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Emilee Lachenmeier
,
Rezaul Mahmood
,
Chris Phillips
,
Udaysankar Nair
,
Eric Rappin
,
Roger A. Pielke Sr.
,
William Brown
,
Steve Oncley
,
Joshua Wurman
,
Karen Kosiba
,
Aaron Kaulfus
,
Joseph Santanello Jr.
,
Edward Kim
,
Patricia Lawston-Parker
,
Michael Hayes
, and
Trenton E. Franz

Abstract

Modification of grasslands into irrigated and nonirrigated agriculture in the Great Plains resulted in significant impacts on weather and climate. However, there has been lack of observational data–based studies solely focused on impacts of irrigation on the PBL and convective conditions. The Great Plains Irrigation Experiment (GRAINEX), conducted during the 2018 growing season, collected data over irrigated and nonirrigated land uses over Nebraska to understand these impacts. Specifically, the objective was to determine whether the impacts of irrigation are sustained throughout the growing season. The data analyzed include latent and sensible heat flux, air temperature, dewpoint temperature, equivalent temperature (moist enthalpy), PBL height, lifting condensation level (LCL), level of free convection (LFC), and PBL mixing ratio. Results show increased partitioning of energy into latent heat relative to sensible heat over irrigated areas while average maximum air temperature was decreased and dewpoint temperature was increased from the early to peak growing season. Radiosonde data suggest reduced planetary boundary layer (PBL) heights at all launch sites from the early to peak growing season. However, reduction of PBL height was much greater over irrigated areas than over nonirrigated croplands. Relative to the early growing period, LCL and LFC heights were also lower during the peak growing period over irrigated areas. Results note, for the first time, that the impacts of irrigation on PBL evolution and convective environment can be sustained throughout the growing season and regardless of background atmospheric conditions. These are important findings and applicable to other irrigated areas in the world.

Significance Statement

To meet the ever-increasing demand for food, many regions of the world have adopted widespread irrigation. The High Plains Aquifer (HPA) region, located within the Great Plains of the United States, is one of the most extensively irrigated regions. In this study, for the first time, we have conducted a detailed irrigation-focused land surface and atmospheric data collection campaign to determine irrigation impacts on the atmosphere. This research demonstrates that irrigation significantly alters lower atmospheric characteristics and creates favorable cloud and convection development conditions during the growing season. The results clearly show first-order impacts of irrigation on regional weather and climate and hence warrant further attention so that we can minimize negative impacts and achieve sustainable irrigation.

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Hiroyuki Kusaka
,
Satoshi Nishiba
, and
Yuki Asano

Abstract

The Jintsu-oroshi refers to Japan’s south foehn, which blows over the Toyama Plain in the Hokuriku region. This region faces the Sea of Japan to the north and the central mountain range to the south. The Jintsu-oroshi occurs more frequently at night than during the day. In this study, we determined the primary factors causing this feature using the Weather Research and Forecasting (WRF) Model. We selected a typical Jintsu-oroshi case in May 2016 for analysis. An extratropical cyclone traversed the Sea of Japan during the event, leading to a temporal change in the synoptic-scale pressure pattern. The observations and numerical simulation results showed that the collapse of the mixed layer over the mountains and the end of the sea breeze are key factors for the nighttime onset of the Jintsu-oroshi. Indeed, mountain waves and their resulting downslope winds did not occur under near-neutral atmospheric stability conditions over the mountains during the daytime. After sunset, the atmospheric stability changed to stable conditions, which caused the downslope winds to blow. However, the downslope winds did not reach the plains because of the sea breeze. After several hours, the sea breeze disappeared, and the downslope winds reached the leeward plains and increased the temperature there. Similar features were confirmed in August 2013 for another typical Jintsu-oroshi case under atmospheric conditions, without temporal changes in the synoptic-scale pressure pattern. We expect the results obtained in this study to advance our understanding of foehn occurrence in regions where mountains adjoin seas, similar to the coastal areas adjacent to the Sea of Japan.

Significance Statement

The Jintsu-oroshi refers to Japan’s south foehn, which blows over the Toyama Plain in the Hokuriku region. This foehn occurs more frequently at night than during the day. Strong foehns enhance the risk of fire. Nocturnal high temperatures due to foehns can cause sleeplessness in people. Nighttime foehns cause damage to paddy rice. Analyses of observations and numerical simulations for the two typical cases showed that Jintsu-oroshi did not tend to occur during the daytime because the development of a convective boundary layer over the mountains and sea breezes in the leeward plain inhibited the occurrence of the downslope winds. We expect the results obtained in this study to advance our understanding of foehn occurrence in regions where mountains adjoin seas, similar to the coastal areas adjacent to the Sea of Japan.

