Abstract
The presence of an aerosol layer in the upper troposphere/lower stratosphere (UT/LS) in South America was identified with the Modern-Era Retrospective analysis for Research and Application Aerosol Reanalysis Version 2 (MERRA-2). This layer, which we shall refer to as the South American Tropopause Aerosol Layer (SATAL) was identified over the Amazon Basin at altitudes between 11-14 km. It exhibits a seasonal behavior similar to the Asian Tropopause Aerosol Layer (ATAL) and the North American Tropopause Aerosol Layer (NATAL). The SATAL is observed from October to March, coinciding with the presence of the South American monsoon. It forms first in the eastern Amazon Basin in October, then moves to the Southern Amazon, where it weakens in December-January and finally dissipates in February-March. We hypothesize that two main factors influence the SATAL formation in the UT/LS: 1) the source of aerosols from Africa; 2) the updraft mass flux from deep convective systems during the active phase of the South American Monsoon System that transports aerosols to the UT/LS. Further satellite observations of aerosols and field campaigns are needed to provide useful information to find the origin and composition of the aerosols in the UT/LS during the South American Monsoon.
Abstract
The presence of an aerosol layer in the upper troposphere/lower stratosphere (UT/LS) in South America was identified with the Modern-Era Retrospective analysis for Research and Application Aerosol Reanalysis Version 2 (MERRA-2). This layer, which we shall refer to as the South American Tropopause Aerosol Layer (SATAL) was identified over the Amazon Basin at altitudes between 11-14 km. It exhibits a seasonal behavior similar to the Asian Tropopause Aerosol Layer (ATAL) and the North American Tropopause Aerosol Layer (NATAL). The SATAL is observed from October to March, coinciding with the presence of the South American monsoon. It forms first in the eastern Amazon Basin in October, then moves to the Southern Amazon, where it weakens in December-January and finally dissipates in February-March. We hypothesize that two main factors influence the SATAL formation in the UT/LS: 1) the source of aerosols from Africa; 2) the updraft mass flux from deep convective systems during the active phase of the South American Monsoon System that transports aerosols to the UT/LS. Further satellite observations of aerosols and field campaigns are needed to provide useful information to find the origin and composition of the aerosols in the UT/LS during the South American Monsoon.
Abstract
Water scarcity threatens agriculture in California. During the last two decades, historically severe droughts have led to severe water shortages. Under projected changes in climate, droughts of greater severity and duration will exacerbate this situation. California produces 80% of the world’s almonds, which require consistent water supplies for irrigation. Almonds are the most commonly grown crop in California, covering nearly 1.4 million acres over about 8,000 farms. In response to these challenges, almond growers are considering a myriad of management strategies to save water and mitigate climate change. The Tree-crop Remote sensing of Evapotranspiration eXperiment (T-REX) aims to identify water and orchard management opportunities to maximize water use efficiency and carbon sequestration in almonds and other woody perennial tree crops. The project combines satellite, uncrewed aerial vehicles, and proximal sensing technologies to retrieve key variables used to model surface fluxes and biophysical properties. We aim to advance our understanding of water management and cultural practices on water-carbon relationships in tree-perennial agroecosystems. Through new methods, such as Evapotranspiration-based irrigation scheduling, even a modest 10% decrease in almond orchard irrigation across the state equates to about a third of the water in Lake Oroville, California’s second-largest reservoir, at average levels. From a carbon perspective, almond orchards could sequester 8% of the state’s current greenhouse gas emissions by transitioning toward climate-smart practices. As such, the almond industry is uniquely positioned to curb water-use and contribute to climate change mitigation while maintaining economic viability of almond production. An overview of initial results related to evapotranspiration observational and modeling uncertainty, and carbon sequestration potential are presented in this article.
