Radiometer intercomparison

Atmospheric boundary layer flow depends on atmospheric stability, which (in wind farms) is typically quantified with tower measurements of temperature profiles. Remote sensing of temperature profiles is possible with microwave radiometers, which will be used in the A2e WFIP2 experiment, and may be useful for improving wind energy forecasting. 

XPIA has two microwave radiometers deployed on the roof of the BAO Visitor Center; their measurements of the temperature and moisture profiles are to be compared with the 300m tower profiles as well as the profiles from the radiosonde launches. One radiometer is from NOAA, the other from CU-Boulder; both are Radiometrics MP-3000A microwave radiometers. (The CU-Boulder system is the same one as used in Friedrich et al., 2012.)

Although the two instruments should be measuring the same thing, we have discovered (thanks to some excellent quick data analysis by Laura Bianco with input from Katja Friedrich and Jim Wilczak) that there is a small offset in the ambient temperature measured between the two instruments, likely due to different surface temperature measurements. 

The radiometer data can be compared to the radiosonde profiles collected in March (based on the 15 deg radiometer scans). Especially at low temperatures (see below, left), there are deviations between the soundings and the radiometer). The mean absolute error between the radiometers and the soundings varies with height (see below, right). The larger disagreements at higher altitudes are to be expected as the sonde drifts away from the radiometer measurement volume.
 

Figure courtesy Laura Bianco

Below is the temperature comparison between the 15 degree averaged scans of the two instruments (based on data between 9 Mar and 5 Apr).

Figure courtesy Laura Bianco

Radiometrics staff have been very helpful in identifying possible sources of these differences, and additional data collection is underway to isolate the source of the deviations and identify best practices for subsequent radiometer deployments.

2015 03 18 0200Z Radiosonde Launch Report

The sky was mostly clear. The wind was very mild (less than 5 mph) at the surface. The radiosonde was launched at 02.00Z. The ascent rate was about 6.5 m/s. The boundary layer extended to around 740 mb. The atmosphere was quite stable overall. The air was near saturation at around 730 mb and 410 mb. Winds below 600 mb were mild (below 10 m/s) and the directions varied quite a bit. Strong westerlies at more than 30 kts was observed above 600 mb. The jet stream was recorded around 360 mb at 60 kts. Note that in raw data the sonde started to fall (possibly due to balloon popped) at around 175 mb before I terminated the observation. The ascent was very fast as the whole sounding only took 30 minutes. 

Written by Joseph Lee, 18 March 2015

2015 03 17 2200Z Radiosonde Launch Report

It was partly cloudy with patches of low level stratus. The wind was mild (around 5 mph) at the surface. The weather was fair in general. The radiosonde was launched at 22.00Z. The ascent rate was around 5 m/s. The boundary layer extended to around 780 mb only, then the atmosphere turned from neutral to stable. The atmosphere was quite stable overall. Winds below 600 mb were mild (from 2 to 12 m/s) and the directions varied quite a bit. Strong westerlies at more than 30 kts was observed above 600 mb. Note that in raw data the sonde started to fall (possibly due to balloon popped) at around 100 mb before I terminated the observation.  

Written by Joseph Lee, 18 March 2015

2015 03 17 1800Z Radiosonde Launch Report

Radiosonde was launched at 1836 UTC (1236 MDT local) due to visitation from middle school students from Watershed School in Boulder. Many thanks to Bill Brown of NCAR for leading the discussion and engaging with the students. In any case, the skew-T ln-p diagram is here:

As always, wind speed/wind direction vs. height also:

Remarks are as follows: Surface temperatures were warming up to the time of the launch as increase sunshine eroded low level stratus clouds. Sky was broken with stratus and having high level cirrus at time of launch. Light breezy winds at the surface. Highly variable wind speed and direction in boundary layer. Balloon ascended toward south, but turned toward north in southerly flow above the boundary layer. Daytime lapse rate and modest lapse rate above, evidence of layer ascent from earlier in day. High Relative Humidity near Boundary Layer top indicative of thin cloud intercept. (Quelet)

