Friday June 18, 2021 - Brief Low Visibility
(Morning Haze Layer)
Observation from instruments on the MetTrailer indicated a
brief, low visibility event on the morning of June 18, 2021. Between
11:00 and 11:10 UTC (6:00 - 6:10 CST), the visibility is reduced to
between 1-2 km (Figure 1).
Five minutes before the low visibility event, the temperature fell
from approximately 13.5 ℃ to 12.0 ℃ before returning to above 13.0 ℃
(Figure 2). The temperature
change had a corresponding change in relative humidity to 66 %
(Figure 3). The Deeplens camera
obtained an image at 10:59 UTC (5:59 CST) showing a haze layer above
the field (Figure 4). This haze layer is what the CS125 Present Weather
and Visibility Sensor detected with the low
visibility of 1-2 km. The CS125 is mounted on the MetTrailer roof,
which is in an field approximately 30 m behind the Deeplens field
observational camera. A second DeepLens camera shows a view from the
MetTrailer towards the field (Figure 5).
The change in relative humidity resulted in the aerosols taking up
water that changed size sufficiently resulting in the haze layer.
The aerosols under went deliquescence;
whereby, their strong affinity of the aerosols for water resulted in
the aerosols absorbing moisture from the atmosphere and forming an
aqueous solution aerosol. The aqueous solution aerosol can have a
diameter 3-4 times larger than their dry (non deliquecence state)
aerosols.
Figure 1: Image showing one minute measurements of visibility from
the CS125
Present Weather and Visibility Sensor on the MetTrailer
located at the Delene's residents. The CS125 is mounted
on the
MetTrailer roof at a height of 4 m AGL. The MetTrailer
is in an field approximately 30 m behind the Deeplens field
observational camera. Measurements are over an one
hour period (10:30-11:30 UTC, 5:30 - 6:30 CST) on 18 June 2021.
Figure 2: Image showing one minute measurements of temperature
from the CS125
Present Weather and Visibility Sensor on the MetTrailer
located at the Delene's residents. The CS125
is mounted on the MetTrailer
roof at a height of 4 m AGL. The
MetTrailer is in an field
approximately 30 m behind the Deeplens field observational
camera. Measurements are
over an one hour period (10:30-11:30 UTC, 5:30 - 6:30 CST) on 18
June 2021.
Figure 3: Image showing one minute measurements of relative
humidity from the CS125 Present Weather
and Visibility Sensor on the MetTrailer
located at the Delene's residents. The
CS125 is mounted on the
MetTrailer roof at a height of 4 m AGL.
The
MetTrailer is in an field
approximately 30 m behind the Deeplens field
observational camera. Measurements
are over an one hour period (10:30-11:30 UTC, 5:30 - 6:30 CST) on
18 June 2021.
Figure 4: Set of three images ten minutes apart from the Deeplens
camera on the MetTrailer
located at the Delene's residents. Images are at 10:49, 10:59, and
11:09 UTC (5:49, 5:59, and 6:09 CST).
Figure 5: Image showing the view from the MetTrailer with a
second Deeplens camera at 11:00 UTC (6:00 CST). The
images in Figure 4 are from Deeplens camera directly behind the
further yellow and back sign.
David Delene's Blog
Page
David Delene's Home Page