.. note:: :class: sphx-glr-download-link-note Click :ref:`here ` to download the full example code .. rst-class:: sphx-glr-example-title .. _sphx_glr_auto_examples_ltg_den_hk.py: Probabilistic Lightning Density Nowcast (Hong Kong) ======================================================== This example demonstrates how to perform probabilistic lightning nowcast by advecting lightning density, using data from Hong Kong. Definitions -------------------------------------------------------- Import all required modules and methods: .. code-block:: python # Python package to allow system command line functions import os # Python package to manage warning message import warnings # Python package for time calculations import pandas as pd # Python package for numerical calculations import numpy as np # Python package for xarrays to read and handle netcdf data import xarray as xr # Python package for text formatting import textwrap # Python package for projection description import pyproj from pyresample import get_area_def # Python package for projection import cartopy.crs as ccrs # Python package for land/sea features import cartopy.feature as cfeature # Python package for reading map shape file import cartopy.io.shapereader as shpreader # Python package for creating plots from matplotlib import pyplot as plt # Python package for output grid format from matplotlib.gridspec import GridSpec # Python package for colorbars from matplotlib.colors import BoundaryNorm, ListedColormap from matplotlib.cm import ScalarMappable # Python com-swirls package to calculate motion field (rover) and semi-lagrangian advection from swirlspy.qpf import rover, sla # swirlspy data parser function from swirlspy.rad.iris import read_iris_grid # swirlspy test data source locat utils function from swirlspy.qpe.utils import timestamps_ending, locate_file # swirlspy regrid function from swirlspy.core.resample import grid_resample # swirlspy lightning function from swirlspy.obs import Lightning from swirlspy.ltg.map import gen_ltg_density # swirlspy standardize data function from swirlspy.utils import standardize_attr, FrameType # directory constants from swirlspy.tests.samples import DATA_DIR from swirlspy.tests.outputs import OUTPUT_DIR warnings.filterwarnings("ignore") plt.switch_backend('agg') Initialising ------------------------------------------------------------------------- Define the target grid: .. code-block:: python # Defining target grid area_id = "hk1980_250km" description = ("A 1km resolution rectangular grid " "centred at HKO and extending to 250 km " "in each direction in HK1980 easting/northing coordinates") proj_id = 'hk1980' projection = ('+proj=tmerc +lat_0=22.31213333333334 ' '+lon_0=114.1785555555556 +k=1 +x_0=836694.05 ' '+y_0=819069.8 +ellps=intl +towgs84=-162.619,-276.959,' '-161.764,0.067753,-2.24365,-1.15883,-1.09425 +units=m ' '+no_defs') x_size = 500 y_size = 500 area_extent = (587000, 569000, 1087000, 1069000) area_def = get_area_def( area_id, description, proj_id, projection, x_size, y_size, area_extent ) Define basemap: .. code-block:: python # Load the shape of Hong Kong map_shape_file = os.path.abspath(os.path.join( DATA_DIR, 'shape/hk_hk1980' )) # coastline and province map_with_province = cfeature.ShapelyFeature( list(shpreader.Reader(map_shape_file).geometries()), area_def.to_cartopy_crs() ) # define the plot function def plot_base(ax: plt.Axes, extents: list, crs: ccrs.Projection): # fake the ocean color ax.imshow( np.tile(np.array([[[178, 208, 254]]], dtype=np.uint8), [2, 2, 1]), origin='upper', transform=crs, extent=extents, zorder=-1 ) # coastline, province and state, color