Soundings

What is a Sounding?

Used to plot the vertical distribution of temperature, dew-point, and pressure obtained by a radiosonde

It creates a vertical profile of the atmosphere!

Radiosondes can obtain data up to a height of around 30 km

Image 1: Example of how atmospheric soundings are collected. Radiosondes are small electronic devices that are attached to weather balloons. As the balloon rises through the atmosphere, the device records various atmospheric variables and transmits them to a receiver on the surface.

Image 2: A person standing in a snowy environment is about to release an atmospheric sounding.

Skew-T Log-P Diagram

Skew-T = Isotherms (see image below)

Lines of equal temperature that are slanted or skewed

Log-P = Isobars (see image below)

Lines of equal pressure that are spaced logarithmically

Image 3: The temperature lines on a Skew-T diagram are evenly spaced along the horizontal axis and slanted at a 45-degree angle towards the right.

Image Description: Skew-T Log-P (Isotherms)

Pressure (mb) is recorded to the left of the graph. Temperature (C) is recorded on the bottom (x-axis) and is repeated around the right y-axis.

*Note: the lines are of constant temperature, so whether you are looking at them from the x or y axis shouldn't matter, as each line has its value repeated.

Isotherms in this image are highlighted as teal diagonal lines, crossing the isobars

Image 4: The pressure lines on a skew-T are located on the vertical axis. Pressure values decrease vertically along the axis. Lines are closer together near the bottom and gradually become more spread out as you move towards the top.

Image Description: Skew-T Log-P (Isobars)

Pressure (mb) is recorded to the left of the graph. Temperature (C) is recorded on the bottom (x-axis) and gets wrapped around the right y-axis.

Isobars in this image are highlighted as orange horizontal lines, crossing the isotherms

Example Sounding

Image 5: Skew-T Log-P Diagram. Pressure is plotted on the vertical axis, with a logarithmic scale, and the temperature is plotted skewed at a 45° angle. the green line on the left represents the Dew-Point Temperature Td ; the red line on the right represents the Temperature (T).

Each data point is plotted and then connected with a line
Reminder: Td should never be greater than T!

Important Features

Inversion: Any segment in the troposphere where temperature increases with height

Image 6: Important feature (temperature inversion). This Skew-T Log-P diagram highlights how the temperature line (on the right in red) shows a positive slope up until a certain point. This positive slope in the temperature line is what represents the inversion Positive slope: temperature is increasing with height.

Possible Cloud Layers: Any segments where the difference between the temp and dew point temperature is 5ºC or less

Image 7: Important feature (Possible Cloud Layers). This Skew-T Log-P diagram highlights how the space between the Dew-Point (left in green) and Temperature (right in red) lines can indicate cloud layers. If this space is less than 5ºC, then there is a possible cloud layer. This image shows an area of approximately 5ºC difference highlighted in blue.

Freezing level: The level at which the temperature drops below 0ºC. If the entire temperature profile is below zero, the freezing level is reported at the surface (usually 1000mb).

Image 8: Important feature (Freezing Level). This Skew-T Log-P diagram highlights how to find the freezing level. Start at the 0ºC isotherm. Follow the skewed line to where it meets the recorded red line (representing temperature). Follow the isobar (horizontal line) to the edge of the graph and record the pressure level associated with it.

Tropopause Height: Boundary between troposphere and stratosphere, where the temp increases with height. Look just below where the temp starts increasing, usually around 250mb.

Image 9: Important feature (Tropopause Height). This Skew-T Log-P diagram highlights how the temperature line (on the right in red) changes a positive slope near the top of the diagram. This positive slope will continue to the top of the diagram. At the point of this inversion is the tropopause (boundary between the troposphere and stratosphere where temperature begins to increase with height).

Wind Barbs

Winds can also be plotted on a sounding to visualize how wind is changing with height (see example sounding below)
Wind barb is the direction the wind is coming from, given in degrees

Image 10: Wind speeds on barbs are constructed using 3 different pieces. A half-line equals 5 knots, a full-line equals 10 knots, and a triangular-shaped flag equals 50 knots. These three barbs are combined to represent the wind speed to the closest 5 knots. Examples: 15 knots is one full-line and one half-line. 175 knots is three flags, two full-lines, and one half-line.

Image 11 : Wind Direction With respect to the Surface Station Model Center circle with a "+" in the center North is indicated as 0° East is indicated as 90° South is indicated as 180° West is indicated as 270°

Image 12: Atmospheric sounding example plotted on a skew-T.

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