Description of the AMIE-Gan objective analysis of large scale forcing data

The netcdf data have been released as regular ARM data and are now available in the main ARM Archive. Please access the data for the following links for each datastream
gan180varanaecmwfanatrmmX1.c1
gan180varanaecmwfanaadsmartrX1.c1
gan180varanaecmwfanasmartrX1.c1
gan180varanaecmwfanaspolX1.c1

1. Overview

The constrained variational objective analysis approach described in Zhang and Lin 1997 and Zhang et al. 2001 was used to derive the large-scale single-column/cloud resolving model forcing and evaluation data set from the observational data collected during ARM MJO Investigation Experiment (AMIE), which was conducted during October 2011 to March 2012 on Gan Island in the Maldives. The forcing data represent an average over the analysis domain centered at ARM mobile facility with a diameter of 300 km as shown in Figure 1.

Due to the lack of a sounding array at Gan Island, the forcing data for AMIE-Gan was developed based on ECMWF analyses, which were then constrained with observed surface rainfall through the constrained variational objective analysis. Three versions of the forcing data are provided, which were constrained by surface precipitation retrieved from SMART-R, S-POL, and TRMM precipitation radar measurements, respectively, to address uncertainties in surface rainfall. With the ongoing effort to address some calibration issues with the SMART-R and S-POL in the AMIE/DYNAMO radar community, the large-scale forcing data expect to be updated in the near future once the improved radar precipitation data are available. However, we expect that only the magnitude of the forcing fields will be affected, not the timing and the vertical structures.

The data here are in both ASCII and netCDF formats for three domains.

Standard vertical resolution (25mb) data

There are two standard resolution (25mb) ASCII data files for layered variables and surface variables, respectively for each of the domain. They are:

S-POL based forcing (version v0):

gan180varanaecmwfanaspolsurfaceC1.c1.20111113.000000.dat
gan180varanaecmwfanaspollayerC1.c1.20111113.000000.dat

SMART_R based forcing (version v1):

gan180varanaecmwfanasmartrsurfaceC1.c1.20111002.000000.dat
gan180varanaecmwfanasmartrlayerC1.c1.20111002.000000.dat

SMART_R adjusted based forcing (version v1):

gan180varanaecmwfanaadjsmartrsurfaceC1.c1.20111002.000000.dat
gan180varanaecmwfanaadjsmartrlayerC1.c1.20111002.000000.dat

TRMM based forcing (version v1):

gan180varanaecmwfanatrmmsurfaceC1.c1.20111002.000000.dat
gan180varanaecmwfanatrmmlayerC1.c1.20111002.000000.dat

These ASCII data files can be read using following FORTRAN files

read_layer.for
read_surface.for

The netCDF files that include all the variables contained in the two ASCII data files are also provided:


gan180varanaecmwfanaspolC1.c1.20111113.000000.cdf (S-POL based)
gan180varanaecmwfanasmartrC1.c1.20111002.000000.cdf (SMART_R based)
gan180varanaecmwfanaadjsmartrC1.c1.20111002.000000.cdf   (SMART_R adjusted based) gan180varanaecmwfanatrmmC1.c1.20111002.000000.cdf (TRMM based)

To see the quick look plots of the data please go to:

http://www-pcmdi.llnl.gov/ARM/scm-forcing/gan-amie/html/preview_amie.html

 

2. Some details of the analysis

The objective analysis domains used for analyzing the AMIE-GAN data are shown in Figure 1. The domain-averaged surface and TOA radiative fluxes and surface heat fluxes constraints required by the variational analysis were obtained from ECMWF analysis data.

TRMM precipitation data is based on 3B42 data. We use the RATE_ZH for precipitation retrieval from SPOL data. This is just one of many rates that S-Pol is able to calculate, and there is some active discussion going on concerning which rate is the "best" rate to use for the AMIE campaign. Due to a blockage issue, the areal averaged rain rate applies only to about one-third of the S-Pol domain, from about 38 thru 158 degrees, and for a radar range of 17 to 100 km. SMART-R radar retrieved rain rate is also only using the 180 deg sector from 338 to 158 deg because of blockage to the west. If future improvement is made on these retrievals, forcing dataset may change accordingly.

 

3.     Notes on Newly Release of Version 1

In this new release, 

 

 

4.     References

Zhang, M. H., and J. L. Lin (1997), Constrained variational analysis of sounding data bases on column-integrated budgets of mass, heat, moisture, and momentum: Approach and application to ARM measurements., J. Atmos. Sci., 54, 1503-1524.

Zhang, M. H., J. L. Lin, R. T. Cederwall, J. J. Yio, and S. C. Xie (2001), Objective analysis of ARM IOP Data: Method and sensitivity, Mon. Weather Rev., 129, 295-311.

AMIE Homepage: http://campaign.arm.gov/amie/

AMIE forcing data page on LLNL ARM Team page: http://www-pcmdi.llnl.gov/ARM/scm-forcing/gan-amie/html/preview_amie.html

5. Acknowledgement

We would like to thank Bob Rilling, Steve Williams (NCAR), Courtney Schumarcher and Aaron Funk (TAMU), Chuck Long (PNNL) and Chidong Zhang (FSU) and all AMIE participants who collected and provided the valuable field data for this study.

6. Contacts

For questions, or to report data problems, please contact:

Shaocheng Xie: xie2@llnl.gov
Renata McCoy:
mccoy20@llnl.gov
Yunyan Zhang:
zhang25@llnl.gov

 

http://iop.archive.arm.gov/arm-iop-file/0eval-data/xie/scm-forcing/iop_at_gan/image002.gif

Figure 1: Analysis domain for AMIE-Gan, with diameters of 300 km. The red triangles denote sounding locations.

Figure 2: Precipitation Rate for 1st and 2nd MJO.  Notice the double-peak behavior in SMART-R becomes smaller in the adjusted SMART-R precipitation rate.

 

 

 

Figure 3: Omega field based on different precipitation rates from TRMM, SMART-R and adjusted SMART-R during 1st and 2nd MJO periods.