Dual-Pol Radarfirst Lab Exercise

Dual-Pol RadarFirst Lab Exercise

Possible Uses of Dual-Pol Radar Data for Emergency Management

Objective:

This exercise serves as a first introduction to using dual-pol radar data. In the lab, you will look at several different storms and dual-pol products during the April 14, 2012 supercell event. The examples illustrate several potential applications of dual-pol data in emergency management.

Remember that there is a significant learning curve with dual-pol and that not everyone will find it to be useful. Repeated exposure, lots of practice, and patience will be key for those who want to incorporate dual-pol into their decision making.

Instructions:

You will need to use the latest version of RadarFirst to complete this lab. Please read through the questions contained in this lab exercise and answer them as best you can in the space provided on each page.

You are welcome (and encouraged!) to work with others in class, but each person will need to work with the data on their screen and answer the questions in the lab. Once everyone is finished we will walk through the lab questions together and discuss them.

Region of Focus for this Lab (blue shaded region):

1 Terminology:

The following are definitions of several terms you may see during this lab:

• Base Reflectivity (BREF) – radar product that measures how much of the radar’s energy is reflected back to the radar. More particles and/or bigger particles reflect more energy. This is the most common radar product shown on TV.

• Correlation Coefficient (CC) – dual-pol radar product that measures how uniform or diverse radar targets are. Primary applications of this product including: 1) distinguishing between weather and non-weather echoes, 2) identifying hail spikes, 3) identifying tornadic debris, and 4) identifying the melting layer.

• Differential Reflectivity (ZDR) – dual-pol radar product that measures the shape of radar targets. Primary applications of this product include: 1) identifying hail, 2) identifying heavy rain, and 3) identifying the melting layer.

• Hook Echo – a feature observed in Base Reflectivity in the near-surface levels of the inflow region of a supercell thunderstorm. A hook echo is not a guarantee of a tornado, but if a tornado occurs it is most common in this region.

• Hydrometeor Classification (HC) – a derived dual-pol radar product that provides the radar’s best guess of what the different radar echoes are.

• Precipitation Estimation – a collection of dual-pol radar products that estimate the amount of precipitation that has fallen in 1 hour (One Hour Accumulation – OHA, Digital Accumulation Array – DAA) or throughout the duration of a storm (Digital Storm Total Accumulation – DSA). Another product estimates how much rain is falling right now (Digital Precipitation Rate – DPR).

• Specific Differential Phase (KDP) – dual-pol radar product that measures how much the horizontal and vertical pulses slow down compared to each other. The primary application of this product is identifying heavy rain.

• Storm-Relative Velocity (SRVEL) – radar product that subtracts out general storm motion to provide only what is occurring within a thunderstorm. The only use of SRVEL is to diagnose if rotation is occurring and is most useful in situations where rotation is subtle and/or storms are moving quickly.

• Supercell Thunderstorm – a long-lived thunderstorm characterized by a rotating updraft. Supercells are the most prolific tornado producing storm type.

2 Lab Exercise:

Open RadarFirst. Put the software in 2-pane mode (View  Two Pane) and make cities visible (Edit  Options…  Show Cities). The tables provided in each question detail the settings you need to use in RadarFirst to answer that question. To change the date and time in RadarFirst, go to Edit  Date... at the top.

Question 1. What does the correlation coefficient (CC) product measure? Please explain.

Question 2. Radar Date Time Left Pane Right Pane CC1 BREF1 KVNX – Vance 4/14/2012 2:00PM (Correlation Coefficient 1) (Base Reflectivity 1) Focus on the tornado warned storm in southwest Kansas near the Oklahoma-Kansas border. Correlation coefficient values less than 0.8 are non-meteorological. Scroll your mouse over the storm and find where CC values are less than 0.8. What do we call this feature?

Question 3. Radar Date Time Left Pane Right Pane HC1 BREF1 KVNX – Vance 4/14/2012 2:00PM (Hydrometeor Classification 1) (Base Reflectivity 1) Keep focusing on the same storm. Scroll your mouse over the storm and watch the legend to see what the hydrometeor classification product says. Write down all the classifications you see (like RA, etc.) and define what each of them mean (for instance RA – Rain). Do you agree with all of them?

3 Question 4. What does the differential reflectivity (ZDR) product measure? Please explain.

Question 5. Radar Date Time Left Pane Right Pane ZDR1 BREF1 KVNX – Vance 4/14/2012 4:08PM (Differential Reflectivity 1) (Base Reflectivity 1) Shift your attention to northwest Oklahoma to the storm between Freedom and Fort Supply. Scroll over the highest reflectivity areas of the storm in the right pane – what are the corresponding Differential Reflectivity values in the left pane? What do you think that is telling us?

Question 6. Look at the same storm you did in question 5. Find the highest Differential Reflectivity values in the storm in the left pane. What do you think those are telling us?

Question 7. Radar Date Time Left Pane Right Pane HC1 BREF1 KVNX – Vance 4/14/2012 4:08PM (Hydrometeor Classification 1) (Base Reflectivity 1) Looking at the same storm scroll over the values in the left pane. What are the three primary Hydrometeor Classification values you see for this storm? How well do they compare with your answers on questions 5 and 6?

4 Question 8. Radar Date Time Left Pane Right Pane BREF1 CC1 (Base Reflectivity 1) KVNX – Vance 4/14/2012 8:00PM (Correlation Coefficient 1) & SRVEL1 (Storm-relative Vel.) Shift your attention to a storm west and north of Cherokee. In the right pane, mouse over the hook echo of the storm in BREF1 and feel free to switch to SRVEL 1 (Storm Relative Velocity 1) to see rotation. In the left pane can you spot a feature in the Correlation Coefficient product in the same area? Describe what you are seeing and provide a guess of what it might be.

Question 9. What is the primary use for the Specific Differential Phase (KDP) product?

Question 10. Radar Date Time Left Pane Right Pane KDP1 BREF1 KVNX – Vance 4/14/2012 8:28PM (Specific Differential Phase 1) (Base Reflectivity 1) Focusing on the supercell along the Oklahoma-Kansas border (southwest of Wichita, KS), where in the storm are the largest KDP values? What is KDP telling us?

Question 11. What other dual-pol products can be used for heavy precipitation? Write them down.