ax.add_feature( map_with_province, facecolor=cfeature.COLORS['land'], edgecolor='none', zorder=0 ) # overlay coastline, province and state without color ax.add_feature( map_with_province, facecolor='none', edgecolor='gray', linewidth=0.5 ) ax.set_title('') Defining a basetime, nowcast interval and nowcast duration: .. code-block:: python basetime = pd.Timestamp('201904201200').floor('min') basetime_str = basetime.strftime('%Y%m%d%H%M') nowcast_interval = pd.Timedelta(30, 'm') nowcast_duration = pd.Timedelta(2, 'h') Loading Lightning and Radar Data -------------------------------------------------------------------------- Extract Lightning Location Information System (LLIS) files to read. .. code-block:: python # The interval between LLIS files llis_file_interval = pd.Timedelta(1, 'm') # Finding the string representation # of timestamps marking the relevant LLIS files timestamps = timestamps_ending( basetime, duration=nowcast_interval, interval=llis_file_interval, format='%Y%m%d%H%M' ) # Locating files llis_dir = os.path.join(DATA_DIR, 'llis') located_files = [] for timestamp in timestamps: located_file = locate_file(llis_dir, timestamp) located_files.append(located_file) if located_file is not None: print(f"LLIS file for {timestamp} has been located") .. rst-class:: sphx-glr-script-out Out: .. code-block:: none LLIS file for 201904201130 has been located LLIS file for 201904201131 has been located LLIS file for 201904201132 has been located LLIS file for 201904201133 has been located LLIS file for 201904201134 has been located LLIS file for 201904201135 has been located LLIS file for 201904201136 has been located LLIS file for 201904201137 has been located LLIS file for 201904201138 has been located LLIS file for 201904201139 has been located LLIS file for 201904201140 has been located LLIS file for 201904201141 has been located LLIS file for 201904201142 has been located LLIS file for 201904201143 has been located LLIS file for 201904201144 has been located LLIS file for 201904201145 has been located LLIS file for 201904201146 has been located LLIS file for 201904201147 has been located LLIS file for 201904201148 has been located LLIS file for 201904201149 has been located LLIS file for 201904201150 has been located LLIS file for 201904201151 has been located LLIS file for 201904201152 has been located LLIS file for 201904201153 has been located LLIS file for 201904201154 has been located LLIS file for 201904201155 has been located LLIS file for 201904201156 has been located LLIS file for 201904201157 has been located LLIS file for 201904201158 has been located LLIS file for 201904201159 has been located Read data from files into Lightning objects. .. code-block:: python # Initialising Lightning objects # Coordinates are geodetic ltg_object_geodetic = Lightning( located_files, 'geodetic', basetime - nowcast_interval, basetime ) Locating IRIS REF radar files needed to generate motion field. The IRIS REF files are marked by start time. .. code-block:: python # The interval between the radar files rad_interval = pd.Timedelta(6, 'm') # Finding the string representation # of the timestamps # marking the required files # In this case, the most recent radar files # separated by `nowcast_interval` is required rad_timestamps = timestamps_ending( basetime, duration=nowcast_interval + rad_interval, interval=rad_interval ) rad_timestamps = [rad_timestamps[0], rad_timestamps[-1]] rad_dir = os.path.join(DATA_DIR, 'iris') located_rad_files = [] for timestamp in rad_timestamps: located_file = locate_file(rad_dir, timestamp) located_rad_files.append(located_file) if located_file is not None: print(f"IRIS REF file for {timestamp} has been