SGP/EBBR/E7 - Windspeed threshhold too high

The wind speed sensor developed worn bearings and therefore too high a starting 
threshhold.

The data user should compare the EBBR wind speed with the SMOS wind speed to detect 
periods when the EBBR wind speed threshhold caused poor data quality.

• scalar wind speed(wind_s)
• vector wind speed(res_ws)

• vector wind speed(res_ws)
• scalar wind speed(wind_s)

• scalar wind speed(wind_s)

SGP/EBBR/E8 - Failed Temp/RH sensor

The right Temperature-Humidity sensor failed. The measured temperature gradients were 
incorrect and thus the sensible and latent heat fluxes were incorrect for this extended 
period.

The sensor was replaced March 6.

• top vapor pressure(vp_top)
• ratio of sensible/latent heat fluxes (Bowen ratio)(bowen)
• latent heat flux(e)
• Temperature of the top humidity chamber(thum_top)
• h(h)
• bottom vapor pressure(vp_bot)
• Temperature of bottom humidity sensor chamber(thum_bot)

• Temperature of the top humidity chamber(thum_top)
• Temperature of bottom humidity sensor chamber(thum_bot)
• bottom vapor pressure(vp_bot)
• top vapor pressure(vp_top)

• Temperature of right humidity sensor chamber(rr_thum_r)

SGP/ECOR/E5 - Reprocess: Time shifted -7 hours

An inadvertant power outage caused the ECOR program to shut down abnormally.  When power 
was restored, the timestamps on the ECOR files were 7 hours behind the correct time and 
the site ID was not accessed from the ECOR configuration file resulting in site ID (05) 
being replaced with "AN".

These conditions caused the ECOR files to be unrecognizable and therefore are presently 
missing in the Archive.

Correction of the timestamp and ID in the files should allow them to be processed and 
added to the Archive.

• Raw data stream - documentation not supported(raw)

