Operational tool for global near-real time detection and tracking of wildfire smoKe plUMes in the upper troposphere and lower strAtospheRe

(Oper-KUMAR)

 Purpose

The Oper-KUMAR tool is intended for operational near-real time (NRT) analysis and visualization of satellite observations of wildfire smoke plumes in the upper troposphere and lower stratosphere (UTLS). The development of Oper-KUMAR tool serves scientific objectives of the Agence National de Recherche (ANR) PyroStrat project (https://anr.fr/Projet-ANR-21-CE01-0028). The Oper-KUMAR tool allows the project participants, as well as a wider atmospheric community, to be informed on the presence of wildfire smoke in the UTLS and endorse the experimental groups with capacity to track the spatial evolution of smoke plumes on a daily basis in order to coordinate related measurement activities.

Scientific and Technical Scope

Intense wildfires release tremendous amounts of heat into the atmosphere, which gives rise to extreme thunderstorms termed Pyrocumulonimbus (PyroCb). These storms, augmented by the energy of combustion, can generate vigorous convective updrafts injecting smoke into the stratosphere, where the residence time of aerosol is not limited by cloud scavenging and precipitation. The presence of wildfire smoke in the atmosphere is readily detectable using satellite observations of carbon monoxide and absorbing aerosols. The latter can be derived from the UV Aerosol Index (AI), a qualitative unitless index indicating the presence of elevated layers of aerosols with significant absorption such as smoke. An advantage of the AI, calculated from wavelength-dependent changes in Rayleigh scattering in the UV spectral range, is that it can be derived for clear as well as (partly) cloudy ground pixels. AI is sensitive to the altitude of the absorbing particles that make up pyroCb plumes (e.g., black and brown carbon), with strongly elevated layers corresponding to the largest values.

Oper-KUMAR uses NRTI data from Sentinel 5 TROPOMI instrument, providing AI measurements with high spatial resolution and daily global coverage, to detect and track the smoke plumes in the UTLS. To distinguish between the tropospheric and stratospheric plumes, OPer-KUMAR analyzes the vertical profiles of aerosol extinction provided by OMPS-LP (limb profiler). In addition, a combination of AI and CO columnar measurements by TROPOMI allows distinguishing smoke plumes from volcanic ash plumes during specific periods, when both wildfire and volcanic aerosols may coexist in the UTLS. Oper-KUMAR was tested and optimized on the basis of available wildfire smoke observations by TROPOMI and OMPS. The threshold values (AI and CO total columns) for detection of PyroCb events for AI and CO have been  established on the basis of the recent wildfire events covered by TROPOMI and OMPS observations as well as using the available literature. An important functionality of Oper-KUMAR is the automatic detection of PyroCb events with a notable impact on the UTLS and alert raising through email notifications, aiming at raising awareness of the experimental teams and planning measurement activities.

Functionalities

1. Automatic download of satellite and meteorological analysis data

Sentinel-5P TROPOMI data

Fully automatic download of Sentinel5 Precursor satellite (https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-5P) near real-time high-resolution imagery of the Absorbing Aerosol Index (AAI) and Carbon Monoxide (CO) columnar amount:

We created Python scripts using Sentinel-Hub API modules from Sentinel Hub https://sentinelsat.readthedocs.io/en/stable/api_overview.html to download and process both Level-2 (L2) offline (OFFL) and Near-Real-Time (NRTI) datasets over the whole globe. The scripts are scheduled to automatically update the L2 NRTI AAI and CO data from TROPOMI instrument (http://www.tropomi.eu/) every hour. These scripts are the part of the operational service described in the following sections.

NCEP GDAS meteorological data

 The wind fields at three pressure levels (100, 150, 200 mbar) are downloaded from from NCEP Global Data Assimilation System (GDAS) database

https://downloads.psl.noaa.gov/Datasets/ncep/

 The winds (U and V components) in the NetCDF format at 2.5 degree spatial resolution are downloaded automatically with the update rate of 1 hour

OMPS-LP aerosol extinction profiles

Suomi-NPP OMPS (Ozone Monitoring and Profiling Suite) L2 AER Daily Product (aerosol extinction profiles) at 1 km vertical resolution are downloaded from:

https://snpp-omps.gesdisc.eosdis.nasa.gov/data/SNPP_OMPS_Level2/OMPS_NPP_LP_L2_AER_DAILY.2/

OMPS-LP V2.0 data on aerosol extinction are checked every 30 minutes  and automatically downloaded

2. Gridding of TROPOMI L2 data

The downloaded TROPOMI L2 CO and AAI data are then regrided to Level-3 (L3) 0.1 degree (~10km for middle latitudes) spatial resolution using shell scripts with HARP software and stored on the server. The software used are:

https://atmospherictoolbox.org/  and  

https://stcorp.github.io/harp/doc/html/harpconvert.html

Everyday along with 4 previous days the maps are updated every hour - the reason for the 4 days window is that TROPOMI OFFL data as well as OMPS-LP profiles come with a delay of several days, and the maps have to be updated accordingly.

We used 0.5 quality assurance value for Carbon Monoxide and 0.75 for the Absorbing Aerosol Index to filter out the pixels with noise and outliers following the ESA TROPOMI ATBD guidance (https://sentinel.esa.int/documents/247904/2476257/sentinel-5p-tropomi-atbd-no2-data-products).

3. Data visualization and mapping

For all the days since June 2018 till now the maps of Absorbing Aerosol Index and Carbon Monoxide with near 10 km spatial resolution were created for both Northern and Southern hemispheres. The visualization is made via web interface with possibility of date selection. The figures are updated operationally every hour once new TROPOMI NRTI L2 data becomes available.

For every day the detection of stratospheric aerosol layers based  on OMPS-LP V2.0 aerosol extinction data is made and corresponding aerosol layer top heights are marked on the map.

The maps are available, for Southern and Northern hemispheres respectively at:

https://thredds-su.ipsl.fr/thredds/fileServer/ipsl_thredds/skhaykin/OperCUMAR_NRTI/SH/TROPOMI_AER_SH_W.html

https://thredds-su.ipsl.fr/thredds/fileServer/ipsl_thredds/skhaykin/OperCUMAR_NRTI/NH/TROPOMI_AER_NH_W.html

The maps are accompanied with the wind fields at 3 different vertical levels, corresponding to three pressure levels: 200, 150 and 100 millibars.

The daily maps are available since July 2018, which enables examining the previous events and their evolution. 

4. Date and  pressure level selection interface

By default, Oper-KUMAR displays the maps for the current date. The previous dates (since July 2018) can be selected using the left and right arrows and a pop-down calendar. Additionally, there is an option to select the pressure level of interest for the wind vectors. Three pressure levels are available: 200, 150, 100 millibar, corresponding to the UTLS at midlatitudes (8-16 km altitude). After selecting a date or a pressure level, the user has to press the button “Show”.