params#

Convective#

template<typename Lifter>
PressureLayer sharp::effective_inflow_layer(Lifter &lifter, const float pressure[], const float height[], const float temperature[], const float dewpoint[], const float virtemp_arr[], float pcl_vtmpk_arr[], float buoy_arr[], const std::ptrdiff_t N, const float cape_thresh = 100.0, const float cinh_thresh = -250.0, Parcel *mupcl = nullptr)#

Computes the Effective Inflow Layer for a given atmospheric sounding.

Author

Kelton Halbert - NWS Storm Prediction Center

Computes the Effective Inflow Layer, or the layer of the atmosphere believed to be the primary source of inflow for supercell thunderstorms. The Effective Inflow Layer, and its use in computing shear and storm relative helicity, is described by Thompson et al. 2007: https://www.spc.noaa.gov/publications/thompson/effective.pdf

Standard/default values for cape_thresh and cinh_thresh have been experimentally determined to be cape_thresh = 100 J/kg and cinh_thresh = -250 J/kg. If a pointer to a parcel object is passed as the last arguments, the most ustanble parcel found during the EIL search will be returned to that pointer.

All arrays are treated as inputs (and expected to be precomputed) except for the buoyancy array. It is more accurately meant to be an empty buffer array that can be used to hold buoyancy values during parcel lifting and integration.

Parameters:

  • lifter – (parcel lifting functor)

  • pressure – (Pa)

  • height – (meters)

  • temperature – (K)

  • dewpoint – (K)

  • virtemp_arr – (K)

  • pcl_vtmpk_arr – (K)

  • buoy_arr – (m/s^2)

  • N – (length of arrays)

  • cape_thresh – (J/kg; default=100.0)

  • cinh_thresh – (J/kg; default=-250.0)

  • mupcl – (store the most unstable parcel; defualt=nullptr)

Returns:

{bottom, top}

PressureLayer sharp::effective_inflow_layer(sharp::lifter_wobus &lifter, const float pressure[], const float height[], const float temperature[], const float dewpoint[], const float virtemp_arr[], float pcl_vtmpk_arr[], float buoy_arr[], const std::ptrdiff_t N, const float cape_thresh, const float cinh_thresh, Parcel *mupcl)#
PressureLayer sharp::effective_inflow_layer(sharp::lifter_cm1 &lifter, const float pressure[], const float height[], const float temperature[], const float dewpoint[], const float virtemp_arr[], float pcl_vtmpk_arr[], float buoy_arr[], const std::ptrdiff_t N, const float cape_thresh, const float cinh_thresh, Parcel *mupcl)#
WindComponents sharp::storm_motion_bunkers(const float pressure[], const float height[], const float u_wind[], const float v_wind[], const std::ptrdiff_t N, HeightLayer mean_wind_layer_agl, HeightLayer wind_shear_layer_agl, const bool leftMover = false, const bool pressureWeighted = false)#

Estimates supercell storm motion using the Bunkers et al. 2000 method.

Author

Kelton Halbert - NWS Storm Prediction Center

Estimates supercell storm motion using the Bunkers et al. 2000 method described in the following paper: https://doi.org/10.1175/1520-0434(2000)015%3C0061:PSMUAN%3E2.0.CO;2

This does not use any of the updated methods described by Bunkers et al. 2014, which uses Effective Inflow Layer metricks to get better estimates of storm motion, especially when considering elevated convection.

Parameters:

  • pressure – (Pa)

  • height – (meters)

  • u_wind – (m/s)

  • v_wind – (m/s)

  • N – (length of arrays)

  • mean_wind_layer_agl – {bottom, top}

  • wind_shear_layer_agl – {bottom, top}

  • leftMover – (default=false)

  • pressureWeighted – (default=false)

Returns:

{storm_u, storm_v}

WindComponents sharp::storm_motion_bunkers(const float pressure[], const float height[], const float u_wind[], const float v_wind[], const std::ptrdiff_t N, PressureLayer eff_infl_lyr, const Parcel &mupcl, const bool leftMover = false)#

Estimates supercell storm motion by using the Bunkers et al. 2014 method.

Author

Kelton Halbert - NWS Storm Prediction Center

Estimates supercell storm motion using the Bunkers et al. 2014 method described in the following paper: http://dx.doi.org/10.15191/nwajom.2014.0211

This method is parcel based, using a mean-wind vector defined as the pressure-weighted mean wind between the Effective Inflow Layer surface (see sharp::effective_inflow_layer) and 65% of the depth between that surface and the most-unstable parcel’s Equilibrium Level. This method produces the same storm motion estimate for surface based supercells, and captures the motion of elevated supercells much better than the Bunkers 2000 method.