• mixing ratio(mr)
• 0=real or 1=dummy value of mr(real_mr)
• covariance ut(cvar_ut)
• variance of q(var_q)
• number of valid u samples(n_good_u)
• 0=real or 1=dummy value of rho(real_rho)
• covariance of tq(cvar_tq)
• Time offset of tweaks from base_time(time_offset)
• vw covariance(cvar_vw)
• covariance uv(cvar_uv)
• skewness of variable q(skew_q)
• 0=real or 1=dummy value of lv(real_lv)
• vector averaged wind direction(wind_dir)
• mean value of out of range values and spikes of c -9999 if no spikes(mean_spk_c)
• number of valid q samples(n_good_q)
• mean value of \spike\ u samples(mean_spk_u)
• covariance of qc(cvar_qc)
• number of t samples removed due to spikes(n_spk_t)
• skewness of variable c(skew_c)
• mean value of \spike\ v samples(mean_spk_v)
• rotated mean v(mean_rot_v)
• condensation pressure(cp)
• rotated covariance vq(cvar_rot_vq)
• rotated covariance ut(cvar_rot_ut)
• rotated covariance uw(cvar_rot_uw)
• skewness of variable u(skew_u)
• rotated covariance vw(cvar_rot_vw)
• rotated covariance uv(cvar_rot_uv)
• kurtosis of variable q(kurt_q)
• number of valid v samples(n_good_v)
• skewness of variable t(skew_t)
• variance of c(var_c)
• vector averaged wind speed(wind_spd)
• number of bad or out of range t samples(n_bad_t)
• lat(lat)
• number of v samples removed due to spikes(n_spk_v)
• latent heat flux(lv_e)
• Water vapor density (q)(mean_q)
• number of u samples removed due to spikes(n_spk_u)
• number of samples with \IRGA hardware problem\ flag(n_bad_irga)
• variance of w(var_rot_w)
• number of bad or out of range w samples(n_bad_w)
• number of samples with bad sonic status flag(n_bad_son_ic)
• Dummy altitude for Zeb(alt)
• uw covariance(cvar_uw)
• rotated covariance vt(cvar_rot_vt)
• number of w samples removed due to spikes(n_spk_w)
• mean horizontal wind speed(mean_rot_u)
• covariance uq(cvar_uq)
• Retrieved water vapor density profile(rho)
• number of c samples removed due to spikes(n_spk_c)
• number of q samples removed due to spikes(n_spk_q)
• number of valid c samples(n_good_c)
• rotated covariance wc(cvar_rot_wc)
• standard deviation of wind elevation angle(std_elev)
• variance of variable v(var_v)
• covariance wc(cvar_wc)
• time(time)
• average atmospheric pressure (IGRA internal sensor)(atm_pres)
• rotated covariance vc(cvar_rot_vc)
• latent heat of vaporization(lv)
• Virtual temperature (T)(mean_t)
• kurtosis of variable c(kurt_c)
• number of bad or out of range u samples(n_bad_u)
• covariance vt(cvar_vt)
• rotated covariance wq(cvar_rot_wq)
• vertical (elevation) wind angle(elev)
• kurtosis of variable t(kurt_t)
• number of valid t samples(n_good_t)
• number of samples with IRGA optical path blocked flag(n_bad_irga_light)
• covariance uc(cvar_uc)
• number of bad or out of range v samples(n_bad_v)
• kurtosis of variable u(kurt_u)
• Friction velocity(ustar)
• momentum flux (dynamic)(k)
• 0=real or 1=dummy value of cp(real_cp)
• variance of variable w(var_w)
• number of bad or out of range q samples(n_bad_q)
• skewness of variable v(skew_v)
• skewness of variable w(skew_w)
• variance of variable u(var_u)
• average voltage of IRGA cooler(mean_cooler)
• rotated covariance uq(cvar_rot_uq)
• Down-boom wind velocity (u)(mean_u)
• kurtosis of variable v(kurt_v)
• variance of t(var_t)
• variance of u(var_rot_u)
• variance of v(var_rot_v)
• kurtosis of variable w(kurt_w)
• covariance vc(cvar_vc)
• lon(lon)
• covariance of tc(cvar_tc)
• base time(base_time)
• number of bad or out of range c samples(n_bad_c)
• wT covariance(cvar_wt)
• h(h)
• number of valid w samples(n_good_w)
• rotated covariance uc(cvar_rot_uc)
• CO2 flux(fc)
• mean co2 concentration (c)(mean_c)
• rotated covariance wt(cvar_rot_wt)
• Vertical angle of wind(phi)
• average temperature (IGRA internal sensor)(temp_irga)
• mean value of out of range values and spikes of q -9999 if no spikes(mean_spk_q)
• covariance wq(cvar_wq)
• Vertical wind velocity (w)(mean_w)
• mean value of \spike\ w samples(mean_spk_w)
• standard deviation of wind direction(std_wind_dir)
• Cross-boom wind velocity (v)(mean_v)
• rotated mean w(mean_rot_w)
• mean value of out of range values and spikes of t -9999 if no spikes(mean_spk_t)
• covariance vq(cvar_vq)

SGP/EBBR/E4 - Wind Direction Stuck at Zero

The wind direction sensor was stuck at zero.

• wind direction (relative to true north)(wind_d)
• standard deviation of wind direction (sigma theta)(sigma_wd)
• vector wind speed(res_ws)

• wind direction (relative to true north)(wind_d)
• vector wind speed(res_ws)
• standard deviation of wind direction (sigma theta)(sigma_wd)

• Wind direction (relative to true north)(mv_wind_d)

SGP/ECOR/E21 - Intermittent incorrect flux measurements

At various times during the period, the LI-7500 CO2/H2O serial and analog signals from the 
LI-7500 were missing, but usually not at the same time.

When the CO2/H2O serial datastream was missing, the Pressure and Temperature were missing; 
this did not, in itself, result in incorrect fluxes, as default values for pressure and 
temperature are automatically used.

Fluxes were incorrect when the CO2/H2O analog datastream was missing; these
times are identified by the qc checks.

• latent heat flux(lv_e)
• covariance wc(cvar_wc)
• average atmospheric pressure (IGRA internal sensor)(atm_pres)
• covariance wq(cvar_wq)
• CO2 flux(fc)
• average temperature (IGRA internal sensor)(temp_irga)

SGP/EBBR/E4 - Instrument problem

Wind direction was flat lining near zero and incorrect.

• wind direction (relative to true north)(wind_d)
• standard deviation of wind direction (sigma theta)(sigma_wd)

• wind direction (relative to true north)(wind_d)
• standard deviation of wind direction (sigma theta)(sigma_wd)

• Wind direction (relative to true north)(mv_wind_d)

SGP/ECOR/E5 - Flux Measurements Incorrect

The ECOR datastream was corrupted; this happens when the ECOR program produces a 
datastream of the wrong length (i.e., leaves one or more measurements out).