located") .. rst-class:: sphx-glr-script-out Out: .. code-block:: none IRIS REF file for 1904201124 has been located IRIS REF file for 1904201154 has been located Read from iris radar files using read_iris_grid(). The data is in the Azimuthal Equidistant Projection. .. code-block:: python reflec_unproj_list = [] for file in located_rad_files: reflec = read_iris_grid(file) reflec_unproj_list.append(reflec) Data Reprojection --------------------------------------------------------------------------- Since the coordinates of the Lightning objects are geodetic, a conversion from geodetic coordinates to that of the user-defined projection system is required. This can be achieved by `swirlspy.obs.Lightning.reproject()` .. code-block:: python # pyproj representation of the map projection of the input data inProj = pyproj.Proj(init='epsg:4326') # pyproj representation of the intended map projection outProj = pyproj.Proj(area_def.proj_str) # reproject ltg_object = ltg_object_geodetic.reproject(inProj, outProj, 'HK1980') Radar data also needs to be reprojected from Azimuthal Equidistant to HK1980. This is achieved by the `swirlspy.core.resample` function. Following reprojection, the individual xarray.DataArrays can be concatenated to a single xarray.DataArrays. .. code-block:: python reflec_list = [] for z in reflec_unproj_list: reflec = grid_resample( z, z.attrs['area_def'], area_def, coord_label=['easting', 'northing'] ) reflec_list.append(reflec) reflectivity = xr.concat(reflec_list, dim='time') standardize_attr(reflectivity, frame_type=FrameType.dBZ) print(reflectivity) .. rst-class:: sphx-glr-script-out Out: .. code-block:: none array([[[nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], ..., [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan]], [[nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], ..., [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan]]]) Coordinates: * time (time) datetime64[ns] 2019-04-20T11:24:00 2019-04-20T11:54:00 * northing (northing) float64 1.068e+06 1.068e+06 ... 5.705e+05 5.695e+05 * easting (easting) float64 5.875e+05 5.885e+05 ... 1.086e+06 1.086e+06 Attributes: long_name: Reflectivity units: dBZ projection: hk1980 site: (114.12333341315389, 22.41166664287448, 580) radar_height: 8 area_def: Area ID: hk1980_250km\nDescription: A 1km resolution recta... proj_site: (830755.3393923986, 830262.1449904075) step_size: 0 days 00:30:00 zero_value: nan frame_type: FrameType.dBZ Generating lightning density field ------------------------------------------------------------------ Generate a lightning density field. #. Count the number of lightning strikes in a circular search area of 8km surrounding a pixel over the past 30 minutes. Do this for all the pixels. #. This value is then spatially and temporally averaged to give a lightning density, an indicator of lightning activity given as the number of strikes/km\ :sup:`2`/hr. .. code-block:: python # Obtaining lightning density from lightning objects ltg_density = gen_ltg_density( ltg_object, area_def, ltg_object.start_time, ltg_object.end_time, tolerance=8000, coord_label=['easting', 'northing'] ) print(ltg_density) # Duplicating ltg_density along the time dimension # so that it can be advected. ltg_density1 = ltg_density.copy() ltg_density1.coords['time'] = [basetime - nowcast_interval] ltg_density_concat = xr.concat( [ltg_density1, ltg_density], dim='time' ) # Identifying zero value ltg_density_concat.attrs['zero_value'] = np.nan .. rst-class:: sphx-glr-script-out Out: .. code-block:: none array([[[0., 0., 0., ..., 0., 0., 0.], [0., 0., 0., ..., 0., 0., 0.], [0., 0., 0., ..., 0., 0., 0.], ..., [0., 0., 0., ..., 0., 0., 0.], [0., 0., 0., ..., 0., 0., 0.], [0., 0., 0., ..., 0., 0., 0.]]]) Coordinates: * time (time) datetime64[ns] 2019-04-20T12:00:00 * northing (northing) float64 1.068e+06 1.068e+06 ... 