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Joana Mendes
,
Nosipho Zwane
,
Brighton Mabasa
,
Henerica Tazvinga
,
Karen Walter
,
Cyril J. Morcrette
, and
Joel Botai

Abstract

We assess site-specific surface shortwave radiation forecasts from two high-resolution configurations of the South African Weather Service numerical weather prediction model, at 4 and 1.5 km. The models exhibit good skill overall in forecasting surface shortwave radiation, with zero median error for all radiation components. This information is relevant to support a growing renewable energy sector in South Africa, particularly for photovoltaics. Further model performance analysis has shown an imbalance between cloud and solar radiation forecasting errors. In addition, cloud overprediction does not necessarily equate to underestimating solar radiation. Overcast cloud regimes are predicted too often with an associated positive mean radiation bias, whereas the relative abundance of partly cloudy regimes is underpredicted by the models with mixed radiation biases. Challenges highlighted by the misrepresentation of partly cloudy regimes in solar radiation error attribution may be used to inform improvements to the numerical core, namely, the cloud and radiation schemes.

Significance Statement

This paper provides the first comprehensive assessment of high-resolution site-specific NWP forecasts of surface shortwave radiation in South Africa, exploring clouds as the main drivers of prediction biases. Error attribution analyses of this kind are close to none for this part of the world. Our study contributes to understanding how cloud and radiation schemes perform over South Africa, representing a step forward in the state of the art. In addition to the scientific interest, the capabilities developed through this work may benefit the second largest economy of the continent. In a country where energy security is of critical relevance, the availability of useful and usable weather information is paramount to support its industry and socioeconomic growth.

Open access
Jodie Clark
and
Sen Chiao

Abstract

This study investigates the connection between the arrival of dry stratospheric air and the Soberanes Fire (2016). The Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) and Goddard Earth Observing System Forward Processing model (GEOS-FP) are used for back-trajectories and offshore deep stratospheric intrusion in conjunction with the ignition and outbreak of the fire. The back-trajectory analysis indicates that most air reaching the vertical column was critically dry, exhibiting relative humidity values below 10%. As the fire ignited, dry air arrived from due west at heights of 1–3 km about 24 h prior. During the overnight fire growth, dry air arrived from the northwest to north-northwest at heights of 3.5–5.5 km 48–72 h prior. The synoptic and GEOS-FP analyses demonstrate offshore mid-to-low stratospheric intrusion. On 21 July 2016, an enclosed upper-level low approached the California–Oregon border along the northwesterly subtropical jet stream hours before the fire outbreak. The GEOS-FP results of potential vorticity, specific humidity, and ozone along the back-trajectories to the west and northwest of the fire suggest a stratospheric intrusion event into the mid-to-low troposphere at the back-trajectory start points, and vertical velocity indicates sinking motion. The specific humidity analyzed at the arrival time shows the transport of the abnormally dry air to the Soberanes Fire. Results suggest a connection between dry stratospheric air transported to the Soberanes Fire at ignition and overnight accelerated growth, supported by a dark bank in satellite water vapor imagery. The prediction of low-level transport of dry stratospheric air to the coastal communities could help to predict the occurrence of wildfire outbreaks, or periods of accelerated fire growth.

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Andra J. Garner
and
Daniel P. Duran

Abstract

Large temperature variations in a temperate climate, particularly in late winter and early spring, can be disruptive for native ecosystems and agricultural crops. As warmer temperatures occur earlier in the year in midlatitude regions as a result of anthropogenic climate change, springtime temperatures may become less consistent, leading to potential damage to species and crops that are vulnerable to the return of historically cooler temperatures, including late-spring frosts, after an initial warm-up. In this work, we quantify shifting patterns in late-winter and springtime temperature variations at eight sites across New Jersey from 1950 to 2019. Many sites located along the coast or in the coastal plain experience increases in the number of times the temperature climbs above 15.5°C (60°F) and then falls below freezing (i.e.,0°C, or 32°F). Sites in southern New Jersey (where much of the state’s agriculture is located) experience the most significant (P < 0.05) increases in large springtime temperature variations. Across all sites, there is a general increase in both the percentage and magnitude of temperature variations that occur as early as February. At 75% of sites, day-to-day variation in daily maximum temperature has increased from the 1950s through 2019; day-to-day variation in daily minimum temperatures has increased over the same time at more than half of sites considered. These amplifications in extreme temperature variations indicate the need for both mitigation and adaptation strategies to protect vulnerable crops and ecosystems in the region during this critical time of the year.