Fluxes and some other measurements are incorrect.

Note: Mentor reports reprocessing will not correct this problem.

• latent heat flux(lv_e)
• CO2 flux(fc)
• h(h)

SGP/ECOR/E5 - Flux Data Incorrect

CO2 flux (lv_e) and latent heat flux (fc) were incorrect because the sonic anemometer was 
not working.

• latent heat flux(lv_e)
• CO2 flux(fc)
• Water vapor density (q)(mean_q)
• variance of q(var_q)
• mean co2 concentration (c)(mean_c)
• covariance wc(cvar_wc)
• covariance wq(cvar_wq)
• variance of c(var_c)

SGP/EBBR/E20 - Reprocess: Wind Direction 20 Degrees Low

The EBBR wind direction was found to be misaligned 20 degrees low. 

This bias should have had no effect on the res_ws or sigma_wd measurements.

• wind direction (relative to true north)(wind_d)

• Wind direction (relative to true north)(mv_wind_d)

• wind direction (relative to true north)(wind_d)

SGP/EBBR/E27 - Multiplexer #2 failure

A problem with the #2 Multiplexer caused a large number of measurements to be incorrect.  
Sensible and latent heat fluxes were often affected.

• Exchange mechanism position indicator (0 to 15 min)(home_15)
• net radiation(q)
• ratio of sensible/latent heat fluxes (Bowen ratio)(bowen)
• 5 cm soil heat flow corrected for soil moisture content, site 2(c_shf2)
• latent heat flux(e)
• 5 cm soil heat flow, site 5(shf5)
• soil heat flow, site 5(g5)
• soil heat flow, site 3(g3)
• bottom vapor pressure(vp_bot)
• 5 cm soil heat flow corrected for soil moisture content, site 5(c_shf5)
• Top humidity(hum_top)
• 5 cm soil heat flow corrected for soil moisture content, site 3(c_shf3)
• soil heat flow, site 2(g2)
• top air temperature(tair_top)
• soil heat flow, site 1(g1)
• 5 cm soil heat flow, site 2(shf2)
• top vapor pressure(vp_top)
• Exchange mechanism position indicator (15 to 30 min)(home_30)
• 5 cm soil heat flow corrected for soil moisture content, site 4(c_shf4)
• 5 cm soil heat flow, site 3(shf3)
• 5 cm soil heat flow corrected for soil moisture content, site 1(c_shf1)
• 5 cm soil heat flow, site 4(shf4)
• Bottom humidity(hum_bot)
• 5 cm soil heat flow, site 1(shf1)
• bottom air temperature(tair_bot)
• average surface soil heat flow(ave_shf)
• h(h)
• soil heat flow, site 4(g4)

• net radiation(q)
• Bottom humidity(hum_bot)
• Home signal(home)
• top vapor pressure(vp_top)
• bottom air temperature(tair_bot)
• top air temperature(tair_top)
• Retrieved pressure profile(pres)
• Top humidity(hum_top)
• bottom vapor pressure(vp_bot)

• Soil heat flow 1(mv_hft1)
• Net radiation(mv_q)
• Left air temperature(tair_l)
• Soil heat flow 3(mv_hft3)
• Soil heat flow 4(mv_hft4)
• Soil heat flow 5(mv_hft5)
• Right relative humidity(mv_hum_r)
• Atmospheric pressure(mv_pres)
• Right air temperature(tair_r)
• Left relative humidity(mv_hum_l)
• Soil heat flow 2(mv_hft2)
• Home signal(mv_home)

SGP/EBBR/E4 - Wind Direction Incorrect

The EBBR wind direction sat at about 60 degrees from 08/09 0230 GMT through 08/24 1930 GMT 
and was incorrect.

• wind direction (relative to true north)(wind_d)
• standard deviation of wind direction (sigma theta)(sigma_wd)
• vector wind speed(res_ws)

• wind direction (relative to true north)(wind_d)
• vector wind speed(res_ws)
• standard deviation of wind direction (sigma theta)(sigma_wd)

• Wind direction (relative to true north)(mv_wind_d)

SGP/EBBR/E20 - Reprocess: Wind Direction 65 Degrees Low

The wind direction sensor reported wind directions that were 65 degrees too low because of 
a mis-alignment.

