Papers by Paquita Zuidema
DMW - Deutsche Medizinische Wochenschrift
Bulletin of the American Meteorological Society, 2007
Remote Sensing of Environment, 2007
During the ship-based portion of VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study, VAMOS = Variabi... more During the ship-based portion of VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study, VAMOS = Variability of the American Monsoon Systems) in October and November 2008, NOAA's High Resolution Doppler lidar (HRDL) was used to make lower-trophospheric measurements of horizontal and vertical winds, and uncalibrated lidar backscatter. These data have been processed into profiles of horizontal mean wind, horizontal and vertical velocity variance, and vertical skewness. These profiles were then used to estimate surface-based mixing heights. We present examples of all these observations and introduce a new approach to studying atmospheric decoupling that uses the sub-cloud wind and backscatter measurements to characterize the transport of surface moisture to the cloud level. Average diurnal cycles of mixing height, decoupling, liquid water path, and in-situ measured chemical tracers are presented for two different synoptic regimes encountered during the VOCALS experiment and for different...
Journal of the Meteorological Society of Japan, 2008
... et al. 2004) field experiment in September, 2001. The same cloud radar used duringJASMINE was... more ... et al. 2004) field experiment in September, 2001. The same cloud radar used duringJASMINE was sited at 10°N, 95°W as part of EPIC. Both the ... Pacific (Fig. 4c). JASMINE and EPIC cloud amounts were approximately similar. A low ...
Journal of the Atmospheric Sciences, 2012
Journal of the Atmospheric Sciences, 2012
... Alexander Avramov, Agnieszka Mrowiec, Hugh Morrison, Paquita Zuidema, Matthew D. Shupe, 2012:... more ... Alexander Avramov, Agnieszka Mrowiec, Hugh Morrison, Paquita Zuidema, Matthew D. Shupe, 2012: A FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate Limitations on Rapid Primary Ice Nucleation Processes. J. Atmos. ...
Journal of the Atmospheric Sciences, 2005
The new double-moment microphysics scheme described in Part I of this paper is implemented into a... more 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.
Journal of the Atmospheric Sciences, 2005
The microphysical characteristics, radiative impact, and life cycle of a long-lived, surface-base... more The microphysical characteristics, radiative impact, and life cycle of a long-lived, surface-based mixedlayer, mixed-phase cloud with an average temperature of approximately Ϫ20°C are presented and discussed. The cloud was observed during the Surface Heat Budget of the Arctic experiment (SHEBA) from 1 to 10 May 1998. Vertically resolved properties of the liquid and ice phases are retrieved using surfacebased remote sensors, utilize the adiabatic assumption for the liquid component, and are aided by and validated with aircraft measurements from 4 and 7 May. The cloud radar ice microphysical retrievals, originally developed for all-ice clouds, compare well with aircraft measurements despite the presence of much greater liquid water contents than ice water contents. The retrieved time-mean liquid cloud optical depth of 10.1 Ϯ 7.8 far surpasses the mean ice cloud optical depth of 0.2, so that the liquid phase is primarily responsible for the cloud's radiative (flux) impact. The ice phase, in turn, regulates the overall cloud optical depth through two mechanisms: sedimentation from a thin upper ice cloud, and a local ice production mechanism with a time scale of a few hours, thought to reflect a preferred freezing of the larger liquid drops. The liquid water paths replenish within half a day or less after their uptake by ice, attesting to strong water vapor fluxes. Deeper boundary layer depths and higher cloud optical depths coincide with large-scale rising motion at 850 hPa, but the synoptic activity is also associated with upper-level ice clouds. Interestingly, the local ice formation mechanism appears to be more active when the large-scale subsidence rate implies increased cloud-top entrainment. Strong cloud-top radiative cooling rates promote cloud longevity when the cloud is optically thick. The radiative impact of the cloud upon the surface is significant: a time-mean positive net cloud forcing of 41 W m Ϫ2 with a diurnal amplitude of ϳ20 W m Ϫ2 . This is primarily because a high surface reflectance (0.86) reduces the solar cooling influence. The net cloud forcing is primarily sensitive to cloud optical depth for the low-optical-depth cloudy columns and to the surface reflectance for the high-optical-depth cloudy columns. Any projected increase in the springtime cloud optical depth at this location (76°N, 165°W) is not expected to significantly alter the surface radiation budget, because clouds were almost always present, and almost 60% of the cloudy columns had optical depths Ͼ6.
