Lab 12.1 – Ash plume Moves over the Endurance Array
Fundamental concept: Describe variations in atmospheric conditions indicative of wildfire ash plumes and identify the arrival date/time of the plume over the Endurance Array.
Estimated time to complete: 20-30 minutes
Data skills Preparation: Lab 2
Materials needed: None
In this activity you will examine data during the passage of the 2020 Labor Day Fire’s ash plume over the OOI Endurance Array. Again, think about your experiences around a campfire. What would the air above the Endurance Array be like within the smoke plume? In this lab section, you will determine the arrival date of the smoke plume based on physical characteristics of the air above the array, observed by the Bulk Meteorology Package on the Oregon Offshore Surface Mooring.
Key Parameters
Wind Speed and Direction
Winds at the latitude of the Endurance Array commonly blow from west to east. However, during the period when the smoke plume drifted over the Endurance array, the winds temporarily shifted and east winds prevailed for a period, meaning that the winds were coming from the east and pushing the plume toward the west, out to sea.
For the purposes of this lab, we will examine “eastward wind” velocity which is the same as “west wind” velocity, meaning that the wind is moving from west to east. The eastward wind velocity can be positive or negative: positive values indicate wind blowing from the west to the east, while negative values indicate wind blowing from the east to the west. For example:
- +5 m/s on the graph in Figure 12.1.1 means wind is moving from west toward east at 5 meters per second
- -5 m/s on the graph means wind is moving from east toward west at 5 meters per second
Figure 12.1.1. Eastward wind speed measured at the OOI Endurance Array Oregon Shelf Surface Mooring during the 2020 Labor Day Fire.
Do you need help remembering the various ways to refer to wind velocity? If so, click here to go to Lab 2.5 for a refresher.
Air Temperature
Air temperature is the measure of the warmth or coolness of the air in the atmosphere. It is a fundamental aspect of weather and plays a crucial role in shaping our climate and environment. Although air temperature is affected by a number of factors, including solar radiation, latitude, altitude, time of day, and seasonal changes, smoke plumes can increase the temperatures by absorbing sunlight and emitting the absorbed energy as heat.
Figure 12.1.2. Time series of air temperature.
Relative Humidity
Relative humidity (RH) is the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature. The warmer the air, the more water vapor it can hold. For example, given the same amount of water vapor in an air mass, relative humidity would be higher in cooler air and lower in warmer air. Wildfires are more likely to burn in lower relative humidity because the air dries out vegetation that fuels the fire.
Figure 12.1.3. Time series of relative humidity.
Net Shortwave Irradiance
Net shortwave irradiance (NETSIRR) is a measure of solar radiant energy in the visible and near-ultraviolet wavelengths less any outgoing (upward) short-wave radiation from the ocean surface. Net shortwave irradiance increases during the daytime and decreases at night. It is also impacted by particles in smoke plumes, which scatter light and reduce the amount of solar radiation that reaches the surface of the ocean.
Figure 12.1.4. Time series of net shortwave irradiance.
Quick Check Questions
Click on the graphs to expand to a larger window.
Interpretation Questions
Use the interactive graphs in Figure 12.1.5 to answer questions 1-7 below:
Figure 12.1.5. Interactive time series graphs from the OOI Oregon Shelf Surface Mooring in September, 2020. Use the drop down menus to select parameters to include in Graph 1 and Graph 2. Use the “Zoom to” buttons or the slider bars between the graphs to zoom in and out.
- Select “Eastward Wind” for Graph 1 in Figure 12.1.5. On what date does the wind shift to its maximum westward velocity?
- Now select “Air Temperature” as the parameter for Graph 2. How does the air temperature change at the time of the wind shift? Quantify the change in degrees from the day before to the time of the wind shift.
- Select “Relative Humidity” for Graph 2, and compare the two graphs. Does there appear to be a change in relative humidity corresponding to the change in eastward winds? If so, what change occurs?
- Select net shortwave irradiance in Graph 2. Does the net shortwave radiation decrease or increase at the time of the strongest westward wind?
- Based on all the parameters explored above, on what date did the smoke plume arrive over the array?
Application Questions
- Based on the net shortwave irradiance data in Figure 12.1.5, on which day was the smoke plume the most dense over the array?
- What do you think caused the observed change in relative humidity over the Endurance Array as the smoke plume arrived? Consider the properties of smoke—how it absorbs and emits light and heat energy, and how these factors could influence temperature and, consequently, relative humidity.
- Watch the GOES satellite video below and stop it when you see the smoke plume arrive along the coast of Oregon. Record the date and time that the smoke plume, driven by the atypical east winds, first arrives at the coast of Oregon and above the Endurance Array. Does the GOES video confirm the date you estimated based on evidence observed on the arrays bulk meteorology package? Explain your answer by including the date of the smoke plume’s arrival using both the parameters explored above and the GOES satellite video.
GOES Satellite Imaging: The GOES satellite has a suite of imaging instruments including visible, near infrared, and infrared wavelengths. This allows the satellite to image during both daylight and darkness, and to indicate various elements at Earth’s surface or in the atmosphere, such as trees, water, clouds, moisture or smoke.
