Breakout Summary Report
ARM/ASR User and PI Meeting
2 - 6 May 2016
Eastern North Atlantic: combining modeling and observations
2 May 2016
1:00 PM - 3:00 PM
0
Robert Wood, Mark Miller
2 May 2016
1:00 PM - 3:00 PM
0
Robert Wood, Mark Miller
Breakout Description
The purpose of the breakout is to share and discuss observational and modeling work focusing on the Eastern North Atlantic (ENA) site, to identify needs for data products and field experiments, and to discuss how to make the best use of ENA data in combination with modeling to address key ASR science goals for warm, low clouds. ARM/ASR have make major investment in the fixed ENA site, including investment in upcoming field experiments. As more ASR investigators begin to use ENA data in their research, there is an important need to coordinate and focus this work to ensure that it most effectively meets ASR science goals. This session strives to serve as a means to aid this coordination.Main Discussion
Discussion focused primarily on responding to science findings raised by individual speakers. Discussion identified the need for state-of-the-art new precipitation retrieval methods to be made available as PI products.Key Findings
Xue Zheng [LLNL] has used CAP-MBL data (all 19 months) from Graciosa to compare against CAM 5 and CAM-CLUBB simulations run in forecast mode. CAM-CLUBB showed some promising improvements over CAM-5 in the representation of cloud cover and cloud variability, and the scaling between cloud cover and liquid water path.Peng Wu [University of North Dakota] examined the formation of drizzle using observations from Graciosa during CAP-MBL. The authors found a relationship between strong drizzle production and vertical wind shear, and hypothesized that in some cases, shear may be enhancing the production of TKE that helps to promote drizzle formation.
Richard Forbes [ECMWF] showed how the ECMWF model systematically overestimates the frequency of light precipitation at Graciosa in every season. The data have been used to improve the ECMWF single-column model by improving the balance of autoconversion, accretion, and evaporation. Forbes and Zheng both identified a desire for quantitative drizzle rate estimates spanning the entire deployment. These would complement the precipitation frequency estimates.
Several years ago, Ewan O’Connor did run his drizzle retrieval for the entire CAP-MBL deployment, but some scientists had noted that these retrievals produced mean drizzle rates at cloud base that were significantly lower than those estimated using spaceborne remote sensing from CloudSat, and there was skepticism that these rates were reliable. Indeed, recent work by Ed Luke and Pavlos Kollias has identified a sizeable bias in the radar reflectivity values from the WACR during that deployment (approximately an 8 dBZ underestimate). Thus, the O’Connor retrieval would need to be re-run.
Jianjun Liu [University of Maryland] and others have examined correlations between cloud microphysical and macrophysical properties and CN concentrations using the CAP-MBL record. They found that retrieved cloud droplet concentration increases with CN concentration, but that LWP decreases slightly, so that the cloud optical thickness increases quite weakly with CN. The authors examined mean values of local meteorological variables for high and low CN cases, but did not find strong meteorological correlation.
Rob Wood [University of Washington] has examined very low CCN events (~factor of 5-10 lower than median concentrations) at Graciosa during CAP-MBL, with a view to trying to understand the meteorological and cloud conditions that may be responsible for the aerosol during these highly depleted events. Conditions 2-3 days upstream of Graciosa may be more important than local processes for causing CCN depletion events.
Jian Wang [BNL] gave an overview of the upcoming ACE-ENA G-1 aircraft deployments to the Azores (Jun-Jul 2017, Jan-Feb 2018) to make measurements of clouds and aerosols in order to improve understanding of aerosol-cloud-precipitation interactions, and provide in situ data for the evaluation of surface-based cloud, precipitation, and aerosol remote sensing. A breakout session later in the week was dedicated to further discussion of ACE-ENA.
Richard Moore [NASA Langley] gave a brief overview of the The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES), an interdisciplinary investigation resolving key processes controlling marine ecosystems and aerosols that are essential to our understanding of Earth system function and future change. NAAMES is funded by the NASA Earth Venture Suborbital Program. NAAMES aims to better understand the connection between ocean ecosystems and aerosols over the North Atlantic. The combined ship and airborne sampling (four deployments during different seasons) is located upstream of Graciosa Island and so is relevant for understanding aerosol-cloud-meteorological connections upstream.