Journal of the Atmospheric Sciences, 2014
ABSTRACT
Journal of the Atmospheric Sciences, 2008
The net shortwave radiative impact of aerosol on simulations of two shallow marine cloud cases is... more The net shortwave radiative impact of aerosol on simulations of two shallow marine cloud cases is investigated using a Monte Carlo radiative transfer model. For a shallow cumulus case, increased aerosol concentrations are associated not only with smaller droplet sizes but also reduced cloud fractions and cloud dimensions, a result of evaporation-induced mixing and a lack of precipitation. Three-dimensional radiative transfer (3DRT) effects alter the fluxes by 10%-20% from values calculated using the independent column approximation for these simulations. The first (Twomey) aerosol indirect effect is dominant but the decreased cloud fraction reduces the magnitude of the shortwave cloud forcing substantially. The 3DRT effects slightly decrease the sensitivity of the cloud albedo to changes in droplet size under an overhead sun for the two ranges of cloud liquid water paths examined, but not strongly so. A popular two-stream radiative transfer approximation to the cloud susceptibility overestimates the more directly calculated values for the low liquid-water-path clouds within pristine aerosol conditions by a factor of 2 despite performing well otherwise, suggesting caution in its application to the cloud albedos within broken cloud fields. An evaluation of the influence of cloud susceptibility and cloud fraction changes to a "domain" area-weighted cloud susceptibility found that the domain cloud albedo is more likely to increase under aerosol loading at intermediate aerosol concentrations than under the most pristine conditions, contrary to traditional expectations.
Journal of Geophysical Research: Atmospheres, 2011
... retrievals over the Southeast Pacific with VOCALS-REx in situ measurements David Painemal1,2 ... more ... retrievals over the Southeast Pacific with VOCALS-REx in situ measurements David Painemal1,2 and Paquita Zuidema1 Received 26 April 2011; revised 28 October 2011; accepted 28 October 2011; published 30 December 2011. ...
Journal of Geophysical Research, 2003
1] Monte Carlo reflectance simulations of three tropical cumulus congestus clouds reconstructed f... more 1] Monte Carlo reflectance simulations of three tropical cumulus congestus clouds reconstructed from Multiangle Imaging Spectroradiometer (MISR) data are compared to the domain-averaged MISR reflectance measurements. The goal of the comparison is to evaluate the nadir-view pixel cloud optical depth retrievals derived using plane-parallel radiative transfer theory, and the assumptions for vertically distributing the optical depth. Cloud heights are operationally retrieved using a stereo-imaging algorithm. The cloud heights and optical depths are at a 275 m spatial resolution, and for most simulations a vertical resolution of 250 m is applied. Five different but common three-dimensional cloud representations are assessed, using (1) a column vertical-mean volume extinction coefficient (b) value (the reference case), (2) a volume extinction coefficient proportional to the two-thirds power of height (the adiabatic assumption), (3) the adiabatic assumption at a 25 m vertical resolution, (4) a vertical-mean b retrieved from reflectances averaged over a (2.2 km) 2 area, and (5) a vertical-mean b retrieved using off-nadir reflectances. An asymmetry about nadir in the observed reflectance means and skewnesses is not reproduced by any Monte Carlo simulation. The lack of symmetry can be related to differing proportions of unobscured sunlit and shadowed cloudy areas within the different views, even for these cases with viewing angles close to the perpendicular plane. The Monte Carlo simulations do not appear to capture the observed fraction of unobscured sunlit and shadowed cloudy areas, suggesting that radiatively significant cloud variability is occurring at scales smaller than the height field resolution of ±550 m. Results from the Monte Carlo simulation done at a higher vertical resolution are consistent with this. The cases examined also contain a nadir maximum in the observed reflectance skewnesses and a relative maximum for the observed nadir reflectances, attributed to the solar illumination of some optically thick cloud surfaces and to specular reflection pervading through the optically thin cloudy regions. This contrasts with previous modeling results that assume a Lambertian surface.
