NUMERICAL SIMULATIONS AND DIAGNOSTIC STUDIES
OF METEOROLOGICAL CONDITIONS DURING PEM-TROPICS B
Henry E. Fuelberg
Department of Meteorology
Florida State University
Tallahassee, FL 32306-4520
Research will be conducted in the following areas:
a. Origins and Paths of Air Parcels
We will perform a detailed trajectory analysis to investigate source regions and paths for air parcels encountered during the PEM-Tropics B missions. Global meteorological analyses prepared either by NCEP or ECMWF will serve as input to our kinematic trajectory model. These data are at intervals of 6 or 12 h and horizontal spacings of 1 or 2.5 deg lat/lon, depending on the data source. This research task will consist of several phases.
Trajectory Climatology. We will begin part of the trajectory analysis immediately upon funding. Specifically, we will prepare a backward trajectory climatology for the PEM-Tropics B area and period using data from the previous 10 years. We will prepare trajectories on a daily basis during the various years to sample a wide variety of flow regimes. Trajectories will arrive at the locations and altitudes that might be sampled by the potential DC-8 and P-3B flights. Results will be given to the Science Team for use in advance flight planning. This year by year climatology also will allow us to determine whether the transport that actually occurs during PEM-Tropics B (described later) is climatologically representative. The proposed trajectory climatology will be compared with that prepared for PEM-Tropics A.
Real Time Trajectory Calculations Once the field phase begins, backward trajectories will be very useful in flight planning. We will calculate real time backward trajectories arriving at locations along the possible DC-8 and P-3B flight tracks that are being considered on a given day. These trajectories will be valid on the days of the flights, and will be based on a combination of observed and forecast global data from either NCEP or ECMWF. A cluster approach will be used. Results will be transferred to the aircraft base sites using the best communications available. This procedure will be similar to what we provided during PEM-Tropics A.
Relate Flight Level Chemical Measurements to Origins of the Air. After the PEM-Tropics B field phase is completed, we will determine the histories of air parcels encountered along the various DC-8 and P-3B flight tracks. Specifically, we will select numerous points along the various flight tracks and calculate backward trajectories from these points. Unlike the real time trajectory calculations described above, these post mission trajectories will be based on actual (not proposed) aircraft positions and will utilize only observed meteorological data (i.e., no forecast data). All trajectory data will be provided to the Science Team in a convenient format.
For each trajectory arrival location, we will determine whether the parcel 1) had a stratospheric history, 2) passed over a major land mass where surface chemical sources might be important, or 3) encountered deep convection where lightning was occurring. Our objective is to relate fluctuations in chemical measurements along the flight tracks to the histories of air parcels. We envision close collaboration with the Science Team on this task. For example, the availability of the Harvard University merged chemical data set would greatly facilitate this research.
Compare PEM-Tropics B to Previous Years. We will determine how flow patterns during the PEM-Tropics B field phase compare with those of previous years. This can be done easily by comparing the trajectories calculated for 1999 with those comprising the climatology (both described above). This will be an important step in determining whether conditions encountered during 1999 are representative of most years. This evaluation is especially timely since we have experienced a major El Nino event.
Support the Science Team. Finally, we will provide post-mission trajectory support for all members of the PEM-Tropics B Science Team. Other types of meteorological support will be provided as requested.
b. Detailed Case Studies
Some of the interesting chemical and/or meteorological phenomena that will be observed during PEM-Tropics B should be examined through detailed case studies. For example, layers or plumes of important chemical species or aerosols are likely candidates for study. We will solicit suggestions from the Science Team regarding these post mission case studies. We believe that such a blending of meteorology and atmospheric chemistry will be a valuable component of PEM-Tropics B.
c. Mesoscale Numerical Simulations
We will use the MM5 mesoscale model to perform high resolution studies of atmospheric transport over the PEM-Tropics B domain. This research task will complement the previously described tasks since we will examine small scale transport for a subset of the total flights that are studied at the coarser synoptic scale using global meteorological analyses.
Several PEM-Tropics B flights will be selected for simulation. The Science Team will be consulted in this selection process. Input data to the MM5 model will come from either the NCEP or ECMWF global analyses and from flight level data of the two NASA aircraft. The coarsest MM5 grid scale will be ~100 km, covering the PEM-T domain. Embedded smaller scale grids will be centered over the ITCZ and/or SPCZ. The finest scale grids likely will have a spacing of approximately 10-20 km.
These proposed numerical simulations will provide information at far greater temporal and spatial resolutions than given by global analyses (ECMWF and NCEP). In addition, the MM5’s two-way nesting will permit the mesoscale to interact with the larger synoptic scale. This will be especially important near the ITCZ and SPCZ where widespread deep convection exerts an important influence on its surroundings. Finally, by incorporating flight level meteorological data from the DC-8 and P-3 into the model’s initialization, the proposed simulations will utilize data not used by the global analyses.
The model-generated output will be evaluated against all available conventional data, against observed locations of convection, and against our current knowledge of tropical circulations. Then, the model output will be used to investigate atmospheric transport using high resolution streamlines, trajectories, and/or a passive tracer. The passive tracer will serve as a crude representation of NOx, keeping in mind the lifetime of NOx near the surface and near the tropopause.
We will examine the roles of the ITCZ and SPCZ as barriers to the flow. This will be done at numerous vertical levels. Preliminary results from PEM-Tropics A suggest that these convergence zones are important barriers between the northern and southern hemispheres (ITCZ) and within the South Pacific Basin (SPCZ). Results from these proposed simulations also will be important in understanding measurements from PEM-Tropics A.
We also will examine the vertical transport of air by the widespread deep convection that is associated with the ITCZ and SPCZ. The MM5 will resolve this convection much better than the coarser global analyses (i.e., NCEP or ECMWF).
d. Mission Meteorologist
Prof. Fuelberg will be the DC-8 Mission Meteorologist during PEM-Tropics B. He will be responsible for meteorological forecasting for flight operations and for providing input on the origins and destinations of air parcels encountered during the flights. He will coordinate with other PEM-Tropics meteorologists and seek advice from knowledgeable local meteorologists at the various field sites.
As part of being a Mission Meteorologist, we will prepare meteorological products that will be needed in forecasting and send these products to the field sites. Florida State will prepare backward trajectories that arrive at locations along the proposed flight tracks. We will coordinate the preparation of other meteorological products with Prof. Newell of MIT (the P-3 Mission Meteorologist).