R. Paul Acosta
Understanding Mountain Climate and Monsoon Systems
Contact Information
Postdoctoral Research Fellow
email: acostar@umich.edu
Earth and Environmental Science Department
University of Michigan, Ann Arbor, MI 48109
About Me
A passionate climate scientist who works on deep-time, historical, and future climate change. Expertise in using state-of-the-art numerical climate models and data processing workflows for geospatial data. Proficient programming skills in R, NCAR NCL, Matlab, and Python. Enthusiastic to collaborate with a diverse, and mission-driven workforce to tackle pressing climate and environmental problems.
I am an Earth science buff and pretty much an enthusiast for any type of science. In particular, I have a deep interest in the interactions between mountains and the atmosphere. I received my undergraduate geology degree from the University of California Santa Cruz. There I got interested in the cloud forest or fog-driven ecosystems, which piqued my curiosity toward ocean-air-mountain interaction. Such curiosity eventually drove me to stop looking at rocks on the ground, and begin to look up at the sky. So decided to go to Purdue University and pursue a Master's and Doctoral degree in atmospheric and climate sciences. In between my masters and my current PhD., I briefly attended the University of New Hampshire to study small-scale, regional dynamics in terrestrial and aquatic systems. There, I worked on future climate change projections across the greater New England, US, using dynamically downscaling climate model output into weather prediction models such as WRF. For my Ph.D., I focused on the interaction between the Indo-Asian Monsoon system and the orogeny of the Tibetan Plateau, using the high-resolution NCAR global climate model CESM. Today, I am Postdoc at the University of Michigan researching the paleoclimatic evolution of South America, and Africa by using CESM to simulate paleoclimate periods such as the Miocene, Eocene, and Cretaceous.
My true passion lies in the heart of the mountains. You can always guess that I am either hiking somewhere, climbing some rocks, out camping/backpacking (I’m sure that constitutes as hiking), and once in a while I’m biking or frolicking by the ocean (if and when available). With that said, I am genuinely interested in understanding the fate of Earth's high mountain range, especially under unprecedented anthropogenic-driven climate change. My goal is to use modern state-of-the-art tools and combine them with past historical or paleo records to help us understand how climate change will impact our mountains.
Research
Indo-Asian Monsoon
The Indo-Asian monsoon is one of the most studied hydrological systems (Fig. 1). Rightfully so, due to its immense influence on billions of lives. Simple delay of the monsoon onset causes havoc on Asia's agriculture and changes in its magnitude create devastating floods or droughts. In colloquial terms, monsoon regions are defined as areas where the majority of its rainfall occurs during one particular season. In the case of India, most of the rainfall occurs during June, July, and August with seasonal growth and decay occurring during May and September. The figures below are typical data outputted from climate models where the colors represent a given variable such as temperature or humidity while vectors typically show the transport of wind. In the case of figure 1, the color bar is showing surface elevation where the highest surface elevation is in brown and gray.
The Indo-Asian Monsoon has a unique relationship with the surrounding terrain. As shown in figure 1, Asia contains the Himalayan-Tibetan complex, as well as smaller but nonetheless important mountain ranges such as the Western Ghats, Mizoram Mountains, and the Iranian Plateau. Together these collections of mountains act as obstacles that redirect or block the summer onshore monsoon air. We can see in figure 2 the vectors which represent the onshore monsoon flow enters from the Arabian sea from the left, encounters the Western Ghats moves across Southern India then heads north from the Bay of Bengal into Bangladesh into the Indo-Gangetic Plains. One should notice the shorelines with elevated terrain experience the most summer rainfall. Moving away from the coast enhanced rain occurs along the Himilayas as well as the Ganges Basin. Increased rainfall over the Himalayas, Western Ghats, and Mizoram Mountains occur due to a process known as orographic lifting, where moist air is rapidly cooled as they are forced up the mountain. The rainfall over the Ganges basin is a stationary atmospheric phenomenon known as a low-pressure system. Notice the cyclonic circulation which recycles moisture in-and-out of the Bay of Bengal.
During my Ph.D. I spent an immense amount of time trying to understand what affects the Ganges Basin low-pressure system. One avenue of research that transpired out of it was how the surrounding mountain ranges modulate this feature which ultimately led to the low-level wind found across the Indo-Gangetic Plain. The next section explores the mechanics behind the Indo-Gangetic Low-Level Jet.
Figure 1. In colors are simulated July and August rainfall rate (mm/day) over Indo-Asia. Vectors are near surface moisture and wind transported. The climatology used spans over 2001-2010. Output from High-Asia reanalysis product.
Figure 2. Visualization of the South Asian topography used by various climate models. Color bar representing height in meters.
Indo-Gangetic Low-Level Jet
It is well understood that at the regional level, surface-atmosphere interactions, including topography, are important for the local IAM characteristics. Thus, characterizing the correct expression of the Indo-Asian Monsoon is limited by the ability of atmospheric general circulation models to capture regional-scale circulation. This has proven to be challenging, but the availability of higher resolution modeling has substantially improved the representation of the IAM in climate model simulations. Significant challenges remain, especially simulating rainfall over Himalayan mountains where model-data disagreement increases toward higher elevation. Accurately simulating the onshore flow of moisture into the Indo-Gangetic Plain, Ganges Basin and the Himalayan Mountains is crucial for understanding the Indo-Asian Monsoon. Since the monsoon field has placed little emphasis on elucidating the phenomenology and dynamics of the northern branch of the Indo-Asian Monsoon, we demonstrated the existence of an easterly low-level jet over the Indo-Gangetic Plain during peak monsoon season.
Figure 3. In colors are simulated vertical profile of zonal winds (m/s) over Indo-Asia (70E-90E). The climatology used is the averaged of July and August spaning over 2001-2010. Output from High-Asia reanalysis product
Paleoaltimetry
Stable isotopes of water generated from terrestrial proxy records, are seminal tools used to estimate the ancient elevation of the Andes. However, understanding climatic and tectonic impacts on water isotope records is dependent on complex climate-atmosphere-land-ocean interactions, which in turn have confounded consensus on how the Andes grew through the Cenozoic. As a postdoc, I use state-of-the-art global climate models to elucidate the surface history of the Andean and Tibetan Plateau and understand how they impact the local and global atmosphere. As shown in figure 4, mountains like the Andes found in South America reveal a district isotopic gradient which can be used to estimate the height of the mountains. By combining proxy records and paleoclimate modelling we can better approximate past large-scale orogenic events such as the uplift of the Andes or the Tibetan Plateau.
Paleoclimate
In progess...
