Precipitation Interactions with the Earth's Surface

Abstract

Precipitation is a critical component of the Earth’s water cycle and energy budget. It can shape the environment via erosion and flooding as well as support life on Earth via access to fresh water for agriculture and drinking. However, precipitation is one of the most difficult atmospheric parameters to quantify and its relationships with the Earth’s surface require further study. The challenges in understanding precipitation’s relationship with the Earth’s surface vary depending on the region and environment where the precipitation is taking place. In polar environments, precipitation is sensitive to sea ice conditions and vice versa, while in continental environments, precipitation is sensitive to soil moisture and vice versa. In both polar and marine environments in situ observations of precipitation are limited due to the remote nature of the regions. In all environments, there are difficulties in measuring solid precipitation at the surface, as winds can more easily blow snow away from gauges and the liquid water content of snow varies depending on atmospheric conditions. Since precipitation can occur at such small temporal and spatial scales in all environments and over remote regions, it can be difficult to capture globally complete precipitation rates from in situ measurement or to parameterize them in climate models. This dissertation takes a holistic approach to addressing these challenges by investigating the impacts of precipitation in marine, polar, and continental environments. The first study (Marcovecchio et al. 2023), analyzed the relationship between precipitation and marine boundary layer clouds using measurements and retrievals from field campaigns the East North Atlantic and Southern Ocean. Both regions are in marine environments with relatively high frequency occurrences of low-level, liquid dominant MBL clouds, but are in different hemispheres with different weather patterns. A summary of the study is as follows: we compared the cloud and drizzle macrophysical and microphysical properties of single-layer, liquid dominant marine boundary layer clouds and associated drizzle from the two field campaigns. Using field campaign data allows us to address the lack of in situ precipitation measurements at a consistent temporal and spatial resolution in marine regions. The results have shown that the Southern Ocean campaign has a higher drizzle frequency rate and a lower specific humidity that leads to a higher drizzle base than that of ENA. By improving our process level understanding of drizzle in each location, we may help to address the difficulties in parameterizing precipitation at small temporal and spatial scales in models. This work was published in the Journal of Geophysical Research – Atmospheres. While the first study (Marcovecchio et al., 2023) investigates process level understanding of precipitation within the marine boundary layer atmosphere, the second study (Marcovecchio et al., 2021) investigates the relationship between precipitation and sea ice melt onset in a polar environment in the East Siberian Sea and the Laptev Sea. Sea ice season melt onset timing can vary interannually by up to three weeks, but models are still unable to pinpoint the timing of melt onset accurately. In the study, the results have shown when changes in precipitation phase and intensity may be significantly different before and after the melt onset of sea ice. One important conclusion of this study was that precipitation contributes to the initiation of ice melt and precipitation might also initiate albedo feedback processes. Specifically, we compare four years with early melt onset to four years with late melt onset in the area of focus to better compare the different responses to melt onset timing. The area of focus was selected because the atmosphere is most sensitive to sea ice melt onset in this region. There is not yet a high-quality ground-truth Arctic precipitation data product, so a consistency check is performed between MERRA-2, ERA-Interim, and ERA5 reanalysis Arctic precipitation products and the GPM GPCP satellite- and ground-based observational product. We found that all three reanalyses would yield the same conclusions, but spotlight one reanalysis in the article based on how it represents seasonal trends. For early melt years, we found that surface sensible flux loss and precipitation are above average in the days before and after the first major melt event, which represents heat and moisture transport coming into the area of focus from the midlatitudes. However, surface sensible heat flux loss and precipitation are below average in the month leading up to the first major melt event during late melt years. Instead, melt onset in late melt years is associated with the atmosphere reaching average seasonal conditions, as they had been below average in the weeks leading up to the first major melt event. This work is published in the International Journal of Climatology. Since the first and second study focus on marine precipitation, in the third study we investigate the relationship between precipitation and the land surface. As mentioned previously, in continental environments, precipitation is sensitive to soil moisture and vice versa. Accurate soil moisture information is important because it can be used to predict flood events, soil strength, and streamflow. The third study uses the Noah-MP land surface model to investigate how uncertainties in precipitation and other meteorological forcings propagate through Noah-MP and impact soil moisture. This study analyzes soil moisture and surface turbulent fluxes (sensible heat and latent heat) Noah-MP outputs as well as precipitation and temperature from ERA5 (ECMWF Reanalysis Version 5), GDAS (Global Data Assimilation System), and US Air Force Weather Analysis (AFWA) meteorological forcing datasets. Soil moisture from Noah-MP is compared to in-situ measurements from the USCRN (U.S. Climate Reference Network) and Level 3 satellite observations from SMAP (Soil Moisture Active Passive). Model output of sensible heat (SH) and latent heat (LH) are compared to in-situ flux tower measurements at ARM Southern Great Plains. We found that ERA5 has the best statistical comparisons for precipitation, with a bias lower two orders of magnitude smaller than the other forcing datasets. This contributes to ERA5 having a statistically the best soil moisture with a slightly better correlation, RMSE, and ubRMSE than AFWA relative to in situ data. In investigating how precipitation forcing uncertainties propagate through the Noah-MP model, we help to address one of the difficulties in parameterizing precipitation in models. Overall, this dissertation takes a broad approach to improving our understanding of precipitation interaction with the Earth’s surface in three different environments: marine, polar, and continental. The first study (Marcovecchio et al., 2023) improves our understanding of microscale process-level knowledge of drizzle formation, which can help improve precipitation parameterizations in marine regions, and also uses field campaigns to address the sparsity of in situ measurements. The second study (Marcovecchio et al., 2021) compares precipitation data sources to address limited in situ observations in the polar environment and addresses relationships between sea ice and precipitation. Finally, the third study investigates the impacts of precipitation and meteorological forcings on soil moisture in a continental environment. It addresses the high variability of precipitation by seeing how its uncertainty propagates through land surface models and discusses how precipitation can impact soil moisture conditions at the land surface. The diverse focus areas of each study enable the exploration of precipitation over land, ocean surfaces (including sea ice), and within the marine boundary layer, enhancing our understanding of how precipitation interacts with the Earth's surface.