Add downdraft CAPE calculation #823

jrleeman · 2018-04-24T14:43:23Z

Closes #728 by adding a downdraft CAPE calculation. As it stands there are still some things to discuss/clear up:

How should we let folks specify custom bounds for the integration? A custom parcel?
Need to add tests

The main difficulty currently is that this does not appear to compare well with the SPC DCAPE values. Looking at their results I'm not sure there isn't a bug on one or both ends. Take the two soundings below. To me one should have positive DCAPE, the other negative as in one the parcel path is to the left of the environmental temperature, and it is to the right in the other. Also, to get values anywhere near as large as these I have to integrate the entire lower 400 hPa, not the surface up to the minimum theta-e in the lowest 400 hPa. Any comments welcome as we need to nail this down before testing and merging.

stickler-ci · 2018-04-27T19:04:09Z

metpy/calc/thermo.py

+                                                    depth=pressure[-1] - top_pressure)
+
+
+    # Calculate the difference in profile and environmental temperature to integrate


E303 too many blank lines (2)

jrleeman · 2018-05-01T22:43:33Z

Ok working on this some more there are some implementation details to think about. The kwargs bottom and top make sense when using the default parcel. But when using a parcel kwarg that is currently a tuple of pressure and temperature at which we want to start a parcel. It would then go down the moist adiabat to the surface. Then the bottom and top_pressure arguments are ambiguous as to their utilization. Maybe we only take the profile as a complete profile that the user wants? Thoughts @dopplershift?

dopplershift

It looks liketop_pressure and bottom are actually used when parcel is passed in.

dopplershift · 2018-05-02T00:49:08Z

metpy/calc/thermo.py

+    dewpoint = dewpoint[sort_inds]
+
+    # Trim data to only top height and below as well as bottom height and above
+    pressure, temperature, dewpoint = get_layer(pressure, temperature, dewpoint,


This call of get_layer only differs from the one below with the passing of bottom. Are they both needed?

That was a try at something that won't survive 😄 I think I'm going to refactor some here - we don't want to trim before we interpolate a parcel.... hmmm.. more to come.

stickler-ci · 2018-05-02T15:53:29Z

metpy/calc/thermo.py

+
+        # Trim data to parcel starting point and below, interpolating the starting point
+        pressure, temperature, dewpoint = get_layer(pressure, temperature, dewpoint,
+                                                    depth=np.nanmax(pressure) * pressure.units - parcel_starting_pressure,


E501 line too long (122 > 95 characters)

stickler-ci · 2018-05-02T15:53:29Z

metpy/calc/thermo.py

+                                                    heights=heights)
+
+
+    # The user did not give us a parcel, so we'll calculate a sensible default.


E303 too many blank lines (2)

stickler-ci · 2018-05-02T15:53:29Z

metpy/calc/thermo.py

+
+        # Trim data to only top height and below as well as bottom height and above
+        pressure, temperature, dewpoint = get_layer(pressure, temperature, dewpoint,
+                                                    depth=np.nanmax(pressure) * pressure.units - top_pressure,


E501 line too long (110 > 95 characters)

stickler-ci · 2018-05-03T15:58:43Z

metpy/calc/tests/test_thermo.py

+                                                              parcel=custom_parcel)
+    dcape_truth = 101.56717405359117 * units.joule / units.kilogram
+    dcape_pressure_truth = np.array([973, 943.5, 925, 910.6, 878.4, 865, 850, 848, 847.2,
+                                     816.9, 793, 787.8, 759.6, 759, 732.2, 700, 670]) * units.hPa


E501 line too long (97 > 95 characters)

stickler-ci · 2018-05-03T15:58:44Z

metpy/calc/thermo.py

+
+        # Trim data to parcel starting point and below, interpolating the starting point
+        pressure, temperature = get_layer(pressure, temperature,
+                                          depth= profile_depth, heights=heights)


E251 unexpected spaces around keyword / parameter equals

stickler-ci · 2018-05-03T15:58:44Z

metpy/calc/thermo.py

+        # Trim data to be only above the bottom, interpolating if necessary. This must be done
+        # in separate step as there is no way to specify the top of a layer, just depth.
+        pressure, temperature = get_layer(pressure, temperature, bottom=bottom,
+                                          depth= profile_depth, heights=heights)


E251 unexpected spaces around keyword / parameter equals

kgoebber · 2018-07-09T21:40:20Z

So the RAOB program also calculates DCAPE and can do so in three different ways. It appears to do it via a lowest depth (e.g., 6 km) through either a density weighted average (most accurate), average wet-bulb, or coldest wet bulb (least accurate) [accuracy info from RAOB program]. Attached are two images using the coldest wet bulb temperature over the lowest 6 km from RAOB for the two times in the above examples from OUN for 17 April 2018 (ignore the month - its the same data). This gives different values from the NSHARP values given in the above figures - likely a different method.

kgoebber · 2018-07-09T21:43:49Z

Speaking of the NWS method (is this the NSHARP way?), I found the following PDF that talks about the DCAPE process (see slide number 6 DCAPE_Web.pdf).

