Decadal and Seasonal Variability of Aerosol Types and Meteorological Parameters in the Central Himalayas (2014–2024): High-Altitude Analysis from the Third Pole

Vocabulary flashcards covering key concepts, datasets, methods, and findings from the lecture notes on decadal and seasonal aerosol dynamics in the Nepal Central Himalaya (>2500 m, the Third Pole).

Aerosol Optical Depth (AOD)

A measure of the extinction of solar radiation by atmospheric aerosols, representing the total columnar aerosol burden in the atmosphere.

Ångström Exponent (AE)

An indicator of aerosol particle size distribution; higher values imply finer particles, lower values imply coarser particles.

Aerosol Index (AI)

An index highlighting UV-absorbing aerosols (e.g., smoke, dust); high AI indicates the presence of absorbing aerosols.

Third Pole / Nepal Central Himalaya (>2500 m)

A high-elevation region in the central Himalayas used to study aerosol–climate interactions, characterized by rugged terrain and limited ground monitoring.

MODIS Terra Aerosol Monthly Product (MOD08_M3)

Satellite-derived product providing AOD at 550 nm using Deep Blue retrieval for land surfaces.

Ångström Exponent wavelength range (470–660 nm)

Wavelength channels used to derive AE from MODIS data to infer particle size distribution.

UV Aerosol Index (AI) from TROPOMI

Satellite-derived index detecting UV-absorbing aerosols; used from 2019 onward to identify absorbing particles like dust and smoke.

CHIRPS

Climate Hazards Group InfraRed Precipitation with Stations; high-resolution precipitation dataset combining satellite and station data.

FLDAS

Global Land Data Assimilation System providing meteorological variables (e.g., Tmax, relative humidity, wind speed) for study area.

Mann–Kendall trend test

Non-parametric method to detect monotonic trends in time series without assuming normality.

Sen’s Slope estimator

Non-parametric method to quantify trend magnitude as the median slope between time-ordered observations.

Spatial mask above 2500 m

A geographic filter using SRTM data to include only pixels located above 2500 meters in Nepal.

Seasonal definitions (DJF, MAM, JJA, SON)

Winter (DJF), Spring (MAM), Summer (JJA), Autumn (SON); winter includes December of the preceding year.

Aerosol-type classification using AE and AI thresholds

Categorization into fine-mode urban/anthropogenic, coarse-mode dust, or clean/background based on AE and AI values.

Seasonal amplitude of aerosol parameters

Yearly calculation of the seasonal fluctuation in variables like AOD and AE to identify anomalies.

Transboundary aerosol transport from the Indo-Gangetic Plain (IGP)

Long-range movement of aerosols from southern Asia northward into the Himalayas, aided by regional winds.

Interannual variability vs long-term trend

Year-to-year fluctuations in aerosol properties that may occur without a statistically significant decadal trend.

Correlation findings between aerosols and meteorology

AOD positively correlates with maximum temperature and precipitation; AE negatively correlates with maximum temperature; both Pearson and Spearman tests used.

Lack of statistically significant long-term trends (p > 0.05)

Despite small positive Sen’s slopes for AOD and AE, no trend reached conventional significance over 2014–2024.

Aerosol–climate coupling in high-altitude Himalaya

Interplay between aerosols and meteorological variables showing non-linear, seasonally modulated relationships.

Monsoonal cleansing

Seasonal rainfall reduces aerosol loads, contributing to lower background pollution during monsoon seasons.

Data sources and processing tools

MODIS (AOD/AE), TROPOMI AI, CHIRPS (precipitation), FLDAS (Tmax, RH, wind); processed in Google Earth Engine with a 2500 m elevation mask.