This bias should have no effect on the res_ws or sigma_wd measurements.

The wind direction data could be re-processed by adding 65 degrees.

• wind direction (relative to true north)(wind_d)

• Wind direction (relative to true north)(mv_wind_d)

• wind direction (relative to true north)(wind_d)

SGP/EBBR/E9 - Net Radiation Incorrect

There was water in the net radiometer.  

The net radiation data was incorrect.

• Net radiation(mv_q)

• net radiation(q)

• latent heat flux(e)
• h(h)
• net radiation(q)

SGP/EBBR/E27 - Measurements offscale

All J-panel 4 measurements (soil heat flows, net radiation, air temperatures, home 
signals, pressure, vapor pressure) were sometimes offscale or otherwise incorrect.  J-Panel was 
replaced 20080326 correcting the problem.

• net radiation(q)
• top air temperature(tair_top)
• Retrieved pressure profile(pres)
• Home signal(home)
• bottom vapor pressure(vp_bot)
• top vapor pressure(vp_top)
• bottom air temperature(tair_bot)

• 5 cm soil heat flow corrected for soil moisture content, site 3(c_shf3)
• Exchange mechanism position indicator (0 to 15 min)(home_15)
• soil heat flow, site 2(g2)
• net radiation(q)
• top air temperature(tair_top)
• 5 cm soil heat flow corrected for soil moisture content, site 2(c_shf2)
• soil heat flow, site 1(g1)
• latent heat flux(e)
• Retrieved pressure profile(pres)
• 5 cm soil heat flow, site 5(shf5)
• top vapor pressure(vp_top)
• 5 cm soil heat flow, site 2(shf2)
• Exchange mechanism position indicator (15 to 30 min)(home_30)
• 5 cm soil heat flow corrected for soil moisture content, site 4(c_shf4)
• 5 cm soil heat flow, site 3(shf3)
• soil heat flow, site 5(g5)
• 5 cm soil heat flow, site 4(shf4)
• 5 cm soil heat flow corrected for soil moisture content, site 1(c_shf1)
• soil heat flow, site 3(g3)
• bottom air temperature(tair_bot)
• bottom vapor pressure(vp_bot)
• 5 cm soil heat flow, site 1(shf1)
• 5 cm soil heat flow corrected for soil moisture content, site 5(c_shf5)
• h(h)
• soil heat flow, site 4(g4)

• Right air temperature(tair_r)
• Soil heat flow 1(mv_hft1)
• Net radiation(mv_q)
• Left air temperature(tair_l)
• Soil heat flow 3(mv_hft3)
• Soil heat flow 4(mv_hft4)
• Soil heat flow 5(mv_hft5)
• Soil heat flow 2(mv_hft2)
• Atmospheric pressure(mv_pres)
• Home signal(mv_home)

SGP/EBBR/E7  - Wind Speed Frozen Stopped

Freezing rain stopped wind speed sensor.

• scalar wind speed(wind_s)
• vector wind speed(res_ws)

• vector wind speed(res_ws)
• scalar wind speed(wind_s)

• scalar wind speed(wind_s)

SGP/ECOR/E24 - Water Vapor Density Incorrect

Mean Water Vapor Density (mean_q) often did not trend well with the co-located SMOS and 
sometimes jumped downwards approximately 200 to 300 mmol/m^3.  Some of the instances were 
clearly a result of contamination by precipitation, but others were not; the latent heat 
flux was sometimes affected.

It was determined that all instances of this behavior from the beginning of 2008 through 
the beginning date of this DQR were caused by precipitation/dew/frost.

• Water vapor density (q)(mean_q)
• latent heat flux(lv_e)

SGP/EBBR/E13 - Wind direction failure

The EBBR wind direction was stuck at 135 degrees; this reading indicates a failure of the 
sensor electronics.

• Wind direction (relative to true north)(mv_wind_d)

• vector wind speed(res_ws)
• wind direction (relative to true north)(wind_d)
• standard deviation of wind direction (sigma theta)(sigma_wd)

• standard deviation of wind direction (sigma theta)(sigma_wd)
• wind direction (relative to true north)(wind_d)
• vector wind speed(res_ws)

SGP/EBBR/E20 - Wind Direction 50 Degrees High

The wind direction was offset high about 50 degrees.