Journal of Climate, 2009
... Chris Fairall ... a. Datasets Individual ship cruise dates, rawindsonde information, and refe... more ... Chris Fairall ... a. Datasets Individual ship cruise dates, rawindsonde information, and references are given in Table 1. The almost-annual cruises were motivated by the tending of a buoy at 20°S, 85°W, which typically occupied 67 days of each cruise. ...
Journal of Climate, 2006
Cloud radar observations of eastern Pacific intertropical convergence zone cloud vertical structu... more Cloud radar observations of eastern Pacific intertropical convergence zone cloud vertical structure are interpreted in light of soundings, 100-km-scale divergence profiles calculated from precipitation radar Doppler velocities, and surface rain gauge data, from a ship at 10°N, 95°W during the 2001 East Pacific Investigation of Climate (EPIC) experiment. The transition from convective to stratiform rain is clear in all four datasets, indicating a coherence from local to 100-km scale. A novel finding is dry air intrusions at altitudes of 6-8 km, often undercutting upper-level ice clouds. Two distinct dry air source regions are identified. One is a relatively dry area overlying the cooler waters of the Costa Rica oceanic thermocline dome, centered approximately 400 km east-northeast of the ship site. The other is the even drier nearequatorial subsidence zone south of 6°-7°N. The former source is somewhat peculiar to this specific ship location, so that the ship sample is not entirely representative of the region.
Journal of Climate, 2007
Surface flux, wind profiler, oceanic temperature and salinity, and atmospheric moisture, cloud, a... more Surface flux, wind profiler, oceanic temperature and salinity, and atmospheric moisture, cloud, and wind observations gathered from the R/V Altair during the North American Monsoon Experiment (NAME) are presented. The vessel was positioned at the mouth of the Gulf of California halfway between La Paz and Mazatlan (ϳ23.5°N, 108°W), from 7 July to 11 August 2004, with a break from 22 to 27 July. Experimentmean findings include a net heat input from the atmosphere into the ocean of 70 W m Ϫ2 . The dominant cooling was an experiment-mean latent heat flux of 108 W m Ϫ2 , equivalent to an evaporation rate of 0.16 mm h Ϫ1 . Total accumulated rainfall amounted to 42 mm. The oceanic mixed layer had a depth of approximately 20 m and both warmed and freshened during the experiment, despite a dominance of evaporation over local precipitation. The mean atmospheric boundary layer depth was approximately 410 m, deepening with time from an initial value of 350 m. The mean near-surface relative humidity was 66%, increasing to 73% at the top of the boundary layer. The rawinsondes documented an additional moist layer between 2and 3-km altitude associated with a land-sea breeze, and a broad moist layer at 5-6 km associated with land-based convective outflow. The observational period included a strong gulf surge around 13 July associated with the onset of the summer monsoon in southern Arizona. During this surge, mean 1000-700-hPa winds reached 12 m s Ϫ1 , net surface fluxes approached zero, and the atmosphere moistened significantly but little rainfall occurred. The experiment-mean wind diurnal cycle was dominated by mainland Mexico and consisted of a near-surface westerly sea breeze along with two easterly return flows, one at 2-3 km and another at 5-6 km. Each of these altitudes experienced nighttime cloudiness. The corresponding modulation of the radiative cloud forcing diurnal cycle provided a slight positive feedback upon the sea surface temperature. Two findings were notable. One was an advective warming of over 1°C in the oceanic mixed layer temperature associated with the 13 July surge. The second was the high nighttime cloud cover fraction at 5-6 km, dissipating during the day. These clouds appeared to be thin, stratiform, slightly supercooled liquid-phase clouds. The preference for the liquid phase increases the likelihood that the clouds can be advected farther from their source and thereby contribute to a higher-altitude horizontal moisture flux into the United States. 1 The other research boats were the R/V Francisco de Ulloa, which conducted oceanic transects across the mouth of the gulf in June and August, and the R/V Puma, which gathered atmospheric measurements