Abstract
Water scarcity threatens agriculture in California. During the last two decades, historically severe droughts have led to severe water shortages. Under projected changes in climate, droughts of greater severity and duration will exacerbate this situation. California produces 80% of the world’s almonds, which require consistent water supplies for irrigation. Almonds are the most commonly grown crop in California, covering nearly 1.4 million acres over about 8,000 farms. In response to these challenges, almond growers are considering a myriad of management strategies to save water and mitigate climate change. The Tree-crop Remote sensing of Evapotranspiration eXperiment (T-REX) aims to identify water and orchard management opportunities to maximize water use efficiency and carbon sequestration in almonds and other woody perennial tree crops. The project combines satellite, uncrewed aerial vehicles, and proximal sensing technologies to retrieve key variables used to model surface fluxes and biophysical properties. We aim to advance our understanding of water management and cultural practices on water-carbon relationships in tree-perennial agroecosystems. Through new methods, such as Evapotranspiration-based irrigation scheduling, even a modest 10% decrease in almond orchard irrigation across the state equates to about a third of the water in Lake Oroville, California’s second-largest reservoir, at average levels. From a carbon perspective, almond orchards could sequester 8% of the state’s current greenhouse gas emissions by transitioning toward climate-smart practices. As such, the almond industry is uniquely positioned to curb water-use and contribute to climate change mitigation while maintaining economic viability of almond production. An overview of initial results related to evapotranspiration observational and modeling uncertainty, and carbon sequestration potential are presented in this article.
Abstract
We assess site-specific surface short-wave radiation forecasts from two high resolution configurations of the South African Weather Service numerical weather prediction model, at 4 km and 1.5 km. The models exhibit good skill overall in forecasting surface short-wave 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 over-prediction does not necessarily equate to under-estimating 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 under-predicted 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.
Abstract
We assess site-specific surface short-wave radiation forecasts from two high resolution configurations of the South African Weather Service numerical weather prediction model, at 4 km and 1.5 km. The models exhibit good skill overall in forecasting surface short-wave 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 over-prediction does not necessarily equate to under-estimating 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 under-predicted 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.
Abstract
The South Asian high (SAH) location and intensity are linked with the latent heating of the Tibetan Plateau (TP) and Yangtze River basin. The relationship between SAH variability and its impact on South Asian monsoon (SAM) onset is rarely linked with TP soil moisture. This study uses remotely sensed soil moisture and reanalysis products to quantify the relationship between the TP spring (April–June) soil moisture with SAH and SAM onset during 1988–2008. The results show that the TP spring soil moisture and monsoon onset indices are negatively correlated (R < −0.65), whereas the SAH exhibits a significant positive correlation (R ≥ 0.70) with TP soil moisture. The monsoon onset shows a difference of 20–25 days between the early- and late-onset composites. Significant positive (negative) soil moisture anomalies persist over the TP during the early (late) onset followed by positive (negative) LH (SH) anomalies during early (late)-onset composites. The TP thermal forcing exhibited positive anomalies during the early (late)-onset composites implying significant soil moisture control over the diabatic heating, which favors vertical ascent over the eastern plateau. Such a pattern leads to an earlier formation and movement of the SAH toward the Bay of Bengal (BOB) and southwestward of the TP. Before the early and late monsoon onset composites, the SAH pentad evolution drives the lower-tropospheric westerlies/easterlies toward continental SA. In the Indian Ocean the wind shear and transition from prevailing easterlies into westerlies during the pre-onset, onset, and post-onset pentad results in strong/weak ascent affecting the onset timing over the Arabian Sea and continental SA with less influence over the BOB monsoon onset.
Significance Statement
The Tibetan Plateau heating is one of the key drivers of the Asian monsoon precipitation in the surrounding regions, which has been previously studied in detail. This study explored the Tibetan Plateau spring soil moisture’s effect on South Asian monsoon onset timing. The monsoon onset timing is calculated using changes in wind direction, atmospheric temperature, and relative precipitation magnitude. Results found that the spring soil moisture substantially affects the TP thermal heating and the SA monsoon onset timing and highlights the physical processes leading to changes in the monsoon onset timing. The inclusion of soil moisture in estimating the monsoon onset timing can provide a tangible way of improving our understanding of the monsoon and associated water resources management practices.