5.705e+05 5.695e+05 * easting (easting) float64 5.875e+05 5.885e+05 ... 1.086e+06 1.086e+06 Attributes: long_name: Lightning density units: strikes/$km^2$/h Generating motion fields and extrapolating -------------------------------------------------------------- #. Generate motion field using ROVER. #. Extrapolate lightning density using the motion field by Semi-Lagrangian Advection. #. Repeat using different parameters to form an ensemble. .. code-block:: python # Different ROVER parameters params = pd.DataFrame() params['smallest_scale'] = [1, 1, 1, 2] params['largest_scale'] = [7, 7, 7, 7] params['rho'] = [9, 9, 9, 9] params['alpha'] = [2000, 2000, 10000, 2000] params['sigma'] = [1.5, 2.5, 1.5, 2.5] params['tracking_interval'] = [30, 30, 30, 30] xtrp_frames = [] for i in range(len(params)): # Generating motion field using ROVER motion = rover( reflectivity, start_level=params['smallest_scale'][i], max_level=params['largest_scale'][i], rho=params['rho'][i], alpha=params['alpha'][i], sigma=params['sigma'][i] ) # SLA steps = int(nowcast_duration.total_seconds() // nowcast_interval.total_seconds()) ltg_density_xtrp = sla(ltg_density_concat, motion, nowcast_steps=steps) xtrp_frames.append(ltg_density_xtrp) # Create coordinates for `ensemble` dimension ens_coords = ["Member-{:02}".format(i) for i in range(len(xtrp_frames))] # Concat ltg_frames along the ensemble dimension ltg_frames = xr.concat(xtrp_frames, pd.Index(ens_coords, name='ensemble')) print(ltg_frames) .. rst-class:: sphx-glr-script-out Out: .. code-block:: none RUNNING 'rover' FOR EXTRAPOLATION..... RUNNING 'rover' FOR EXTRAPOLATION..... RUNNING 'rover' FOR EXTRAPOLATION..... RUNNING 'rover' FOR EXTRAPOLATION..... array([[[[ 0., 0., 0., ..., 0., 0., 0.], [ 0., 0., 0., ..., 0., 0., 0.], [ 0., 0., 0., ..., 0., 0., 0.], ..., [ 0., 0., 0., ..., 0., 0., 0.], [ 0., 0., 0., ..., 0., 0., 0.], [ 0., 0., 0., ..., 0., 0., 0.]], [[nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], ..., [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan]], [[nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], ..., ... ..., [nan, nan, nan, ..., 0., nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan]], [[nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], ..., [nan, nan, nan, ..., 0., nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan]], [[nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan], ..., [nan, nan, nan, ..., 0., nan, nan], [nan, nan, nan, ..., nan, nan, nan], [nan, nan, nan, ..., nan, nan, nan]]]]) Coordinates: * time (time) datetime64[ns] 2019-04-20T12:00:00 ... 2019-04-20T14:00:00 * northing (northing) float64 1.068e+06 1.068e+06 ... 5.705e+05 5.695e+05 * easting (easting) float64 5.875e+05 5.885e+05 ... 1.086e+06 1.086e+06 * ensemble (ensemble) object 'Member-00' 'Member-01' 'Member-02' 'Member-03' Attributes: long_name: Lightning density units: strikes/$km^2$/h zero_value: nan Now, let us visualise the extrapolated lightning density fields for the next 30 minutes. .. code-block:: python levels = [ 0, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 999 ] cmap = ListedColormap([ '#FFFFFF', '#5050FF', '#00FFFF', '#00C030', '#A0FF80', '#FFFF40', '#FF9830', '#FF0000', '#FF80FF', '#800080' ]) norm = BoundaryNorm(levels, ncolors=cmap.N, clip=True) mappable = ScalarMappable(cmap=cmap, norm=norm) mappable.set_array([]) # Defining the crs crs = area_def.to_cartopy_crs() # Defining area x = ltg_frames.coords['easting'].values y = ltg_frames.coords['northing'].values