• wind direction (relative to true north)(wind_d)

• Wind direction (relative to true north)(mv_wind_d)

• wind direction (relative to true north)(wind_d)

SGP/EBBR/E4 - AEM Blown Fuse, Sensible and Latent Heat Fluxes Incorrect

The AEM Fuse was blown, the AEM was not switching, and thus sensible and latent heat flux 
measurements were incorrect.

• h(h)
• ratio of sensible/latent heat fluxes (Bowen ratio)(bowen)
• latent heat flux(e)

SGP/ECOR/E24 - Half Hours of Data Missing

Individual half hours of data were missing infrequently because of a UPS
problem.  The extent of missing data is minimal, with only a few to several half hours 
missing most months.

Data quality of the surrounding data times was not affected.

• covariance uq(cvar_uq)
• covariance of qc(cvar_qc)
• variance of v(var_rot_v)
• covariance wc(cvar_wc)
• 0=real or 1=dummy value of mr(real_mr)
• 0=real or 1=dummy value of rho(real_rho)
• Vertical angle of wind(phi)
• number of t samples removed due to spikes(n_spk_t)
• covariance uc(cvar_uc)
• number of u samples removed due to spikes(n_spk_u)
• Virtual temperature (T)(mean_t)
• variance of variable v(var_v)
• variance of u(var_rot_u)
• rotated covariance wt(cvar_rot_wt)
• skewness of variable u(skew_u)
• latent heat of vaporization(lv)
• variance of w(var_rot_w)
• rotated covariance uc(cvar_rot_uc)
• 0=real or 1=dummy value of cp(real_cp)
• covariance of tq(cvar_tq)
• mean value of \spike\ w samples(mean_spk_w)
• skewness of variable t(skew_t)
• skewness of variable c(skew_c)
• Friction velocity(ustar)
• CO2 flux(fc)
• covariance wq(cvar_wq)
• latent heat flux(lv_e)
• number of valid v samples(n_good_v)
• mean value of out of range values and spikes of c -9999 if no spikes(mean_spk_c)
• covariance of tc(cvar_tc)
• kurtosis of variable v(kurt_v)
• mean value of \spike\ v samples(mean_spk_v)
• condensation pressure(cp)
• number of valid w samples(n_good_w)
• rotated covariance wc(cvar_rot_wc)
• skewness of variable q(skew_q)
• Time offset of tweaks from base_time(time_offset)
• skewness of variable w(skew_w)
• kurtosis of variable w(kurt_w)
• number of bad or out of range c samples(n_bad_c)
• rotated mean w(mean_rot_w)
• kurtosis of variable t(kurt_t)
• number of valid t samples(n_good_t)
• number of bad or out of range v samples(n_bad_v)
• Vertical wind velocity (w)(mean_w)
• mixing ratio(mr)
• number of samples with IRGA optical path blocked flag(n_bad_irga_light)
• Retrieved water vapor density profile(rho)
• number of q samples removed due to spikes(n_spk_q)
• mean value of out of range values and spikes of t -9999 if no spikes(mean_spk_t)
• number of bad or out of range w samples(n_bad_w)
• 0=real or 1=dummy value of lv(real_lv)
• Dummy altitude for Zeb(alt)
• h(h)
• covariance vc(cvar_vc)
• rotated covariance wq(cvar_rot_wq)
• kurtosis of variable u(kurt_u)
• skewness of variable v(skew_v)
• kurtosis of variable c(kurt_c)
• rotated covariance vc(cvar_rot_vc)
• covariance uv(cvar_uv)
• number of bad or out of range u samples(n_bad_u)
• number of w samples removed due to spikes(n_spk_w)
• number of valid c samples(n_good_c)
• mean co2 concentration (c)(mean_c)
• variance of t(var_t)
• Water vapor density (q)(mean_q)
• number of bad or out of range t samples(n_bad_t)
• number of valid u samples(n_good_u)
• rotated mean v(mean_rot_v)
• uw covariance(cvar_uw)
• number of c samples removed due to spikes(n_spk_c)
• Cross-boom wind velocity (v)(mean_v)
• covariance ut(cvar_ut)
• mean horizontal wind speed(mean_rot_u)
• covariance vq(cvar_vq)
• rotated covariance vt(cvar_rot_vt)
• covariance vt(cvar_vt)
• mean value of \spike\ u samples(mean_spk_u)
• vector averaged wind direction(wind_dir)
• rotated covariance ut(cvar_rot_ut)
• standard deviation of wind elevation angle(std_elev)
• average voltage of IRGA cooler(mean_cooler)
• wT covariance(cvar_wt)
• momentum flux (dynamic)(k)
• average atmospheric pressure (IGRA internal sensor)(atm_pres)
• mean value of out of range values and spikes of q -9999 if no spikes(mean_spk_q)
• standard deviation of wind direction(std_wind_dir)
• vertical (elevation) wind angle(elev)
• variance of variable w(var_w)
• variance of c(var_c)
• rotated covariance uw(cvar_rot_uw)
• base time(base_time)
• variance of q(var_q)
• number of samples with bad sonic status flag(n_bad_son_ic)
• rotated covariance uq(cvar_rot_uq)
• vw covariance(cvar_vw)
• lat(lat)
• rotated covariance vw(cvar_rot_vw)
• number of v samples removed due to spikes(n_spk_v)
• rotated covariance uv(cvar_rot_uv)
• rotated covariance vq(cvar_rot_vq)
• number of bad or out of range q samples(n_bad_q)
• time(time)
• variance of variable u(var_u)
• vector averaged wind speed(wind_spd)
• lon(lon)
• kurtosis of variable q(kurt_q)
• number of valid q samples(n_good_q)
• average temperature (IGRA internal sensor)(temp_irga)
• Down-boom wind velocity (u)(mean_u)
• number of samples with \IRGA hardware problem\ flag(n_bad_irga)

