Exploring the Spatiotemporal Variations in Soil Moisture and its Dependence on Climate Drivers in the Maritime Continent

Exploring the spatiotemporal variations in soil moisture in the Maritime Continent

Sreedevi Puthiyamadam Vasu1*, Pallav Ray1, Nathaniel C. Johnson2, Efthymios I. Nikolopoulos3 and Sopia Lestari4

1. Florida Institute of Technology (FIT), 150 W. University Blvd., Melbourne, FL 32904, USA

1. Geophysical Fluid Dynamics Laboratory (GFDL), NOAA, Princeton, NJ 08540-6649, USA

1. Rutgers University-New Brunswick, 500 Bartholomew Road, Piscataway, NJ 08854, USA

1. National Research and Innovation Agency, Jakarta, Indonesia

* spv2023@my.fit.edu

The Maritime Continent (MC) plays an important role in modulating global weather and climate through the release of latent heat of condensation. Among many parameters that control MC convection, soil moisture (SM) is one of them. Yet the spatio-temporal variations of SM in the MC have rarely been studied. We aim to understand the SM variabilities and their local and remote drivers over the MC using Soil Moisture Active-Passive (SMAP) satellite data from 2015 to 2022. The annual SM climatology resembles the annual rainfall pattern, with high SM (above 0.4 mm3/mm3) across the equatorial belt, particularly over the central part of Papua New Guinea. The seasonal evolution of SM follows the monsoonal migration of rainfall, with higher SM during boreal winter (DJF) and lower during April and August. The diurnal cycle of SM contrasts that of precipitation: the precipitation tends to peak in mid-afternoon, soil moisture rises through late afternoon, peaks early the following morning, and then reaches a minimum around noon. The SM also shows significant intraseasonal variability with a 3-day lag with precipitation over the MC. Interestingly, within the intraseasonal timescale, there also exists a 13-day negative correlation between SM and precipitation, suggesting a decrease in SM preceding precipitation over MC. We also explore the role of major climate drivers that influence the SM in the MC using the Empirical Orthogonal Function (EOF) analysis. The first EOF mode is dominated by interannual variability connected with the El-Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). There is a sharp decrease in SM due to decreased precipitation during the combined El-Nino-positive IOD years. The second EOF mode exhibits pronounced intraseasonal variability and is influenced by the Madden-Julian Oscillation (MJO). The results suggest that a decrease in MC soil moisture tends to precede MJO phases 1 and 2 when convection is generally enhanced over the Indian Ocean but suppressed over the eastern MC and western Pacific region by about two weeks. The implications of these results in the SM-precipitation relationship are discussed.