The input parameters eff_infl_lyr and mupcl (effective inflow layer bounds and the most unstable parcel, respectively) are required to be be precomputed and passed to this routine. These are expensive operations that are presumed to be computed at some other point in the analysis pipeline, so just pass those variables here.

Parameters:

  • pressure – (Pa)

  • height – (meters)

  • u_wind – (m/s)

  • v_wind – (m/s)

  • N – (length of arrays)

  • eff_infl_lyr – {bottom, top}

  • mupcl – (Precomputed parcel)

  • leftMover – (default=false)

Returns:

{storm_u, storm_v}

std::pair<WindComponents, WindComponents> sharp::mcs_motion_corfidi(const float pressure[], const float height[], const float u_wind[], const float v_wind[], const std::ptrdiff_t N)#

Compute the Corfidi upshear and downshear MCS motion vectors.

Author

Kelton Halbert - NWS Storm Prediction Center

Estimates mesoscale convective system (MCS) motion vectors for upshear and downshear propagating convective systems as in Corfidi et al. 2003. The method is based on observations that MCS motion is a function of 1) the advection of existing cells by the mean wind and 2) the propagation of new convection relative to existing storms.

https://www.spc.noaa.gov/publications/corfidi/mcs2003.pdf

Parameters:

  • pressure – (Pa)

  • height – (meters)

  • u_wind – (m/s)

  • v_wind – (m/s)

  • N – (length of arrays)

Returns:

{upshear, downshear}

WindComponents sharp::effective_bulk_wind_difference(const float pressure[], const float hght[], const float u_wind[], const float v_wind[], const std::ptrdiff_t N, sharp::PressureLayer effective_inflow_lyr, const float equilibrium_level_pressure)#

Compute the Effective Bulk Wind Difference.

Author

Kelton Halbert - NWS Storm Prediction Center

The effective bulk wind difference is the wind shear between the bottom height of the effective inflow layer, and 50% of the equilibrium level depth. This is analogous to the usage of 0-6 km wind shear, but allows more flexibility for elevated convection. Returns sharp::MISSING if the effective inflow layer or equilibrium level pressure are sharp::MISSING.

Parameters:

  • pressure – (Pa)

  • height – (meters)

  • u_wind – (m/s)

  • v_wind – (m/s)

  • N – length of arrays

  • effective_inflow_lyr – {bottom, top}

  • equilibrium_level_pressure – (Pa)

Returns:

Effective Bulk Wind Differce (m/s)

float sharp::energy_helicity_index(float cape, float helicity)#

Compute the Energy Helicity Index.

Author

Kelton Halbert - NWS Storm Prediciton Center

EHI is a composite parameter based on the premise that storm rotation should be maximized when CAPE is large and SRH is large. Typically, the layers used for helicity are either 0-1 km or 0-3 km.

https://doi.org/10.1175/1520-0434(2003)18%3C530:RSATFP%3E2.0.CO;2

Parameters:

  • cape – Convective Available Potential Energy (J/kg)

  • helicity – Storm Relative Helicity (m^2/s^2)

Returns:

EHI (unitless)

float sharp::supercell_composite_parameter(float mu_cape, float eff_srh, float eff_shear)#

Compute the Supercell Composite Parameter.

Author

Kelton Halbert - NWS Storm Prediciton Center

The supercell composite parameter is used to diagnose environments where supercells are favored. Requires computing most unstable CAPE, effective layer storm relative helicity, and effective bulk shear. Effective bulk shear is the vector difference between the winds at the bottom of the effective inflow layer, and 50% of the equilibrium level height. It is similar to the 0-6 km shear vector, but allows for elevated supercell thunderstorms.

The left-moving supercell composite parameter can be computed by providing effective SRH calculated using the bunkers left-moving storm motion, and will return negative values.

References: Thompson et al 2003: https://www.spc.noaa.gov/publications/thompson/ruc_waf.pdf

Thompson et al 2007: https://www.spc.noaa.gov/publications/thompson/effective.pdf

Thompson et al 2012: https://www.spc.noaa.gov/publications/thompson/waf-env.pdf

Parameters:

  • mu_cape – Most Unstable CAPE (J/kg)

  • eff_srh – Effective Layer SRH (m^2/s^2)

  • eff_shear – Effective Bulk Shear (m/s)

Returns:

SCP

float sharp::significant_tornado_parameter(Parcel pcl, float lcl_hght_agl, float storm_relative_helicity, float bulk_wind_difference)#

Compute the Significant Tornado Parameter.