SGP/EBBR/E4 - Reprocess: Wind Direction Incorrect

The wind direction was misaligned by 180 degrees. If the wind direction was 180 degrees or 
less, add 180 degrees to give the correct direction.  If the wind direction was greater 
than 180 degrees, subtract 180 degrees to give the correct direction.

• wind direction (relative to true north)(wind_d)

• wind direction (relative to true north)(wind_d)

• Wind direction (relative to true north)(mv_wind_d)

SGP/EBBR/E8 - Wind Direction Incorrect

The wind direction flatlined at times at 135 degrees (an indication of failed electronics) 
and at other times trended correctly with the co-located SMOS but differed from it by 15 
to 100 degrees.

• standard deviation of wind direction (sigma theta)(sigma_wd)
• wind direction (relative to true north)(wind_d)

• wind direction (relative to true north)(wind_d)
• standard deviation of wind direction (sigma theta)(sigma_wd)

• Wind direction (relative to true north)(mv_wind_d)

SGP/EBBR/E15 - Water in dome

There was water in the bottom dome of the net radiometer.

Net radiation, and sensible and latent heat fluxes were 
incorrect during the period.

• Net radiation(mv_q)

• net radiation(q)
• latent heat flux(e)
• h(h)

• net radiation(q)

SGP/EBBR/E15 - Soil Heat Flow #4 Incorrect

Soil heat flux #4 produced too large a soil heat flow at times, resulting in it exceeding 
the qc check limit and causing sensible and latent heat fluxes to be incorrect.

• Soil heat flow 4(mv_hft4)

• latent heat flux(e)
• 5 cm soil heat flow, site 4(shf4)
• 5 cm soil heat flow corrected for soil moisture content, site 4(c_shf4)
• average surface soil heat flow(ave_shf)
• soil heat flow, site 4(g4)
• h(h)

SGP/EBBR/E20 - Wind Direction Incorrect

The wind direction differed from the co-located SMOS by 50 deg during part of the stated 
period and the electronics had failed completely resulting in a constant 135 degrees for 
the following dates and times:
08/15 0230-0430, 0830-1530 and 09/03 0200-0300, 0500 - 09/10 2230.

Sensible and latent heat fluxes were not affected by this problem.

• standard deviation of wind direction (sigma theta)(sigma_wd)
• wind direction (relative to true north)(wind_d)
• vector wind speed(res_ws)

• Wind direction (relative to true north)(mv_wind_d)

• wind direction (relative to true north)(wind_d)
• vector wind speed(res_ws)
• standard deviation of wind direction (sigma theta)(sigma_wd)