Pressure levels for heights AGL between 100 and 250 m in HRRR

[rthedin]

Working my way through PR #16, I noticed some problems on the HRRR interface.

When getting data from HRRR using wind_velocity_direction_at_altitude, at any height AGL height_above_ground above 100 m, we fall into the following else to get the appropriate pressure level:

SSRS/ssrs/hrrr/hrrr.py

Lines 350 to 363 in a9114c7

	if height_above_ground_m > 0.0 and height_above_ground_m < 45.0:
	grib_field = f'{varname}:10 m above ground:anl'
	u_data_var = 'u10'
	v_data_var = 'v10'
	elif height_above_ground_m >= 45.0 and height_above_ground_m < 100.0:
	grib_field = f'{varname}:80 m above ground:anl'
	u_data_var = 'u'
	v_data_var = 'v'
	else:
	nearest_pressures = self.nearest_pressures(ground_level_m)
	closest_pressure_above = nearest_pressures['closest_pressure_above']
	grib_field = f'{varname}:{closest_pressure_above} mb'
	u_data_var = 'u'
	v_data_var = 'v'

where ground_level_m is used as an argument to nearest_pressures. However, oftentimes the call to wind_velocity_direction_at_altitude does not include ground_level_m, but rather height_above_ground_m. The ground_level_m is zero by default:

SSRS/ssrs/hrrr/hrrr.py

Line 260 in a9114c7

ground_level_m=0.0,

According to the nearest_pressures function's docstring, h is the height above sea level:

SSRS/ssrs/hrrr/hrrr.py

Lines 92 to 93 in a9114c7

	h: float
	Height above sea level in meters

so I'm not sure if it is appropriate to use height_above_ground_m

What should we use here? Not specifying ground_level_m does not work because of the default 0 (and would not even be appropriate). Should we first get the ground level and then combine it with the height AGL?

Right now, in the latest commit from PR #16, I replaced line 359 above with

SSRS/ssrs/hrrr/hrrr.py

Line 376 in 43a728f

nearest_pressures = self.nearest_pressures(height_above_ground_m)

However, I do understand that this is not really appropriate.

What would be appropriate path forward here?

[rthedin]

@ewquon @rimplesandhu

[ewquon]

Hi @rthedin, good catch. I think it should be ground_level_m + height_above_ground_m to give the altitude above sea level. However, I don't think we need to be too concerned about this because we need to rework nearest_pressures() anyway and--correct me if I'm wrong @rimplesandhu--I don't think this is currently used. I think we can use the hypsometric equation instead of a hard-coded lookup table.

[rimplesandhu]

No, I have only focused on 10 and 80 m for annotating telemetry data