PUBLICATIONS Journal of Advances in Modeling Earth Systems RESEARCH ARTICLE 10.1002/2013MS000277 Key Points: All three schemes improved the (sub)tropical oceanic boundary layer clouds Differences amongst schemes less than differences to satellite observations Advective component of Dual Mass Flux improves representation of shallow cumulus
Correspondence to: C. C. W. Nam,
[email protected]
Citation: Nam, C. C. W., J. Quaas, R. Neggers, C. Siegenthaler-Le Drian, and F. Isotta (2014), Evaluation of boundary layer cloud parameterizations in the ECHAM5 general circulation model using CALIPSO and CloudSat satellite data, J. Adv. Model. Earth Syst., 6, 300– 314, doi:10.1002/2013MS000277. Received 17 OCT 2013 Accepted 26 FEB 2014 Accepted article online 3 MAR 2014 Published online 2 MAY 2014
Evaluation of boundary layer cloud parameterizations in the ECHAM5 general circulation model using CALIPSO and CloudSat satellite data Christine C. W. Nam1,2, Johannes Quaas1,2, Roel Neggers3, Colombe Siegenthaler-Le Drian4, and Francesco Isotta4,5 1
Max Planck Institute for Meteorology, Hamburg, Germany, 2Leipzig Institute for Meteorology, Universit€at Leipzig, Leipzig, Germany, 3Faculty of Mathematics and Natural Sciences, University of Cologne, Cologne, Germany, 4Swiss Federal Institute of Technology (ETHZ), Zurich, Switzerland, 5Now at MeteoSwiss, Zurich, Switzerland
Abstract Three different boundary layer cloud models are incorporated into the ECHAM5 general circulation model (GCM) and compared to CloudSat and CALIPSO satellite observations. The first boundary layer model builds upon the standard Tiedtke (1989) parameterization for shallow convection with an adapted convective trigger; the second is a bulk parameterization of the effects of transient shallow cumulus clouds; and lastly the Dual Mass Flux (DMF) scheme adjusted to better represent shallow convection. The three schemes improved (Sub)Tropical oceanic low-level cloud cover, however, the fraction of low-level cloud cover remains underestimated compared to CALIPSO observations. The representation of precipitation was improved by all schemes as they reduced the frequency of light intensity events 215 dBZe) at high and midlevels compared to the ECHAM5_Std model. This is not as evident over the Hawaiian region. It should be noted that in the lowest level, frequency of precipitation with reflectivities > 0 dBZe decreased, however, the likelihood of detecting low-level nonprecipitating clouds with the radar simulator did not increase. In fact, fewer low-level clouds in the nonprecipitating part of the histogram are detected in ECHAM5_Trig than ECHAM5_Std even though more low-level clouds modeled in each region (Figure 5). It is likely, the abundance of higher-lying clouds and precipitating hydrometeors obscured the reflectivities from the lowclouds [Nam and Quaas, 2012], particularly since the low-level clouds produced purely by the models rarely develop above 1 km. It is possible, though less likely, that the radar simulator does not detect the newly formed clouds because of a slight underestimate in the effective radius of cloud liquid water as in ECHAM5_Std [Nam and Quaas, 2012]. As with ECHAM5_Trig, the ECHAM5_VSMF shows a greater frequency of high-level ice clouds and precipitation compared to ECHAM5_Std in the Californian stratocumulus and Hawaiian shallow cumulus regions (Figures 4d and 4h). In these plots, the increased frequency of midlevel precipitating hydrometeors are consistent with the increased the frequency of midlevel convection in the Tropics which was found by Isotta et al. [2011]. The increase in convection events provides both more moisture to the upper atmosphere for precipitation in addition to larger particles and higher reflectivities. In regards to the lowest layers of the atmosphere, the ECHAM5_VSMF shows a significant increase in precipitation frequency, which is due to the incorporation of the life cycle of shallow cumulus clouds. Abrupt
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detrainment at the end of the shallow cumulus life cycle provides large amounts of moisture for precipitation in the low-levels of the atmosphere. This is also likely the cause of a break in the precipitation reflectivities around 2 km. Despite the increase in frequency of precipitation, ECHAM5_VSMF also shows an increase in the frequency nonprecipitating boundary layer clouds in the Californian stratocumulus region. The same holds true for the Hawaiian shallow cumulus region. The ECHAM5_DMF, unlike the previous two schemes, shows a decrease in the frequency of high-level clouds and precipitation. In the Californian stratocumulus region, the development of nonprecipitating boundary layer clouds is not evident as the peak in reflectivities remains in the precipitating half of the histogram, obscuring the clouds. There is, however, a slight shift toward lower radar reflectivities. In the Hawaiian shallow cumulus region, the most prominent feature is the increase of low-reflectivity hydrometeors in the lowest levels, particularly in the nonprecipitating region of the histogram. This is due to the advective component of the double PDF which represents cumuliform clouds in conditionally unstable layers. Though the ECHAM5_DMF strongly overestimates the frequency of precipitation at the lowest levels, it is the scheme which best succeeds at substantially increasing the frequency of nonprecipitating boundary layer clouds.
6. Changes in Precipitation ECHAM5_Std has been found to capture the zonal and global distribution pattern of accumulated surface precipitation well compared to observations [Hagemann et al., 2006], however, as with many GCMs it underestimates the contribution and frequency of heavy (>20 mm d21) precipitation and overestimate light ( 0.1, > 1, and > 10 mm d21 were withheld. Precipitating rain with intensities < 0.01 mm d21 yielded radar reflectivities >15 dBZe and rather surprisingly, all other experiments yielded identical radar reflectivity histograms as the
