Multi-scale land-atmosphere interactions over South America

Chug, Divyansh

Permalink

https://hdl.handle.net/2142/117791 Copy

Description

Title

Multi-scale land-atmosphere interactions over South America

Author(s)

Chug, Divyansh

Issue Date

2022-12-01

Director of Research (if dissertation) or Advisor (if thesis)

Dominguez, Francina

Doctoral Committee Chair(s)

Dominguez, Francina

Committee Member(s)

• Kumar, Praveen
• Nesbitt, Stephen W
• Taylor, Christopher M

Department of Study

Atmospheric Sciences

Discipline

Atmospheric Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Land-Atmosphere Interactions
• La Plata River Basin
• South America
• Remote Sensing
• Soil Moisture-Precipitation Feedbacks
• Mesoscale Circulations

Abstract

The land surface exerts biogeophysical feedbacks on the atmosphere at time scales ranging from seconds to years. The atmospheric component of this dynamically coupled system evolves differently than what would be expected in the absence of this feedback, due to exchanges of heat, moisture and momentum. These interactions result in numerous pathways through which land modulates the structure of the atmosphere and precipitation from local to global spatial scales. The La Plata river basin (LPB) in South America, one of the most important socio-economic regions in the world, is a "hotspot" of such land-atmosphere (L-A) interactions where land surface feedbacks are important drivers of the regional climate. Past work on L-A feedback processes has established that this region exhibits the necessary "ingredients" for a strong role of the land surface in weather and climate predictability, i.e. large variability in precipitation and surface soil moisture, strong control of soil moisture variability on the variability of surface energy fluxes (latent and sensible), and a heavy dependence on terrestrial sources of moisture for wet season rainfall. Together, these ingredients lead to three important feedback processes (among others) across a range of scales, namely precipitation recycling of terrestrial moisture at the continental scale, thermal feedback of persistent soil moisture anomalies at the regional scale, and mesoscale circulations, a thermal feedback due to soil moisture heterogeneity at the mesoscale. Accurately capturing these feedbacks can improve our ability to predict the weather at a variety of of time-scales ranging from sub-daily to seasonal, and reduce land surface-related biases in climate projections. However, a complete understanding of the role of these feedbacks is lacking due to the following limitations: • The state of our knowledge of the transport and precipitation of terrestrial moisture over South America has primarily been derived from studies that aggregate estimates at seasonal or longer time-scales for individual river basins. The relative importance of the major terrestrial moisture sources at intra-seasonal time-scale is unknown. • The current understanding of the role of land surface variability in atmospheric prediction over South America has largely been derived from numerical modeling experiments. There is little observational validation to support the results and hypothesis derived from modeling studies. • The physical understanding of mesoscale circulations and their role in convection over land has been derived from idealized numerical experiments with idealized representation of soil moisture heterogeneity. The empirical representation of spontaneous patchiness of soil moisture, such as in the real world, is lacking. • There is no past work on quantifying the role of mesoscale circulations forced by soil moisture heterogeneity on convective initiation over subtropical South America. The goal of this dissertation is to advance our current state-of-knowledge about the aforementioned L-A feedback processes over the LPB in South America. Together, these feedback processes represent major biases in climate models and can lead to significant improvements in weather and climate prediction. Through a combined observational and modeling framework, this dissertation addresses the following questions about L-A interactions over South America: 1. What is the role of the land surface as a source of moisture for precipitation over South America at intra-seasonal to seasonal time scales? Using tracers embedded in the Weather Research and Forecasting model, this work quantities the role of the Amazon and the LPB basins as a moisture source to understand the intraseasonal variability in the long-range transport and precipitation of moisture from these sources over the South American continent. Results show an intraseasonal "sloshing" of terrestrial moisture over South America and a relatively larger direct contribution of the LPB source (23%) compared to the Amazon source (5%) for precipitation over southeastern South America during periods of intraseasonal enhancement. 2. Does the antecedent land surface state exert appreciable feedback to the atmosphere at subseasonal time scales over LPB? Using remotely-sensed and reanalysed atmospheric and surface measurements, this work identities the consistently recurring land surface patterns that can potentially induce strong intraseasonal feedbacks at the regional scale and inform future numerical experiments to isolate the physical mechanisms. 3. How does surface heterogeneity, specifically mesoscale gradients in soil moisture, affect convective initiation over subtropical South America? Using satellite data and convection-permitting climate simulations, this work investigates the role of mesoscale circulations induced by soil moisture heterogeneity on atmospheric convection over South America. Results show the first observational evidence for preferential convective initiation on the dry side of mesoscale soil moisture gradients, specifically over "dry patches" on the order of tens of kilometers. The subsequent work quantified and validated the same preference for the first time using long-term (20 years) convection-permitting climate simulations. The research questions addressed in this work are novel for the South American continent. The original contributions of this work include regional moisture budget assessment over South America through improved representation of terrestrial moisture transport, quantification of intra-seasonal variability in terrestrial moisture transport and recycling, identification of organized and persistent soil moisture anomalies associated with the intra-seasonal hydroclimate oscillation, observational evidence for the preference of convective initiation on the dry side of soil moisture gradients on the order of tens of kilometers, and an improved understanding of the length scales of soil moisture heterogeneity associated with convective development. These contributions provide an improved understanding of L-A feedbacks over the most heavily populated and economically active region of South America where accurate weather forecasts and climate prediction are crucial for the prosperity of its 67 million inhabitants.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Divyansh Chug

Owning Collections