extents = [ np.min(x), np.max(x), np.min(y), np.max(y) ] qx = motion.coords['easting'].values[::20] qy = motion.coords['northing'].values[::20] qu = motion.values[0, ::20, ::20] qv = motion.values[1, ::20, ::20] fig = plt.figure(figsize=(8, 8), frameon=False) gs = GridSpec( 2, 2, figure=fig, wspace=0.03, hspace=-0.25, top=0.95, bottom=0.05, left=0.17, right=0.845 ) # The time to visualise vis_time = basetime + nowcast_interval for i, mem in enumerate(ltg_frames.ensemble.values): row = i // 2 col = i % 2 ax = fig.add_subplot(gs[row, col], projection=crs) # plot base map plot_base(ax, extents, crs) # plot lightning frame = ltg_frames.sel(ensemble=mem, time=vis_time) frame.where(frame > levels[1]).plot( cmap=cmap, norm=norm, add_colorbar=False ) # plot motion vector ax.quiver( qx, qy, qu, qv, pivot='mid' ) ax.set_title(mem.split("-")[1], fontsize=10) ax.text( extents[0], extents[3], textwrap.dedent( """ Lightning Density Based @ {baseTime} """ ).format( baseTime=basetime.strftime('%H:%MH') ).strip(), fontsize=10, va='bottom', ha='left', linespacing=1 ) ax.text( extents[1], extents[3], textwrap.dedent( """ {validDate} Valid @ {validTime} """ ).format( validDate=basetime.strftime('%Y-%m-%d'), validTime=vis_time.strftime('%H:%MH') ).strip(), fontsize=10, va='bottom', ha='right', linespacing=1 ) cbar_ax = fig.add_axes([0.875, 0.125, 0.03, 0.75]) cbar = fig.colorbar( mappable, cax=cbar_ax, ticks=levels[:-1], extend='max', format='%.3g') cbar.ax.set_ylabel(ltg_frames.attrs['long_name'], rotation=90) fig.savefig( os.path.join(OUTPUT_DIR, "ltg-hk.png"), bbox_inches='tight' ) .. image:: /auto_examples/images/sphx_glr_ltg_den_hk_001.png :class: sphx-glr-single-img Deriving lightning probabilities ------------------------------------------------------------------------------ .. code-block:: python # Finally, it is possible to derive # the probability of lightning exceeding threshold from our ensemble forecast. # # Compute exceedance probabililities for a 1 strikes/km^2/h threshold P = (ltg_frames > 1).sum(dim='ensemble') / len(ltg_frames.ensemble) * 100 # Define cmap, norm levels = [ 0, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 ] cmap = plt.get_cmap("OrRd", len(levels)) norm = BoundaryNorm(levels, ncolors=cmap.N, clip=True) # Plotting the Exceedance Probability for the first 30 minutes nowcast fig = plt.figure(figsize=(15, 10)) ax = plt.axes(projection=area_def.to_cartopy_crs()) plot_base(ax, extents, area_def.to_cartopy_crs()) P.where(P > levels[0]).sel(time=vis_time).plot( cmap=cmap, norm=norm ) ax.text( extents[0], extents[3], textwrap.dedent( """ Probability exceeding 1 strikes/$km^2$/hr Based @ {baseTime} """ ).format( baseTime=basetime.strftime('%H:%MH') ).strip(), fontsize=20, va='bottom', ha='left', linespacing=1 ) ax.text( extents[1], extents[3], textwrap.dedent( """ {validDate} Valid @ {validTime} """ ).format( validDate=basetime.strftime('%Y-%m-%d'), validTime=vis_time.strftime('%H:%MH') ).strip(), fontsize=20, va='bottom', ha='right', linespacing=1 ) ax.set_title("") fig.savefig( os.path.join(OUTPUT_DIR, "ltg-hk-p.png"), bbox_inches='tight' ) .. image:: /auto_examples/images/sphx_glr_ltg_den_hk_002.png :class: sphx-glr-single-img **Total running time of the script:** ( 0 minutes 50.326 seconds) .. _sphx_glr_download_auto_examples_ltg_den_hk.py: .. only :: html .. container:: sphx-glr-footer :class: sphx-glr-footer-example .. container:: sphx-glr-download :download:`Download Python source code: ltg_den_hk.py ` .. container:: sphx-glr-download :download:`Download Jupyter notebook: ltg_den_hk.ipynb ` .. only:: html .. rst-class:: sphx-glr-signature `Gallery generated by Sphinx-Gallery `_