Abstract
The South Asian high (SAH) location and intensity are linked with the latent heating of the Tibetan Plateau (TP) and Yangtze River basin. The relationship between SAH variability and its impact on South Asian monsoon (SAM) onset is rarely linked with TP soil moisture. This study uses remotely sensed soil moisture and reanalysis products to quantify the relationship between the TP spring (April–June) soil moisture with SAH and SAM onset during 1988–2008. The results show that the TP spring soil moisture and monsoon onset indices are negatively correlated (R < −0.65), whereas the SAH exhibits a significant positive correlation (R ≥ 0.70) with TP soil moisture. The monsoon onset shows a difference of 20–25 days between the early- and late-onset composites. Significant positive (negative) soil moisture anomalies persist over the TP during the early (late) onset followed by positive (negative) LH (SH) anomalies during early (late)-onset composites. The TP thermal forcing exhibited positive anomalies during the early (late)-onset composites implying significant soil moisture control over the diabatic heating, which favors vertical ascent over the eastern plateau. Such a pattern leads to an earlier formation and movement of the SAH toward the Bay of Bengal (BOB) and southwestward of the TP. Before the early and late monsoon onset composites, the SAH pentad evolution drives the lower-tropospheric westerlies/easterlies toward continental SA. In the Indian Ocean the wind shear and transition from prevailing easterlies into westerlies during the pre-onset, onset, and post-onset pentad results in strong/weak ascent affecting the onset timing over the Arabian Sea and continental SA with less influence over the BOB monsoon onset.
Significance Statement
The Tibetan Plateau heating is one of the key drivers of the Asian monsoon precipitation in the surrounding regions, which has been previously studied in detail. This study explored the Tibetan Plateau spring soil moisture’s effect on South Asian monsoon onset timing. The monsoon onset timing is calculated using changes in wind direction, atmospheric temperature, and relative precipitation magnitude. Results found that the spring soil moisture substantially affects the TP thermal heating and the SA monsoon onset timing and highlights the physical processes leading to changes in the monsoon onset timing. The inclusion of soil moisture in estimating the monsoon onset timing can provide a tangible way of improving our understanding of the monsoon and associated water resources management practices.
Abstract
The global positioning system dropwindsonde has provided thousands of high-resolution kinematic and thermodynamic soundings in and around tropical cyclones (TCs) since 1997. These data have revolutionized the understanding of TC structure, improved forecasts, and validated observations from remote sensing platforms. About 400 peer-reviewed studies on TCs using these data have been published to date. This paper reviews the history of dropwindsonde observations, changes to dropwindsonde technology since it was first used in TCs in 1982, and how the data have improved forecasting and changed our understanding of TCs.
Abstract
The global positioning system dropwindsonde has provided thousands of high-resolution kinematic and thermodynamic soundings in and around tropical cyclones (TCs) since 1997. These data have revolutionized the understanding of TC structure, improved forecasts, and validated observations from remote sensing platforms. About 400 peer-reviewed studies on TCs using these data have been published to date. This paper reviews the history of dropwindsonde observations, changes to dropwindsonde technology since it was first used in TCs in 1982, and how the data have improved forecasting and changed our understanding of TCs.
Abstract
Atmospheric science is male dominated and few students of color matriculate into the field, a trend dating back at least 50 years. UCAR/NCAR Equity and Inclusion (referred to as UNEION), which has trained nearly 200 employees, is the institution’s flagship diversity program. UNEION is central to efforts to create a welcoming workplace, engaging participants with peer-led learning to gain knowledge on diversity, equity, and inclusion (DEI) topics, and encouraging participants to implement these learnings through bystander intervention. Evaluation results show that UNEION 1) increases participants’ awareness of inequities, 2) encourages participants to feel responsible for DEI, and 3) teaches participants how to intervene in inappropriate situations.
