GACP Projects
Form A: GACP ACCOMPLISHMENT REPORT
Name: Philip Rasch
Institution: NCAR
TITLE: Travel funds for aerosol research for Rasch and colleagues
ABSTRACT:
I submitted a "letter proposal" fund travel to NASA labs and
related aerosol meetings.
GOALS:
Understanding aerosols interaction with clouds, chemistry and climate.
OBJECTIVES:
We are interested in characterizing the interaction
between aerosols and climate. We are particularly interested in the
direct and indirect radiative forcing by aerosols on the earth's
climate. We wish to be able to attribute region of origin,
chemical composition, and pathways of production and removal to the
different aerosol types.
APPROACH:
We use a general circulation model (NCAR CCM), a related
chemical transport model (MATCH), and observations (currently
satellite, and in-situ measurements) to work toward the above goals
and objectives.
The CCM can be used to study interactions and feedbacks between aerosols and climate in a statistical (climatological) sense. MATCH uses a prescribed meteorological specification to drive the transport, production and removal of aerosols, The two models share many common representations for the processes controlling aerosols. Because of this we can model aerosols and their interations with climate within the GCM, and use nearly identical parameterizations within MATCH to study particular events and compare directly to measurements at a particular time when the meteorological data is taken from a forecast center analysis. The results from these two models can be compared to long term measuements in a statistical sense, or to measurements made at a specific place and time.
We have recently developed a version of MATCH that allows one to assimilate satellite measurements directly into the aerosol model. We term procedure an aerosol assimilation. We describe it in the next section.
Describe the methodology and techniques that you used to accomplish your research objectives.
TASKS COMPLETED:
In view of the fact that the funding was just for travel, I will be
very brief here about our own research, and just mention the main
focal topics of our group, and how the money was spent.
We are currently modeling dust, sea salt, sulfate and carbonaceous aerosols in the CCM and MATCH models (discussed above). My particular interests are in sulfate and carbon aerosols, and their interactions with clouds. We use these models to understand aerosol forcing, and climate response. A series of papers were published describing the sulfur model, characterizing the sources and sinks for atmospheric sulfate, and estimating the direct and indirect radiative forcing associated with aerosols of anthropogenic origin.
We also developed an aerosol assimilation procedure (discussed in more detail below) that is capable of producing a global gridded aerosol climatology that agrees with observations where they are available in space and time, and uses the model to interpolate in space and timer, where observations are lacking. Other papers are in preparation characterizing the aerosol assimilation technique, and the composition, region of origin and controlling processes for the aerosols in the INDOEX region.
The funding provided by NASA was used to:
- attend the first GACP science team meeting at GISS in Sept of 1998.
- attend the IGAC-SUTA/ILIAS coordinating commitee meeting in Hamburg Germany by Rasch and W.C. Collins (the Co-PI on the aerosol assimilation project).
FUTURE PLANS:
Now that the INDOEX field phase is complete, the NCAR C4 group is
planning to produce a gridded aerosol analysis for the INDOEX region
including information on passive-tracer transport and the speciation
of the aerosols. We plan to develop procedures for assimilating in
situ and lidar observations of aerosols as these become available from
the rest of the INDOEX science team. The goals of our investigation
are to compute the extrapolate the INDOEX measurements over the entire
Indian Ocean, compute the large-scale direct radiative forcing of
aerosols, and relate the in situ observations to the large-scale
aerosol distributions. Although our initial application was limited
to the Indian Ocean, our methodology could be extended to derive
global aerosol analyses combining in situ and remotely-sensed aerosol
observations.
We are also actively working with scientists within NASA involved with AVHRR, GLAS and MODIS and AERONET on the utilization of those data to understand the model and to utilize in the assimilation procedure.
RESULTS:
I will defer a discussion of scientific and technical results to the
significant highlights section.
Form B: GACP SIGNIFICANT HIGHLIGHTS
Name: Philip Rasch, William Collins, Brian Eaton
Institution: NCAR
SIGNIFICANT HIGHLIGHTS:
A system for forecasting aerosols has been developed using a chemical
transport model together with an assimilation of satellite aerosol
retrievals. Bill Collins, Phil Rasch, and Brian Eaton of NCAR
implemented the forecast system to help develop aircraft missions
during the Indian Ocean experiment (INDOEX). The forecasting system
consists of the Model of Atmospheric Transport and Chemistry (MATCH)
combined with an assimilation package originally developed for
atmospheric chemistry applications. The aerosols forecast by MATCH
include sulfate, mineral dust, carbonaceous, and sea-salt aerosols.
The model includes a detailed treatment of the sources, chemical
transformation, and wet and dry deposition of the aerosol species.