Significance Statement

Human-caused climate change has made it more likely for warmer temperatures to occur earlier in the year, causing many locations to experience late-winter and early-springtime temperatures that are less consistent than they may have been in the past. These variations can be highly problematic for both vital agricultural crops and critical ecosystems. Here, we evaluate how late-winter and early-springtime temperatures have changed throughout New Jersey (home to a variety of agriculture and unique ecosystems) from the mid-twentieth century until 2019. We find critical changes to temperature patterns during late winter and early spring, including larger and more frequent temperature swings (particularly in February) and increased day-to-day variation in high and low temperatures.

Open access
Samuel A. Marlow
,
John M. Frank
,
Matthew Burkhart
,
Bujidmaa Borkhuu
,
Shelby E. Fuller
, and
Jefferson R. Snider

Abstract

Snowfall is an important driver of physical and biological processes in alpine systems. Previous work has shown that surface deposition of snow can vary for reasons not directly related to precipitation processes and that this variance has consequence for water budgets in snow-dominated terrestrial systems. In this work, measurements were made over several winter seasons in a forest–meadow ecotone in the Rocky Mountains of southeastern Wyoming. Two groups of measurements—both with wind-exposed and sheltered precipitation gauges—were analyzed. Reasonable agreement between snow deposition from a Hotplate gauge (exposed) and snow deposition from a SNOTEL pillow gauge (sheltered) is reported. The other result is that snow deposition is enhanced at an exposed gauge that was deployed on the leeward side of a forest–meadow edge. The enhancement is approximately a factor of 2 and varies with wind direction and speed and with upwind forest coverage. The enhancement is greater than was documented in an earlier investigation of Rocky Mountain snow deposition; however, in that study measurements were conducted above tree line.

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Longtao Wu
,
Hui Su
,
Xubin Zeng
,
Derek J. Posselt
,
Sun Wong
,
Shuyi Chen
, and
Ad Stoffelen

Abstract

Atmospheric winds are crucial to the transport of heat, moisture, momentum, and chemical species, facilitating Earth’s climate system interactions. Existing weather and climate studies rely heavily on the wind fields from reanalysis datasets. In this study, we analyze the uncertainty of instantaneous atmospheric winds in three reanalysis (ERA5, MERRA-2, and CFSv2) datasets. We show that the mean wind vector differences (WVDs) between the reanalysis datasets are about 3–6 m s−1 in the troposphere. The mean absolute wind direction differences can be more than 50°. Large WVDs greater than 5 m s−1 are found for 30%–50% of the time when the observed precipitation rate is larger than 0.1 mm h−1 over the eastern Pacific Ocean, Indian Ocean, Atlantic Ocean, and some mountain areas. The mean WVDs exhibit seasonal variations but no significant diurnal variations. The uncertainty of vertical wind shear has a correlation of 0.59 with the uncertainty of winds at 300 hPa. The magnitudes of vorticity and horizontal divergence uncertainties are on the order of 1 × 10−5 s−1, which is comparable to the mean values of vorticity and horizontal divergence. In comparison with some limited observations from field campaigns, the reanalysis datasets exhibit a mean WVD ranging from 2 to 4.5 m s−1. Among the three reanalysis datasets, ERA5 shows the closest agreement with the observations while MERRA-2 has the largest discrepancy. The substantial uncertainty and errors of the reanalysis wind products highlight the critical need for new satellite missions dedicated to 3D wind measurements.

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Reinel Sospedra-Alfonso
,
William J. Merryfield
,
Viatsheslav V. Kharin
,
Woo-Sung Lee
,
Hai Lin
,
Gulilat T. Diro
, and
Ryan Muncaster

Abstract

We evaluate the soil moisture hindcasts and the reconstruction runs giving the hindcasts initial conditions in version 2.1 of the Canadian Seasonal to Interannual Prediction System (CanSIPSv2.1). Different strategies are used to initialize the hindcasts for the two CanSIPSv2.1 models, CanCM4i and the coupled Global Environmental Multiscale, version 5.1, (GEM5)–NEMO model (GEM5-NEMO), with contrasting impacts on the soil moisture initial conditions and forecast performance. Forecast correlation skill is decomposed into contributions from persistence of the initial anomalies and contributions not linked to persistence, with performance largely driven by the accuracy of the initial conditions in regions of strong persistence. Seasonal soil moisture correlation skill is significant for several months into the hindcasts depending on initial and target months, with contributions not linked to persistence becoming more notable at longer lead times. For the first 2–4 months, the quality of CanSIPSv2.1 ensemble mean forecasts tends to be higher on average during summer and fall and is comparable to that of the best performing model, whereas CanSIPSv2.1 outperforms the single models during spring and winter. For longer lead times, remote climate influences from the Pacific Ocean are notable and contribute to predictable soil moisture variability in teleconnected regions.