Author

Kelton Halbert - NWS Storm Prediction Center

The Significant Tornado Parameter is used to diagnose environments where tornadoes are favored. STP traditionally comes in two flavors: fixed-layer, and effective-layer. Fixed-layer STP expects surface-based CAPE, the surface-based LCL, 0-1 km storm-relative helicity, the 0-6 km bulk wind difference, and the surface-based CINH. For the effective inflow layer based STP, use 100mb mixed-layer CAPE, 100mb mixed-layer LCL height AGL, effective-layer srh, the effective layer bulk wind difference, and the 100mb mixed-layer CINH. NOTE: The effective bulk wind difference is the shear between the bottom of the effective inflow layer and 50% of the height of the equilibrium level of the most unstable parcel.

References: Thompson et al 2012: https://www.spc.noaa.gov/publications/thompson/waf-env.pdf

Parameters:

  • pcl – a sharp::Parcel

  • lcl_hght_agl – The height of the LCL (meters AGL)

  • storm_relative_helicity – Right-moving supercell SRH (m^2/s^2)

  • bulk_wind_difference – (m/s)

Returns:

STP

float sharp::significant_hail_parameter(const sharp::Parcel &mu_pcl, float lapse_rate_700_500mb, float tmpk_500mb, float freezing_lvl_agl, float shear_0_6km)#

compute the Significant Hail Parameter

Author

Kelton Halbert - NWS Storm Prediction Center

Compute the Significant Hail Parameter, which was developed to delineate between significant (>=2” diameter) and non-significant

(<2” diameter) hail environments.

The 0-6 km shear is confined to a range of 7-27 m/s, mixing ratio is confined to a range of 11-13.6 g/kg, and the 500mb temperature maximum is capped at -5.5C.

After an initial calculation of SHIP, it undergoes the following modifications: 1) if MUCAPE < 1300 J/kg, SHIP = SHIP * (MUCAPE/1300) 2) if 700-500 mb lapse rate < 5.8 C/km, SHIP = SHIP * (lr75/5.8) 3) if the freezing level < 2400 m AGL, SHIP = SHIP * (fzl/2400)

It is important to note the SHIP is NOT a forecast hail size. Values of SHIP greater than 1 indicate a favorable environment for significant hail, and values greater than 4 are considered very high.

Parameters:

  • mu_pcl – sharp::Parcel:most_unstable_parcel

  • lapse_rate_700_500mb – (K/km)

  • tmpk_500mb – (K)

  • freezing_lvl_agl – (meters)

  • shear_0_6km – (m/s)

Returns:

Significant Hail Parameter

PressureLayer sharp::hail_growth_layer(const float pressure[], const float temperature[], const std::ptrdiff_t N)#

Get the layer encompassing the lowest hail growth zone (-10 to -30 C)

Author

Kelton Halbert - NWS Storm Prediction Center

Search for and return the sharp::PressuerLayer of the lowest altitude hail growth zone. If none is found, the top and bottom pressure levels are set to sharp::MISSING.

Parameters:

  • pressure – (Pa)

  • temperature – (K)

  • N – (length of arrays)

Returns:

The top and bottom of the hail growth zone (Pa)

float sharp::precipitable_water(PressureLayer layer, const float pressure[], const float mixing_ratio[], const std::ptrdiff_t N)#

Computes the precipitable water vapor content over a layer.

Author

Kelton Halbert - NWS Storm Prediction Center

Given a sharp::PressureLayer to integrate over, compute the preciptable water from the given pressure and mixing ratio arrays.

Parameters:

  • layer – (Pa)

  • pressure – (Pa)

  • mixing_ratio – (unitless)

  • N – (length of arrays)

Returns:

precipitable water (mm)

Fire#

float sharp::equilibrium_moisture_content(float temperature, float rel_humidity)#

Computes the equilibrium moisture content for fuel.

Author

Kelton Halber - NSW Storm Prediction Center

Compute the equilibrium moisture content for fuel as in Simard (1968).

Parameters:

  • temperature – (K)

  • rel_humidity – (fraction)

Returns:

EMC (fraction)

float sharp::fosberg_fire_index(float temperature, float rel_humidity, float wind_speed)#

Compute the Fosberg fire-weather index.

Author

Kelton Halbert - NWS Storm Prediction Center

Compute the Fosberg Fire-Weather Index (FWWI) as in Fosberg (1978).

Parameters:

  • temperature – (K)

  • rel_humidity – (fraction, unitless)

  • wind_speed – (m/s)

Returns:

Fosberg Fire-Weather Index

Winter#

PressureLayer sharp::dendritic_layer(const float pressure[], const float temperature[], const std::ptrdiff_t N)#

Get the layer encompassing the lowest dendritic growth zone (-12 to -17 C)

Author

Kelton Halbert - NWS Storm Prediction Center

Search for and return the sharp::PressuerLayer of the lowest altitude dendritic growth zone. If none is found, the top and bottom pressure levels are set to sharp::MISSING.

Parameters:

  • pressure – (Pa)

  • temperature – (K)

  • N – (length of arrays)

Returns:

The top and bottom of the dendritic growth zone (Pa)