NARE 7 September 1993 case STUDY

Part 3. NARE 7 September 1993. The purpose of Part 3 is to compare model results with observations.  The case chosen is the NARE 7 September 1993 intensive investigation over the Bay of Fundy in the Gulf of Maine.  A description of the meteorology and chemistry for this case can be found here.

Simulation. Observations of stratus cloud and chemical/aerosol constituents were made from the 4-7 September 1993 over the Bay of Fundy.  There is sufficient independent data for initialization and model evaluation.

Two scales of models could be used to simulate this case.  Cloud-scale models can be used to simulate the stratus deck and obtain detailed information on the chemical and aerosol characteristics of the boundary layer.  Regional or large scale models can be used to assess the importance of transported chemical species and aerosols to the region.

We are focusing on the cloud scale, but still encourage regional scale simulations.  If you plan to perform a regional scale simulation, please email barthm@ucar.edu.

Location: approximately 44N, 66W

The sounding is taken from the September 7 radiosonde near Yarmouth, Nova Scotia at 1115 UTC.

The thermodynamic sounding is available in PC or UNIX format.

The original data have been interpolated to a 25 m vertical resolution. If you wish to have the original sounding data, please contact me (barthm@ucar.edu).

The surface fluxes and large-scale subsidence control the growth of the boundary layer. These are some values used in a preliminary simulation. Feel free to adjust these numbers.

Surface fluxes:

Large-scale subsidence:

Initialization of chemical species is based upon two profiles obtained by the NRCC Twin Otter from 1545-1630 and 1640-1650 UTC 7 September 1993.  These measurements, which include O₃, H₂O₂, NO_y, SO₂, and CO, have been binned into 25 m altitude bins to match the heights given above.  The SO₂ and H₂O₂ instruments have a relatively slow response.  The data have been adjusted in a simple way for the lag and response delay of these instruments.  As a consequence, the location of the pollution layers and boundary layer height may not be well-defined by these measurements.  This may lead to some further adjustment of these profiles, especially for the location of the cloud and SO₂  plume.  In addition the covariance of SO₂ and H₂O₂ with other variables may not be great.

The chemistry sounding is available in PC and UNIX format.

Figures of NO_y, SO₂, H₂O₂, O₃, and CO can be viewed HERE.

If you would prefer to obtain the 1 second data, go to the NARE homepage at http://www1.tor.ec.gc.ca/armp/NARE/NARE.html. Click on NARE Flight Data (after scrolling down a bit).  Then after scrolling down about 2/3 of the way, click on NAREflt.45.txt.  This file contains many other meteorological and aerosol variables that may be of use.

For species that are not listed above, do the following:

Set:

If you are not predicting PAN, set HNO₃ = NO_y - NO_x

If you are predicting PAN concentrations, partition NO_z (= NO_y - NO_x) to be 60% HNO3 and 40% PAN.

Set CO₂ = 355. ppmv everywhere.

NH₃ = 100 pptv at the surface; scale with the NO_y profile, but with a maximum NH₃ mixing ratio of 200 pptv.

SO₄^2- is calculated from PCASP channel 7 data during the same profile as the chemical data. The calculation of SO₄^2- from PCASP channel 7 (PC7) is a polynomial fit derived by Richard Leaitch:

SO₄^2- = 3.25e-9 (PC7)⁴ - 2.94e-6 (PC7)³ + 8.01e-4 (PC7)² + 4.45E-03 (PC7)

where SO₄^2- is in units of mg/m³, PC7 per cubic centimeter, and negative values are set to zero. The conversion from mg/m³ to ppbv is:

SO₄^2-(ppbv) = SO₄^2-(mg/m³) * 28.97/96. / rhoair(kg/m³)

In cloud the SO₄^2- in cloud water has been converted to an equivalent amount in air.  This number could be in error due to production of SO₄^2- from aqueous SO₂.

The results are in the sulfate sounding in PC and UNIX format.

If you are simulating hydrocarbons, please see Kleinman et al (1996).

Number, surface and volume size distributions are shown for two heights: below cloud (265 m) and just below cloud base (400 m). In addition, values of liquid water content and droplet number binned into 25 m altitude levels are provided as a function of height. There is much more variation of these variables as seen in the one-second data.

Photolysis rates:

Calculate the rates for (44N, 66W) midday conditions. (Assuming that your cloud-scale integration lasts for just a few hours.). Suggested values:

Model results will be compared with the 1835-2025 UTC  7 September measurements (flight 46 of the Twin Otter).  Please provide the following from the model time that you feel best matches the observations:

For 2-D and 3-D simulations, horizontally average the model results over the model domain to obtain vertical profiles of:

Interstitial values averaged between 740 and 780 m altitude (or provide vertical profiles) for O₃, H₂O₂, SO₂, N_p (interstitial aerosol number), LWC, N_d