Ground altitude for the same point varies with start date/time

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hbarbosa
Posts: 7
Joined: May 18th, 2015, 3:55 pm
Registered HYSPLIT User: No

Ground altitude for the same point varies with start date/time

Post by hbarbosa » September 21st, 2017, 9:45 pm

Dear All,

I'm running many backward trajectories starting at the same lat/lon and altitude above ground but separated in steps of 1h, for all hours in a particular month.

The column before last in my output files (endpoint file format) is named TERR_MSL and, as far as I understand, it should be the terrain altitude in meters above sea level, along the trajectory. Therefore, if I look just in the first line of each output file (i.e. time = 0h backwards) this values should always be the same (ground altitude of start position).

In my output files, however, they vary! See:

t140319_0800_backward.dat.T3
8 PRESSURE THETA AIR_TEMP RAINFALL MIXDEPTH RELHUMID TERR_MSL SUN_FLUX
1 1 14 3 19 8 0 2 0.0 -3.213 -60.598 100.0 995.2 297.9 297.5 0.6 41.4 91.7 62.8 0.0

t140319_0900_backward.dat.T3
8 PRESSURE THETA AIR_TEMP RAINFALL MIXDEPTH RELHUMID TERR_MSL SUN_FLUX
1 1 14 3 19 9 0 3 0.0 -3.213 -60.598 100.0 995.7 297.8 297.4 0.7 39.6 92.6 62.7 0.0

t140319_1000_backward.dat.T3
8 PRESSURE THETA AIR_TEMP RAINFALL MIXDEPTH RELHUMID TERR_MSL SUN_FLUX
1 1 14 3 19 10 0 2 0.0 -3.213 -60.598 100.0 995.7 298.2 297.8 0.0 67.5 89.1 51.0 12.8



How can the initial ground altitude be changing?
Is this expected? or is this a bug?

More information:

Running on a SGI cluster, with linux SLES11
Hysplit4 downloaded in July 2015
Input is GDAS 0.5 degrees


TRAJ.CFG======
&SETUP
tratio = 0.75,
delt = 0.0,
mgmin = 10,
khmax = 9999,
kmixd = 0,
kmsl = 0,
kagl = 1,
k10m = 1,
nstr = 0,
mhrs = 9999,
nver = 0,
tout = 60,
tm_pres = 1,
tm_tpot = 1,
tm_tamb = 1,
tm_rain = 1,
tm_mixd = 1,
tm_relh = 1,
tm_sphu = 0,
tm_mixr = 0,
tm_dswf = 1,
tm_terr = 1,
dxf = 1.00,
dyf = 1.00,
dzf = 0.01,
messg = 'MESSAGE',
/

SETUP======
&SETUP
TM_PRES=1,
TM_TPOT=1,
TM_TAMB=1,
TM_RAIN=1,
TM_MIXD=1,
TM_TERR=1,
TM_DSWF=1,
TM_RELH=1,
TOUT=60,
/

ASCDATA.CFG======
-90.0 -180.0 lat/lon of lower left corner
0.5 0.5 lat/lon spacing in degrees
360 720 lat/lon number of data points
2 default land use category
0.2 default roughness length (m)
'../bdyfiles0p5/' directory of files

CONTROL=====
14 01 01 00 30
6
-3.212972 -60.598056 100
-3.139200 -60.131530 100
-3.097220 -59.986700 100
-2.890476 -59.969899 100
-2.594580 -60.209300 100
-2.144111 -58.999861 100
-336
0
10000.0
17
/work/hbarbosa/gdas0p5/
20140102_gdas0p5
/work/hbarbosa/gdas0p5/
20140101_gdas0p5
/work/hbarbosa/gdas0p5/
20131231_gdas0p5
/work/hbarbosa/gdas0p5/
20131230_gdas0p5
/work/hbarbosa/gdas0p5/
20131229_gdas0p5
/work/hbarbosa/gdas0p5/
20131228_gdas0p5
/work/hbarbosa/gdas0p5/
20131227_gdas0p5
/work/hbarbosa/gdas0p5/
20131226_gdas0p5
/work/hbarbosa/gdas0p5/
20131225_gdas0p5
/work/hbarbosa/gdas0p5/
20131224_gdas0p5
/work/hbarbosa/gdas0p5/
20131223_gdas0p5
/work/hbarbosa/gdas0p5/
20131222_gdas0p5
/work/hbarbosa/gdas0p5/
20131221_gdas0p5
/work/hbarbosa/gdas0p5/
20131220_gdas0p5
/work/hbarbosa/gdas0p5/
20131219_gdas0p5
/work/hbarbosa/gdas0p5/
20131218_gdas0p5
/work/hbarbosa/gdas0p5/
20131217_gdas0p5
/home/hbarbosa/hysplit/goam0p5/backward/
t140101_0030_backward.dat

barbara.stunder
Posts: 218
Joined: November 9th, 2012, 4:23 pm
Registered HYSPLIT User: Yes

Re: Ground altitude for the same point varies with start date/time

Post by barbara.stunder » September 22nd, 2017, 10:26 am

These results are reasonable. Terrain height is calculated from the input meteorology. See also viewtopic.php?t=1155

hbarbosa
Posts: 7
Joined: May 18th, 2015, 3:55 pm
Registered HYSPLIT User: No

Re: Ground altitude for the same point varies with start date/time

Post by hbarbosa » September 22nd, 2017, 8:18 pm

Dear Barbara,

I checked the other post you mentioned, but there is no real explanation, it just says that ground altitude is "calculated from meteo input data". How exactly is that done? In case one had the topograph map from GDAS (I'll try to get it), could one force hysplit to use this terrain?

Henrique

barbara.stunder
Posts: 218
Joined: November 9th, 2012, 4:23 pm
Registered HYSPLIT User: Yes

Re: Ground altitude for the same point varies with start date/time

Post by barbara.stunder » September 27th, 2017, 8:05 am

The GDAS 0.5 files do not have surface height so HYSPLIT calculates it using the hydrostatic equation in the prf* subroutines. The gdas0p5 is on hybrid levels, so the subroutine is prfecm.f.

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