid and ice water contents, with additional contributions from the seasonal dependencies of solar zenith angle, water vapor amount, and temperature. The LW and SW RHR profiles were binned to provide characteristic profiles as a function of cloud type and liquid water path (LWP). Single-layer liquid-only clouds are shown to have larger (10–30 K day−1) LW radiative cooling rates at the top of the cloud layer than single-layer mixed-phase clouds; this is due primarily to differences in the vertical distribution of liquid water between the two classes. However, differences in SW RHR profiles at the top of these two classes of clouds are less than 3 K day−1. The absolute value of the RHR in single-layer ice-only clouds is an order of magnitude smaller than in liquid-bearing clouds. Furthermore, for double-layer cloud systems, the phase and condensed water path of the upper cloud strongly modulate the radiative cooling both at the top and within the lower-level cloud. While sensitivity to cloud overlap and phase has been shown previously, the characteristic RHR profiles are markedly different between the different cloud classifications.

Full access
H. Morrison, J. A. Curry, M. D. Shupe, and P. Zuidema

Abstract

The new double-moment microphysics scheme described in Part I of this paper is implemented into a single-column model to simulate clouds and radiation observed during the period 1 April–15 May 1998 of the Surface Heat Budget of the Arctic (SHEBA) and First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment–Arctic Clouds Experiment (FIRE–ACE) field projects. Mean predicted cloud boundaries and total cloud fraction compare reasonably well with observations. Cloud phase partitioning, which is crucial in determining the surface radiative fluxes, is fairly similar to ground-based retrievals. However, the fraction of time that liquid is present in the column is somewhat underpredicted, leading to small biases in the downwelling shortwave and longwave radiative fluxes at the surface. Results using the new scheme are compared to parallel simulations using other microphysics parameterizations of varying complexity. The predicted liquid water path and cloud phase is significantly improved using the new scheme relative to a single-moment parameterization predicting only the mixing ratio of the water species. Results indicate that a realistic treatment of cloud ice number concentration (prognosing rather than diagnosing) is needed to simulate arctic clouds. Sensitivity tests are also performed by varying the aerosol size, solubility, and number concentration to explore potential cloud–aerosol–radiation interactions in arctic stratus.

Full access
J. Verlinde, B. D. Zak, M. D. Shupe, M. D. Ivey, and K. Stamnes
Full access
S. W. Dorsi, M. D. Shupe, P. O. G. Persson, D. E. Kingsmill, and L. M. Avallone

Abstract

Observations from a series of frontal and postfrontal storms during the Colorado Airborne Multiphase Cloud Study (CAMPS) are combined to show transitions in cloud dynamics and microphysical statistics over a mountain range. During 10 flights in 2010 and 2011, along-wind, across-ridge transects over the Colorado Park Range are performed to statistically characterize air motion and microphysical conditions and their variability. Composite transect statistics show median vertical winds to be mostly upward windward of the ridge axis, and that cloud water concentration (CWC) and ice-particle number concentration are greatest near the ridge. Mixed-phase clouds were found throughout the study area, but increase in frequency by 70% relative to other cloud types in the vicinity of the range. Compared to ice-only clouds, mixed-phase clouds are associated with greater near-ridge increases in CWC and preferentially occur in regions with greater vertical wind variability or updrafts. Strong leeside reductions in CWC, the abundance of mixed-phase clouds, and number concentration of ice particles reflect the dominance of precipitation and particle mass loss processes, rather than cloud growth processes, downwind from the topographic barrier. On days in which the air column stability does not support lee subsidence, this spatial configuration is markedly different, with both ice- and liquid-water-bearing clouds appearing near the ridgeline and extending downwind. A case study from 9 January 2011 highlights mixed-phase regions in trapped lee waves, and in a near-ridgetop layer with evidence of low-altitude ice particle growth.

