Breakout Summary Report

ARM/ASR User and PI Meeting

13 - 17 March 2017

Session Title: ACPC-Motivated Houston Field Campaign Discussion
Session Date: 13 March 2017
Session Time: 4:00 PM - 6:00 PM
Number of Attendees: 30
Summary Authors: Ann Fridlind, Sue van den Heever

Breakout Description

Goals: Meetings of the Aerosol-Cloud-Precipitation-Climate initative of iLEAPS led to a pilot study of isolated updraft evolution under varying aerosol conditions in the Houston region, where regional pollution sources provide an aerosol perturbation and dynamic susceptibility to aerosol loading is relatively great. Two studies of isolated updraft cell tracking using independent analyses of NEXRAD polarimetric radar data and NU-WRF simulations are motivating consideration of a multi-wavelength polarimetric radar field experiment within the Houston region covered by NEXRAD and Lightning Mapping Array measurements.

Relevance: ARM mobile scanning radars and aerosol measurement resources could serve as the basis for a remote-sensing field campaign in the Houston region. Development of such ideas will be aided by open discussion across the ARM and ASR community at this early stage of potential field campaign project development.

Main Discussion

The breakout session began with an overview of the Aerosol-Cloud-Precipitation-Climate initiative of iLEAPS (and also supported by GEWEX and IGAC). The group's recent history was summarized and its current focus on two project areas outlined: (i) shallow clouds, and (ii) deep convection. The latter was the sole focus of this breakout.

In brief, during meetings at NASA GISS in spring 2015 and at Oxford in spring 2016, the group increasingly identified the unique value of scanning polarimetric radar data to investigate the potential role of aerosol in altering deep convection in nature and in simulations that are used as a basis for climate model parameterizations. Uncertainty in both high- and low-resolution simulations remains high because of the severe sparsity of direct observations, especially within continental updrafts. Given the fact that aircraft data are difficult and dangerous to obtain, and of limited coverage, polarimetric radars are considered a source of information that should be more vigorously mined without delay in order to advance knowledge and confident parameterization of updraft microphysics.

Presenters showed various modelling and observational pilot study components focused on Houston that have been incubated in the ACPC group, including cell-tracking analysis of NEXRAD observations and polarimetric fields estimated from NU-WRF simulations and colocated Lightning Mapping Array data in the observational tracking in two studies (Ryzhkov/Rosenfeld, van Lier Walqui/Fridlind). Idealized simulations and WRF simulations and associated forward calculations from HUCM bin microphysics were also presented (Snyder, Fan), as well as specifications for an international model intercomparison study (van den Heever). Results of aircraft measurement of aerosol in the Houston region were reviewed (Feingold). Forward calculations from Houston NU-WRF simulations were also used to investigate capability of C- and X-band scanning radars to further the scientific objectives (Oue/Kollias). These results from ACPC contributors and others demonstrate the growing impetus towards the scientific exploitation of a Houston-focused analysis of polarimetric radar observations of sea breeze cloud regimes in the air masses that are polluted by crossing over Houston and the neighboring unpolluted air masses serving as control volumes.

Discussion was solicited regarding several general issues. First, is a proposed field campaign to Houston on this topic a good idea and is the general approach of using scanning polarimetric radar sound? Second, what are the resources (DOE ARM, NSF, or otherwise) that could be brought to bear? Third, a slide contributed by Adam Varble was dedicated to considering the barriers to rapid fine-volume scanning using DOE ARM C- and X-band radars, primarily related to resource allocation and how to insure that scanning capability is available for a proposal such as ACPC's to go forward with DOE ARM resources.

Key Findings

There is broad support for a field campaign in the Houston region to investigate isolated updrafts using C- and/or X-band in addition to operational NEXRAD and Lightning Mapping Array observations.

Issues

Certain barriers stand in the way of what ACPC wants to propose now, of which members of the group were not aware prior to Adam Varble's slide contribution. Namely, some had the impression that ACPC could simply request whatever ARM has to offer in the way of rapid-scanning cell-tracking capability, and were unaware that a dedicated spin-up appears to be required in order to be able to request this capability. Much of the discussion time was dedicated to discussing what the barriers are and whether/how they can be surmounted.

Needs

The ACPC strategy uses two measurement approaches that to our knowledge ARM has not deployed thus far but that ARM has unique resources to accomplish: (i) a ground-based CCN+CN measurement network (at least two stations in the polluted and unpolluted sectors, ideally more that allow to assess gradients) and (ii) a multi-wavelength, cell-tracking, rapid-scan approach to obtain as much information as possible from isolated evolving cells within the aerosol observing network. To our knowledge, not many programs have numerous CCN and CN instruments, as well as scanning radars that may be used for such a purpose, under one roof, so to speak.

Decisions

No specific decisions were made at the session (as this was not the session goal), but scientific consensus was furthered that a minimalist field campaign with a network of at least two ground-based aerosol measurements and scanning polarimetric radar resources would be extremely valuable to forward the science of updraft microphysics if it can be accomplished.

Future Plans

The ACPC scientific steering committee, including co-chairs Johannes Quaas and Danny Rosenfeld, stand ready to support a pre-IOP to establish the capability of scan strategies, if that is what is required. We plan to seek guidance from ARM about how to support this going forward.

Action Items

Breakout chair Fridlind presented short slides to the Aerosol and Convective Processes Working Groups later in the meeting, requesting input on the ground-based CCN and CN network (developed by Fridlind, Feingold, and Nicole Riemer), and presented the ACPC rationale for rapid-scan cell tracking to the convection group. The next action item will be to discuss results at the next ACPC meeting in Bad Honnef, Germany, 3–6 April 2017. Following that, we will seek guidance re. support for a possible 'pre-IOP' that could make our proposed plan clearly feasible (see Future Plans).