Journal of Climate, 2010
A new dataset synthesizes in situ and remote sensing observations from research ships deployed to... more A new dataset synthesizes in situ and remote sensing observations from research ships deployed to the southeastern tropical Pacific stratocumulus region for 7 years in boreal fall. Surface meteorology, turbulent and radiative fluxes, aerosols, cloud properties, and rawinsonde profiles were measured on nine ship transects along 208S from 758 to 858W. Fluxes at the ocean surface are essential to the equilibrium SST. Solar radiation is the only warming net heat flux, with 180-200 W m 22 in boreal fall. The strongest cooling is evaporation (60-100 W m 22 ), followed by net thermal infrared radiation (30 W m 22 ) and sensible heat flux (,10 W m 22 ). The 70 W m 22 imbalance of heating at the surface reflects the seasonal SST tendency and some 30 W m 22 cooling that is mostly due to ocean transport.
Journal of Climate, 2012
Widespread stratocumulus clouds were observed on nine transects from seven research cruises to th... more Widespread stratocumulus clouds were observed on nine transects from seven research cruises to the southeastern tropical Pacific Ocean along 208S, 758-858W in October-November of 2001-08. The nine transects sample a unique combination of synoptic and interannual variability affecting the clouds; their ensemble diagnoses longitude-vertical sections of the atmosphere, diurnal cycles of cloud properties and drizzle statistics, and the effect of stratocumulus clouds on surface radiation. Mean cloud fraction was 0.88, and 67% of 10-min overhead cloud fraction observations were overcast. Clouds cleared in the afternoon [1500 local time (LT)] to a minimum of fraction of 0.7. Precipitation radar found strong drizzle with reflectivity above 40 dBZ.
Journal of Applied Meteorology and Climatology, 2010
ABSTRACT Stratocumulus cloud cover patterns and their relationship to drizzle were characterized ... more ABSTRACT Stratocumulus cloud cover patterns and their relationship to drizzle were characterized at San Felix Island (SFI: 26.5°S, 80°W) in the Southeast Pacific. Small closed, large closed and open cells were identified in about 65% of the MODIS (Moderate Resolution Imaging Spectro-radiometer) satellite images during 2003. The MODIS imagery was combined with ceilometer and surface meteorological measurements, human observations of cloud types and drizzle, and large-scale meteorological analyses for January through June. We identified two drizzle regimes: a synoptically-quiescent summer (Jan-March) regime characterized by a strong anticyclone, large closed cells, and frequent drizzle, and an autumn (April-June) regime characterized by a weaker anticyclone, small closed cells and open cells, and precipitation that was mainly associated with synoptic activity. The large closed cells had higher mean cloud bases and tops than the small closed cells, accounted for 45% of the cumulus-under- stratocumulus reports, and 29% of the total drizzle and rain reports. Large closed cells occupied more intermittently-coupled boundary layers than did the small closed cells. Open cells also occurred in more decoupled conditions, but only accounted for 18% of the total reports of drizzle and rain. The atmospheric stability of large and small closed cells were similar, but large closed cells were more commonly associated with a strong anticyclone, and small closed cells with wave activity superimposed upon a weakened anticyclone. The increased drizzle and occurrence of cumulus-under-stratocumulus in the summer rather than autumn is consistent with higher nighttime liquid water paths. A contribution of this study is the documentation of the ways in which synoptic activity can affect stratocumulus decks.
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Papers by Paquita Zuidema