To summarize the process:

From 700 mb (or anywhere 500-700 mb), determine the LCL.
Follow moist adiabat to surface from LCL found in 1.
DCAPE is the negative area (positive value) between the downdraft moist adiabat and the temperature profile.

jthielen · 2019-08-15T17:59:43Z

Are there any updates to the status of this, or what needs to be done before this can get merged? This would be very helpful for a couple ongoing projects in the research group I'm in.

dopplershift · 2019-08-15T19:19:30Z

@jthielen So we just need some help validating that what we're doing is actually correct. A scholarly source to cite for the method plus some good values to double check our work are what's needed.

mtesouro · 2022-08-19T09:34:15Z

I'm working in a proyect and I need the calculation of the Downdraft CAPE (DCAPE) and I'm testing this function and the other mentioned here. My surprise is that I found diferent results if I compared whith the data of the sounding.

I choose this sounding (https://www.spc.noaa.gov/exper/soundings/22081900_OBS/) and I realized the calculus whith the function downdraft_cape described in this post and the function created by jillianndufort and described in https://github.com/jillianndufort/Calculation-for-DCAPE

I found different results for the same data and differents of the result DCAPE in the sounding.

1.- This function downdraft_cape:
dcape = 117.76574757857342 delta_degree_Celsius * joule / kilogram
2.- The jillianndofort's function:
{'DD_method1': {'metpy': 41165.230535591356,
'Magnus': 0.0,
'Wexler': 0.0,
'Buck': 0.0},
'DD_method2': {'metpy': 473702.59788943676,
'Magnus': 2.241814634518002,
'Wexler': 2.2423655314996664,
'Buck': 2.242472299362524},
'DD_method3': {'metpy': -71.44700746827606,
'Magnus': 26.86878193998087,
'Wexler': nan,
'Buck': 29.057112541161665}}
3.- Sounding:
DCAPE = 983 j/KG

I don't understand what is happening because I think that the functions are OK in the sense of the programming.

I attached the data file so you can do the tests.

One last comment, in this downdraft cape function, I found a problem in the dcape.to('J/kg') conversion giving me an error:

DimensionalityError: Cannot convert from 'delta_degree_Celsius * joule / kilogram' ([length] ** 2 * [temperature] / [time] ** 2) to 'joule / kilogram' ([length] ** 2 / [time] ** 2)

Ignoring this, the result is the commented.
I have the same problem when I check this function whith the test_dcape_defaults. Whithout to('J/kg') it works fine.

Could you help me?

datos.txt

dopplershift · 2022-08-19T17:18:30Z

Thanks for kicking the tires on this calculation. Given that unit error, the implementation of the calculation is definitely not correct. Whether that's causing the difference in values, though, is unclear. Unfortunately, I don't have any cycles at the moment to dig into this.

mtesouro · 2022-08-22T09:41:37Z

I also think that they are two independent problems: the problem with the units and the calculus of the DCAPE. I'll try to check this these days, before my holidays. I think that it doesn't seem easy to solve.
If someone can have a look, will be welcome.
Thanks a lot.

dopplershift · 2023-11-14T23:32:42Z

Superseded by #3120.

jrleeman added the Area: Calc Pertains to calculations label Apr 24, 2018

jrleeman added this to the 0.8 milestone Apr 24, 2018

jrleeman requested a review from dopplershift as a code owner April 24, 2018 14:43

stickler-ci reviewed Apr 27, 2018

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dopplershift added the Type: Feature New functionality label May 1, 2018

Add downdraft CAPE calculation.

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refactor

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jrleeman force-pushed the DCAPE branch from 9f13554 to 5d46493 Compare May 2, 2018 15:53

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jrleeman added 4 commits May 2, 2018 15:10

dcape

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Add tests for DCAPE

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Refactor layer calculation

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Modify test for custom parcel

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jrleeman added 2 commits May 3, 2018 15:14

working on it

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refactor again

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jrleeman modified the milestones: 0.8, 0.9 May 4, 2018

update testing

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dopplershift modified the milestones: 0.9, 0.10 Jul 26, 2018

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Base automatically changed from master to main February 22, 2021 22:39

dopplershift requested a review from dcamron as a code owner February 22, 2021 22:39

dopplershift mentioned this pull request Jul 28, 2023

add downward cape #3120

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Add downdraft CAPE calculation #823

Add downdraft CAPE calculation #823

jrleeman commented Apr 24, 2018 •

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dopplershift commented Aug 19, 2022

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dopplershift commented Nov 14, 2023

		depth=pressure[-1] - top_pressure)


		# Calculate the difference in profile and environmental temperature to integrate

		heights=heights)


		# The user did not give us a parcel, so we'll calculate a sensible default.

Add downdraft CAPE calculation #823

Add downdraft CAPE calculation #823

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kgoebber commented Jul 9, 2018

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