SkewT 0.1.2

Plots and analyses atmospheric profile data

SkewT provides a few useful tools to help with the plotting and analysis of upper atmosphere data. In particular it provides some useful classes to handle the awkward skew-x projection (provided by Ryan May, see notes in source code and LICENSE.txt).

It’s most basic implementation is to read a text file of the format provided by the University of Wyoming’s website:

http://weather.uwyo.edu/upperair/sounding.html

Typical usage often looks like this:

#!/usr/bin/env python

from skewt import SkewT
sounding = SkewT.Sounding(filename="soundingdata.txt")
sounding.plot_skewt()

Alternatively you may input the required data fields in a dictionary. The dictionary must have as a minimum the fields PRES and TEMP corresponding to pressure (hPa) and temperature (deg C). Soundings will typically have a dew point temperature trace and wind barbs as well, so it’s best to include the dewpoint temp DWPT (deg C), wind speed SKNT (knots) and wind direction in degrees WDIR. Other fields may be included as per the docstring:

#!/usr/bin/env python

from skewt import SkewT
sounding = SkewT.Sounding(data=data_dict)
sounding.plot_skewt

News

I was so thrilled to see that there were something like 80 downloads in the first week that I dropped everything else and pushed through some changes I had been meaning to make. Thanks for your interest in this package and I’d love to hear your feedback: thomas.chubb AT monash.edu

Here’s a summary of what’s new in this release:

• Added a parcel ascent routine based on provided pressure, dewpoint and temperature. This routine adds some characteristics to the plot in the upper LHS. TODO: initialise parcels automatically, calculate CAPE and CIN and Precipitable water…

• Removed reliance on rcParams to make the figure look pretty. Did this because I got annoyed (and I’m sure that others will too) at what happens to graphs plotted subsequently… they end up with yellow axes etc.

• Improved some of the aesthetics of the plot… moved standard atmosphere height axis to right hand side.

Sounding Files

The format for the sounding files is very specific (sorry). You are best off using the example in “examples” as a template. Here’s a sample of the first few lines:

94975 YMHB Hobart Airport Observations at 00Z 02 Jul 2013

-----------------------------------------------------------------------------
   PRES   HGHT   TEMP   DWPT   RELH   MIXR   DRCT   SKNT   THTA   THTE   THTV
    hPa     m      C      C      %    g/kg    deg   knot     K      K      K
-----------------------------------------------------------------------------
 1004.0     27   12.0   10.2     89   7.84    330     14  284.8  306.7  286.2
 1000.0     56   12.4   10.3     87   7.92    325     16  285.6  307.8  286.9
  993.0    115   12.8    9.7     81   7.66    311     22  286.5  308.1  287.9

The script defines columns by character number so you really do have to get the format exactly right. One day I will get around to writing a routine to output the text files properly.

Parcel Ascent (New in version 0.1.2!)

Simple routine to calculate the characteristics of a parcel initialised with pressure, temperature and dew point temperature. You could do it like this:

from skewt import SkewT

sounding=SkewT.Sounding("examples/94975.2013070200.txt")
sounding.make_skewt_axes()
sounding.add_profile(color='r',lw=2)
sounding.lift_parcel(1004.,17.4,8.6)
draw()

The parcel properties are manually input at this point. For the example above (BOM), I believe that the temperature was the forecast maximum for the day and the dewpoint temp was derived by taking the average mixing ratio from the lowest 50 (100??) mb and calculating the corresponding dew point temperature for the surface pressure at the sounding time.

To-Do List

• I want to do some basic diagnostics given the lifted parcel. This shouldn’t be hard it’s just that I have more pressing things to do. If anybody out there wants to adapt/contribute routines that they have I’d be most grateful. Send your fan/hate mail to thomas.chubb AT monash.edu

• Hodographs?

Contributors

The initial SkewX classes were provided by a fellow called Ryan May who was a student at OU. I have not made contact with Ryan other than to download his scripts and modify them for my own purposes.

Hamish Ramsay has promised to at least think about adding some extra diagnostics.