Full access
Matthew D. Shupe, Jennifer M. Comstock, David D. Turner, and Gerald G. Mace
Full access
Matthew D. Shupe, David D. Turner, Alexander Zwink, Mandana M. Thieman, Eli J. Mlawer, and Timothy Shippert

Abstract

Cloud phase and microphysical properties control the radiative effects of clouds in the climate system and are therefore crucial to characterize in a variety of conditions and locations. An Arctic-specific, ground-based, multisensor cloud retrieval system is described here and applied to 2 yr of observations from Barrow, Alaska. Over these 2 yr, clouds occurred 75% of the time, with cloud ice and liquid each occurring nearly 60% of the time. Liquid water occurred at least 25% of the time, even in winter, and existed up to heights of 8 km. The vertically integrated mass of liquid was typically larger than that of ice. While it is generally difficult to evaluate the overall uncertainty of a comprehensive cloud retrieval system of this type, radiative flux closure analyses were performed in which flux calculations using the derived microphysical properties were compared with measurements at the surface and the top of the atmosphere. Radiative closure biases were generally smaller for cloudy scenes relative to clear skies, while the variability of flux closure results was only moderately larger than under clear skies. The best closure at the surface was obtained for liquid-containing clouds. Radiative closure results were compared with those based on a similar, yet simpler, cloud retrieval system. These comparisons demonstrated the importance of accurate cloud-phase and cloud-type classification, and specifically the identification of liquid water, for determining radiative fluxes. Enhanced retrievals of liquid water path for thin clouds were also shown to improve radiative flux calculations.

Full access
Matthew D. Shupe, Pavlos Kollias, P. Ola G. Persson, and Greg M. McFarquhar

Abstract

The characteristics of Arctic mixed-phase stratiform clouds and their relation to vertical air motions are examined using ground-based observations during the Mixed-Phase Arctic Cloud Experiment (MPACE) in Barrow, Alaska, during fall 2004. The cloud macrophysical, microphysical, and dynamical properties are derived from a suite of active and passive remote sensors. Low-level, single-layer, mixed-phase stratiform clouds are typically topped by a 400–700-m-deep liquid water layer from which ice crystals precipitate. These clouds are strongly dominated (85% by mass) by liquid water. On average, an in-cloud updraft of 0.4 m s−1 sustains the clouds, although cloud-scale circulations lead to a variability of up to ±2 m s−1 from the average. Dominant scales-of-variability in both vertical air motions and cloud microphysical properties retrieved by this analysis occur at 0.5–10-km wavelengths. In updrafts, both cloud liquid and ice mass grow, although the net liquid mass growth is usually largest. Between updrafts, nearly all ice falls out and/or sublimates while the cloud liquid diminishes but does not completely evaporate. The persistence of liquid water throughout these cloud cycles suggests that ice-forming nuclei, and thus ice crystal, concentrations must be limited and that water vapor is plentiful. These details are brought together within the context of a conceptual model relating cloud-scale dynamics and microphysics.

Full access
Michael Tjernström, Matthew D. Shupe, Ian M. Brooks, Peggy Achtert, John Prytherch, and Joseph Sedlar

Abstract

During the Arctic Clouds in Summer Experiment (ACSE) in summer 2014 a weeklong period of warm-air advection over melting sea ice, with the formation of a strong surface temperature inversion and dense fog, was observed. Based on an analysis of the surface energy budget, we formulated the hypothesis that, because of the airmass transformation, additional surface heating occurs during warm-air intrusions in a zone near the ice edge. To test this hypothesis, we explore all cases with surface inversions occurring during ACSE and then characterize the inversions in detail. We find that they always occur with advection from the south and are associated with subsidence. Analyzing only inversion cases over sea ice, we find two categories: one with increasing moisture in the inversion and one with constant or decreasing moisture with height. During surface inversions with increasing moisture with height, an extra 10–25 W m−2 of surface heating was observed, compared to cases without surface inversions; the surface turbulent heat flux was the largest single term. Cases with less moisture in the inversion were often cloud free and the extra solar radiation plus the turbulent surface heat flux caused by the inversion was roughly balanced by the loss of net longwave radiation.

Full access