Open access
Austin P. Hope
,
Israel Lopez-Coto
,
Kris Hajny
,
Jay M. Tomlin
,
Robert Kaeser
,
Brian Stirm
,
Anna Karion
, and
Paul B. Shepson

Abstract

We investigated the ability of three planetary boundary layer (PBL) schemes in the Weather Research and Forecasting (WRF) Model to simulate boundary layer turbulence in the “gray zone” (i.e., resolutions from 100 m to 1 km). The three schemes chosen are the well-established MYNN PBL scheme and the two newest PBL schemes added to WRF: the three-dimensional scale-adaptive turbulent kinetic energy scheme (SMS-3DTKE) and the E–ε parameterization scheme (EEPS). The SMS-3DTKE scheme is designed to be scale aware and avoid the double counting of TKE in simulations within the gray zone. We evaluated their performance using aircraft measurements obtained during three research flights immediately downwind of Manhattan, New York City, New York. The MYNN PBL scheme simulates TKE best, despite not being scale aware and slightly underestimating TKE from observations, whereas the SMS-3DTKE scheme appears to be overly scale aware for the three flights examined, in particular, when combined with the MM5 surface layer scheme. The EEPS scheme significantly underestimates TKE, mostly in the elevated layers of the boundary layer. In addition, we examined the impact of flow over tall buildings on observed TKE and found that only the windiest day showed a significant increase in TKE directly downwind of Manhattan. This impact was not reproduced by any of the model configurations, regardless of the land-use data selected, although the better resolved National Land Cover Database (NLCD) land use led to a slight improvement of the spatial distribution of TKE, implying that more explicit representation of the impact of tall buildings may be needed to fully capture their impact on boundary layer turbulence.

Significance Statement

Because the majority of the world’s population lives in cities, it is important to accurately simulate the atmosphere above and around these cities including the turbulence caused by tall buildings. This turbulence can significantly impact the mixing and dilution of air pollutants and other toxins in highly populated urban environments. The scale of cities often falls into what is known as the “gray zone” for turbulence modeling, which has been analyzed theoretically before but rarely in varied real-world conditions. Our analysis around New York City, New York, suggests that model turbulence schemes can match observations relatively well even at gray zone scales, although newer schemes require refinement, and all schemes tend to underestimate turbulence downwind of tall buildings.

Open access
Chunyan Zhang
,
Donghai Wang
,
Lebao Yao
,
Zhenzhen Wu
,
Qianhui Ma
,
Yongsheng Li
, and
Peidong Wang

Abstract

This study investigates and compares large-scale moisture and heat budgets over the eastern rainy sea area around Dongsha, the western rainless sea area around Xisha, and the northern coastland of the South China Sea. Ten-year (2011–20) surface, balloon-sounding, satellite measurements, and ERA5 reanalysis are merged into the physically consistent data to study annual and vertical variations of the budgets. It shows that the surface and column-integrated heat and moisture budgets have the smallest annual evolution over the coastland. The latent heat as a key heat contributor in summer is mainly offset by total cold advection and partially offset by net radiative cooling. The horizontal moisture advection below 700 hPa presents moistening over the sea whereas drying over the coastland during rainy months, in which the vertical moisture advection presents moistening up to 250 hPa for all three subregions. The horizontal temperature advection is weak throughout the year over the sea but displays strong top warming and bottom cooling in summer and nearly the opposite in winter over the coastland. The diabatic cooling with a peak at ∼700 hPa in winter is largely due to the enhanced radiative cooling and latent cooling. While the diabatic heating with a peak at ∼500 hPa in summer is largely due to the enhanced latent heating. The earliest atmospheric heating and moistening occur in spring over the coastland, inducing the earliest precipitation increase. The enhanced heating and moistening over Xisha have a 1-month lag relative to Dongsha, resulting in lagging precipitation.

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