Abstract
Atmospheric science is male dominated and few students of color matriculate into the field, a trend dating back at least 50 years. UCAR/NCAR Equity and Inclusion (referred to as UNEION), which has trained nearly 200 employees, is the institution’s flagship diversity program. UNEION is central to efforts to create a welcoming workplace, engaging participants with peer-led learning to gain knowledge on diversity, equity, and inclusion (DEI) topics, and encouraging participants to implement these learnings through bystander intervention. Evaluation results show that UNEION 1) increases participants’ awareness of inequities, 2) encourages participants to feel responsible for DEI, and 3) teaches participants how to intervene in inappropriate situations.
Abstract
On the local afternoon of 29 May 2012, a long-lived, right-moving (RM) supercell formed over northwestern Oklahoma and turned roughly southeastward. For >3 h, as it moved toward the Oklahoma City metro area, this supercell remained nontornadic and visually high-based, producing a nearly tornadic gustnado and a swath of significantly severe, sometimes giant hail up to 5 in (12.7 cm) in diameter. Meanwhile, a left-moving (LM) supercell formed over southwestern Oklahoma about 100 mi (161 km) south-southwest of the RM storm, and moved northeastward, with a rear-flank gust front that became well-defined on radar imagery as the LM storm approached southern and central parts of the metro. The authors, who had been observing the RM supercell in the field since genesis, surmised its potential future interaction with the LM storm’s trailing gust front about 1 h beforehand. We repositioned to near the gust front’s extrapolated collision point with the RM mesocyclone, in anticipation of maximized tornado potential, then witnessed a small tornado from the RM mesocyclone immediately following its interception of the boundary. Synchronized radar and photographic images of this remarkable sequence are presented and discussed in context of more recent findings on tornadic supercell/boundary interactions, with implications for operational utility.
Abstract
On the local afternoon of 29 May 2012, a long-lived, right-moving (RM) supercell formed over northwestern Oklahoma and turned roughly southeastward. For >3 h, as it moved toward the Oklahoma City metro area, this supercell remained nontornadic and visually high-based, producing a nearly tornadic gustnado and a swath of significantly severe, sometimes giant hail up to 5 in (12.7 cm) in diameter. Meanwhile, a left-moving (LM) supercell formed over southwestern Oklahoma about 100 mi (161 km) south-southwest of the RM storm, and moved northeastward, with a rear-flank gust front that became well-defined on radar imagery as the LM storm approached southern and central parts of the metro. The authors, who had been observing the RM supercell in the field since genesis, surmised its potential future interaction with the LM storm’s trailing gust front about 1 h beforehand. We repositioned to near the gust front’s extrapolated collision point with the RM mesocyclone, in anticipation of maximized tornado potential, then witnessed a small tornado from the RM mesocyclone immediately following its interception of the boundary. Synchronized radar and photographic images of this remarkable sequence are presented and discussed in context of more recent findings on tornadic supercell/boundary interactions, with implications for operational utility.
Abstract
The symmetries of the governing equations of atmospheric flows constrain the solutions. The present study applies those symmetries identified from the governing equations to the atmospheric boundary layers under relatively weak stratifications (stable and unstable). More specifically, the invariant solutions are analyzed, which conserve their forms under possible symmetry transformations of a governing–equation system. The key question is whether those invariant solutions can re–derive the known vertical profiles of both vertical fluxes and the means for the horizontal wind and the potential temperature. The mean profiles for the wind and the potential temperature in the surface layer predicted from the Monin–Obukhov theory can be recovered as invariant solutions. However, the consistent vertical fluxes both for the momentum and heat no longer remain constant with height, as assumed in the Monin–Obukhov theory, but linearly and parabolically change with height over the dynamic sublayer and the above, respectively, in stable conditions. The present study suggests that a deviation from the constancy, though observationally known to be weak, is a crucial part of the surface–layer dynamics to maintain its symmetry consistency.
