Task: Calculate Snowfall Retrievals from SAIL X-Band Radar

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Task: Calculate Snowfall Retrievals from SAIL X-Band Radar

import warnings warnings.simplefilter(“ignore”, UserWarning)

import glob import os import datetime

import numpy as np import matplotlib.pyplot as plt import pyart import xarray as xr from matplotlib.dates import DateFormatter

from metpy.plots import USCOUNTIES

import cartopy.crs as ccrs import cartopy.feature as cfeature

Radar Reflectivity - Snowfall (Z-S) Relationships

We setup helper functions to calculate the snowfall retrieval, using following notation:

\(Z = A*S ^ {B}\)

Where:

  • Z = Reflectivity in dBZ

  • A = Coefficient applied to Z-S Relationship (not in the exponent)

  • S = Liquid snowfall rate

  • B = Coefficient applied to Z-S Relationship (in the exponent)

We also need to apply a snow water equivalent ratio (swe) to convert from liquid to snow (ex. 8 inches of snow –> 1 inch of rain would be 8.0).

This equation now becomes:

\(Z = swe*A*S ^ {B}\)

Solving for S, we get:

\(S = swe * (\frac{z}{a})^{1/B}\)

Where z is reflectivity in units of dB (\(z =10^{Z/10}\))

Define our Z-S Relationships

We start by using the Z-S Relationships Described in Bukovčić et al. (2018), where we refer to following relationships in Table 1:

Source

Z(S) relation for dry snow

A Coefficient

B Coefficient

Radar Band

Wolfe and Snider (2012)

\(Z = {110}S^{2}\)

110

2

S

WSR-88D high plains

\(Z = {130}S^{2}\)

130

2

S

WSR-88D Intermountain West

\(Z = {40}S^{2}\)

40

2

S

Matrosov et al.(2009) Braham(1990)

\(Z = {67}S^{1.28}\)

67

1.28

X

Matrosov et al.(2009) Braham(1990)

\(Z = {114}S^{1.39}\)

114

1.39

X

Matrosov et al.(2009) Braham(1990)

\(Z = {136}S^{1.3}\)

136

1.3

X

Matrosov et al.(2009) Braham(1990)

\(Z = {28}S^{1.44}\)

28

1.44

X

Matrosov et al.(2009) Braham(1990)

\(Z = {36}S^{1.56}\)

36

1.56

X

Matrosov et al.(2009) Braham(1990)

\(Z = {48}S^{1.45}\)

48

1.45

X

Matrosov (1992)

\(Z = {410}S^{1.6}\)

410

1.6

X

Matrosov (1992)

\(Z = {340}S^{1.6}\)

340

1.75

X

Matrosov (1992)

\(Z = {240}S^{1.6}\)

240

1.95

X

Boucher and Wieler (1985)

\(Z = {229}S^{1.65}\)

229

1.65

X

Fujiyoshi et al. (1990)

\(Z = {427}S^{1.09}\)

427

1.09

X

Puhakka (1975)

\(Z = {1050}S^{2}\)

1050

2

X

Sekhon and Srivastava (1970)

\(Z = {1780}S^{2.21}\)

1780

2.21

X

List the Available Files

We will use files on the Oak Ridge Laboratory Computing Facility (ORLCF), within the shared SAIL directory /gpfs/wolf/atm124/proj-shared/sail.

These radar files have been merged from a single sweep in each file, to whole volume scans in each file.

file_list = sorted(glob.glob("/data/project/ARM_Summer_School_2024_Data/sail/radar/*"))

file_list[0:10]

['/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.000206.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.000726.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.001246.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.001806.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.002326.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.002846.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.003406.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.003926.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.004446.nc',
 '/data/project/ARM_Summer_School_2024_Data/sail/radar/gucxprecipradarcmacS2.c1.20220310.005006.nc']

Your Turn!

Question 1 - Easy

Using material presented this week, apply one of the above relationships to SAIL X-Band radar file and display

Question 2 - Intermediate

Using the above methodology, calculate the snowfall accumulation for an hour (or day)

Question 3 - Hard

Compare this hourly (or daily) accumulation to WRF output for the same day

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