2015 03 17 1400Z Radiosonde Launch Report

Radiosonde was launched from the BAO visitor's center at 1400 UTC (0800 MDT local) on the dot. Conditions cold, cloudy, and windy. Here is the skew-T ln-p diagram:

In addition, of course, the wind speed/wind direction vs. height figure is also shown:

Remarks are as follows: Just past sunrise. Thick layer of altostratus clouds covering the sky. Cold temperatures at the surface. Strong winds at the surface with gusty conditions. Upslope wind from the E/SE as balloon quickly rising and moving toward the W/NW in surface layer. Strong inversion layers observed in lower troposphere. Wind direction variable in the boundary layer. Somewhat negative vertical wind shear magnitude in the boundary layer. Wind veering with height in most of lower troposphere. Well mixed and large relative humidity up to 680 hPa, probably above cloud tops. Radiosonde started descending before cutting off the data stream, so should be post processed to remove this. (Quelet)

MGAUS NCAR March 16 Radiosonde Launches

20150316 140000

Light, variable winds at the surface. Significant temperature inversion illustrates the remnants of the nighttime boundary layer. The atmosphere is fairly dry. High cirrus clouds possibly around 200mb.  Wind speed was pretty variable throughout the troposphere.

20150316 180000

Wind speeds picked up and it was a little gusty at the surface so the balloon was a bit difficult to hang on to right before launching. Still a small temperature inversion close to the surface. Temperature decreases dry adiabatically until about 650mb. Still really dry throughout the troposphere. Wind direction is variable near the surface and wind speeds pick up significantly around 500mb.

20150316 220000

Temperature decreases dry adiabatically up until about 600mb. Moisture increases slightly around 550mb, then decreases significantly. Wind speeds increase significantly around 600mb as well and become more southwesterly. Though you can’t see it on either plot, the balloon popped around 64.2mb!

20150317 020000

Was starting to get gusty right around launch time. Clouds at 550mb then quick decrease in moisture at 500mb. Strong westerly winds at and just above the boundary layer. Multiple layer of moisture throughout the troposphere.

March 15th Radiosonde Launches

An issue occurred with the 4 PM sounding. The first sonde I tried to use would not report temperature or relatively humidity measurements. After a few attempts and contacting Julie and Tim, I opened a second sonde which worked fine. The DOA sonde is labeled and resting on the front dash. Otherwise, the launches on this day went smoothly.

As can be seen from the morning 8 AM sounding, we had a strong surface inversion with cool temperatures, but the potential was already present for a warm day. Light cirrus/cirrostratus was present most of the day... It was probably around 400 mb as hinted by this sounding.

Light winds northerly winds throughout most of the boundary layer, a condition which would persist throughout the day.

This was the little balloon that could! It reached about 91 mb, which I believe is the highest so far for XPIA. An interesting double-tropopause feature appears evident. Further down, the warm day proceeds with a very dry boundary layer. There was a high amount of interference above 400 mb, which led to frequent signal interruption.

I'm not sure why the software cut this plot off so low. I wasn't able to get the rest of the sounding on the plot, but I may have missed something. Again, lower-level winds are weak. We do see more wind direction variation though.

This sonde was difficult to launch, as the near surface winds were very turbulent. As can be seen, the boundary layer is high, hot, and dry.

Weak winds continue, as does the wind shift to more southerly directions.

The final sounding demonstrates the reestablishment of the nocturnal boundary layer (thank goodness, it was too hot for March!) The entire profile has dried out compared to earlier conditions. Residual boundary layers are very apparent aloft in the temperature profile.

An interesting pattern exists here where weaker winds have a stronger westerly component. Otherwise, low-level winds continue to be weak overall.

Besides the unseasonable temperatures, no significant weather occurred on this day.