The aerosol forecasts involve a two-stage process. During the assimilation phase, the total column aerosol optical depth (AOD) is estimated from the model aerosol fields. The model state is then adjusted to minimize differences between the simulated AOD and satellite retrievals of aerosol optical depth. During the subsequent forecast phase, the aerosol fields are evolved using meteorological forecasts. The assimilation package was modified to treat aerosols by the NCAR C4 scientists.
During INDOEX, the NCAR team produced 24 and 48-hour forecasts of the total aerosol optical depth over the Indian Ocean region. The model was integrated using global near-real-time meteorology supplied by NCEP. The meteorological forecast and analysis fields were sampled at 3-hourly intervals at T126 horizontal resolution, approximately 0.8 degrees at the equator. The satellite aerosol retrievals were derived from high-resolution AVHRR data acquired at the INDOEX operations site on Male and from low-resolution AVHRR data supplied by NOAA. The satellite and meteorological data were collected and processed at NCAR and the forecasts were then transmitted back to Male. Bill Collins and Phil Rasch both traveled to Male to interpret the forecasts for the ship and aircraft mission scientists.
We believe this aerosol assimilation procedure is of direct relevance to the goals of GACP. The assimilation procedure provides a novel and effective method for producing a global gridded aerosol climatology that agrees with observations at points where observations are available in space and time, and uses the model to interpolate in space and time where observations are lacking. The model provides additional information about aerosol composition, region of origin, and processes that control formation and removal, that are not directly available from the observations.
More detail about the procedure, products and figures are available on the web at http://www.cgd.ucar.edu/cms/match/
Form C: FUTURE PLANS
Name: Philip Rasch
Institution: NCAR
It is my intention to continue to use the funding for travel for me and my group, and, given the approval of the program managers and my admin. people, possibly for an inexpensive laptop to facilitate work while traveling.
Form D: GACP BIBLIOGRAPHY
Name: Phil Rasch
Institution: NCAR
BIBLIOGRAPHY:
Papers, reports, and presentations refer to those published during
GACP by the principal investigator, co-investigators, and other
researchers supported by your agency for aerosol research. Include
those in progress or planned.
a. List of publications (including books, book chapters, and refereed papers), using AMS bibliographic citation form.
Barth, M., P. J. Rasch, J. T. Kiehl, C. M. Benkovitz, S. E. Schwartz: Sulfur chemistry in the NCAR CCM: Part I; Description, evaluation, features and influence of aqueous chemistry, JGR, 1999, in press.
Collins, W. D, P. J. Rasch, B. E. Eaton, B. Khattatov, J.-F. Lamarque, C. S. Zender: Forecasting aerosols using a Chemical Transport Model with assimilation of satellite aerosol retrievals: Methology for INDOEX, JGR, 2000, in preparation.
Kiehl, J.T, T. L. Schneider, P. J. Rasch, M. Barth, J. Wong: Radiative Forcing due to Sulfate aerosols from simulations with the NCAR Community Climate Model (CCM3), JGR, 1998, in press.
Lawrence, M. J., P. J. Crutzen, P. J. Rasch, B. E. Eaton, N. M. Mahowald: A model for studies of tropospheric photochemistry: 1. Description and GLobal simulation Characteristics, JGR, 1999, accepted.
Rasch, P. J., M. Barth, J. T. Kiehl, A sulfur model for the NCAR CCM: Part II; Description of the atmospheric sulfur cycle. Global budgets, and controlling processes, JGR, 1999, in press.
Rasch, P. J., W. D. Collina, B. E. Eaton: Forecasting aerosols using a Chemical Transport Model with assimilation of satellite aerosol retrievals: Understanding INDOEX aerosol distributions., JGR, 2000, in preparation.
Rasch, P. J., J. Feichter, K. Law, N. Mahowald, J. Penner, C. Benkovitz, C. Genthon, C. Giannakopoulos, P. Kasibhatla, D. Koch, H. Levy, T. Maki, M. Prather, D. L. Roberts, G.-J. Roelofs, D. Stevenson, Z. Stockwell, S. Taguchi, M. Kritz, M. Chipperfield, D. Baldocchi, P. McMurry, L. Barrie, T. Balkanski, R. Chatfield, E. Kjellstrom, M. Lawrence, H. N. Lee, J. Lelieveld, K. J. Noone, J. Seinfeld, G. Stenchikov, S. Schwarz, C. Walcek, D. Williamson: An assessment of scavenging and deposition processes in global models; results from the WCRP Cambridge workshop of 1995, 1999, Tellus, submitted.
b. List of oral presentations or posters at professional society meetings and conferences.
Rasch, P. J., W. D. Collins, B. E. Eaton, Forecasting aerosols using a CTM with assimilation of satellite aerosol retrievals 2. A 4D aerosol analysis for INDOEX, AGU, spring 1999.
Collins, W. D, P. J. Rasch, B. E. Eaton, Forecasting aerosols using a CTM with assimilation of satellite aerosol retrievals 1. Methology for INDOEX, AGU, Spring, 1999.