Abstract
The symmetries of the governing equations of atmospheric flows constrain the solutions. The present study applies those symmetries identified from the governing equations to the atmospheric boundary layers under relatively weak stratifications (stable and unstable). More specifically, the invariant solutions are analyzed, which conserve their forms under possible symmetry transformations of a governing–equation system. The key question is whether those invariant solutions can re–derive the known vertical profiles of both vertical fluxes and the means for the horizontal wind and the potential temperature. The mean profiles for the wind and the potential temperature in the surface layer predicted from the Monin–Obukhov theory can be recovered as invariant solutions. However, the consistent vertical fluxes both for the momentum and heat no longer remain constant with height, as assumed in the Monin–Obukhov theory, but linearly and parabolically change with height over the dynamic sublayer and the above, respectively, in stable conditions. The present study suggests that a deviation from the constancy, though observationally known to be weak, is a crucial part of the surface–layer dynamics to maintain its symmetry consistency.
Abstract
This study focuses on the rainfall-producing weather systems in the southern Murray-Darling Basin (MDB), Australia. These weather systems are divided into objects: cyclones, fronts, anticyclones, warm conveyor belt (WCB) inflows, WCB ascents, potential vorticity (PV) streamers, and cut-off lows. We investigate the changes in the frequency, amplitude, and relative position of these objects as the daily and seasonal rainfall change. Days on which the rainfall is heavy, especially in winter, are characterized by more PV streamers, cut-off lows, cyclones, fronts and WCBs in the region. In contrast, dry days are characterized by more anticyclones over southeastern Australia in winter and summer.
The effect of upper-level weather objects (PV streamers and cut-off lows) on lower-level objects, and their importance in producing rainfall, is quantified using the quasi-geostrophic ω-equation and separating the vertical motion into that induced by the upper and lower levels. On heavy rainfall days in winter, PV streamers and cut-off lows force strong upward motion in the lower troposphere, promoting cyclogenesis at lower levels, forcing ascent in the WCBs, and producing rain downstream of the southern MDB. Lower-level ascent forced by upper-level objects is important for the development of heavy rainfall in both seasons, although particularly in winter.
Rainfall is attributed to individual objects. PV streamers and WCBs contribute most to the winter and summer rainfall respectively. The difference in rainfall between anomalously wet and dry years can be explained in winter by the changes in the rainfall associated with PV streamers, whereas in summer it is mostly due to a reduction in the rainfall associated with WCBs.
Abstract
This study focuses on the rainfall-producing weather systems in the southern Murray-Darling Basin (MDB), Australia. These weather systems are divided into objects: cyclones, fronts, anticyclones, warm conveyor belt (WCB) inflows, WCB ascents, potential vorticity (PV) streamers, and cut-off lows. We investigate the changes in the frequency, amplitude, and relative position of these objects as the daily and seasonal rainfall change. Days on which the rainfall is heavy, especially in winter, are characterized by more PV streamers, cut-off lows, cyclones, fronts and WCBs in the region. In contrast, dry days are characterized by more anticyclones over southeastern Australia in winter and summer.
The effect of upper-level weather objects (PV streamers and cut-off lows) on lower-level objects, and their importance in producing rainfall, is quantified using the quasi-geostrophic ω-equation and separating the vertical motion into that induced by the upper and lower levels. On heavy rainfall days in winter, PV streamers and cut-off lows force strong upward motion in the lower troposphere, promoting cyclogenesis at lower levels, forcing ascent in the WCBs, and producing rain downstream of the southern MDB. Lower-level ascent forced by upper-level objects is important for the development of heavy rainfall in both seasons, although particularly in winter.
Rainfall is attributed to individual objects. PV streamers and WCBs contribute most to the winter and summer rainfall respectively. The difference in rainfall between anomalously wet and dry years can be explained in winter by the changes in the rainfall associated with PV streamers, whereas in summer it is mostly due to a reduction in the rainfall associated with WCBs.