MGAUS NCAR Radiosonde launch 20150315 020000

Surface winds picked up a bit for the 8pm launch (westerly). Temperature again follows the dry adiabat until about 600mb.  Small temperature inversion around 600mb. Dry layer still holding between 600mb to about 450mb. 

Edit: U. of Wyoming sounding for 00Z shows a similar dry layer in Denver. 

Courtesy of: http://weather.uwyo.edu/

MGAUS NCAR Radiosonde launch 20150314 220000

Note: The balloon with which the first attempted launch was made was not inflated enough (16 cu ft) and did not pick the radiosonde up off the ground. As a result, the radiosonde was dragged on the ground a foot or so and had to be launched with a second balloon (20 cu ft, ~4m/s ascent rate). Hence the later launch time (22:17 UTC).

Light variable winds at the surface. Temperature follows the dry adiabat until about 550mb.  The temperature continued to decrease with height. Fairly large dry layer between 600mb up until about 400mb. Humidity then increased significantly, indicating a layer of moisture (perhaps ice clouds). 

2015 03 14 1800Z Radiosonde Launch Report

Radiosonde was launched from the BAO visitor's center at 1800 UTC (1200 MDT local) on the dot. Conditions were warm and very dry. Here is the skew-T ln-p diagram:

Also, the wind speed and wind direction vs. height figure:

Remarks are as follows:  Perfectly clear skies. Midday local. Warm at surface. Breezy to gusty surface winds. Southerly winds at surface as evidenced by initial balloon ascent. Very dry conditions throughout boundary layer. Highly variable wind speed and direction throughout boundary layer. Balloon rising fast compared to boundary layer goals due to new helium. Will decrease volume of balloon on subsequent launches.

2015 03 14 1400Z Radiosonde Launch Report

The radiosonde was launched at exactly 1400 UTC (0800 MDT local) and should serve as a good profile for LiDAR top of the hour comparisions. The skew-T log-p diagram is here:

In addition, the wind speed and wind direction vs. height figure is also shown:

Remarks are as follows: Perfectly clear skies. Several minutes after sunrise. Cool temperatures observed at the surface. Very light to calm surface winds. Faster balloon ascent rate than previous launches due to new tank of helium. Balloon went straight upward upon release. Shallow stable boundary layer inversion or so observed with boundary layer transition zone, and residual stable layer before the main tropospheric lapse rate. Wind speed light not changing substantially in the lower troposphere. Wind direction highly variable in the lower troposphere. Moisture significantly lower above 750 hPa as small storm system from previous day has moved away. Lower levels remain more moist. NNE upper level winds.

March 13th radiosonde launches

March 13th 8PM radiosonde launch

An inverted-V sounding demonstrates the dry air in the lower levels. The weak southeasterly winds at the surface did not cause any problems with the balloon and tower. The winds in general were weak at the low levels. As expected,  the nighttime inversion has started to develop in the boundary layer. The height of the boundary layer extended to approximately 610mb. 

March 13^th 4PM radiosonde launch

 

The most notable feature is the extremely dry layer around 500mb. Again, winds were light and northerly at the surface with a shift to northeasterly and then to west south westerly through the column. Clouds are more sparse and higher in altitude than at noon.

March 13th 12PM radiosonde launch

Downslope winds from the morning helped dry out the mid-levels which caused the stratus layer to dissipate. With fewer clouds, solar radiation eroded the earlier inversion. The boundary layer extended up to 750mb due to ample heating. The winds up to 350mb were northwesterly with a shift to southwesterly/westerly above this layer. Some convective clouds started to form (see image below). 

 View looking southeast from the BAO visitors center at noon.

March 13th 8AM radiosonde launch 

The day started out cool with a layer of stratus clouds. A shallow inversion was still visible near the surface. The air column was above 50% relative humidity up to 300mb, with a saturated layer between 700mb-610mb, which dried out by the noon sounding. Winds at the surface were light and westerly. Just above the surface, winds quickly changed to a more northerly direction and then again to a westerly direction.