Abstract
Climate change research must ensure international data comparability over long periods, and deep-ocean temperature measurements require accurate evaluation of thermometers because temperature changes there are small. We calibrated three reference thermometers (SBE 35) at the triple point of water and the gallium melting point, as defined by the International Temperature Scale of 1990, and confirmed that they were extremely stable over a 20-year period; the temporal drift for two of the three was within ±0.2 mK decade−1. We evaluated the pressure sensitivities of two conductivity-temperature-depth (CTD) thermometers in a laboratory up to 68 MPa; the results agreed with values estimated using SBE 35s in the deep ocean. We evaluated temperature hysteresis of the three SBE 35s in the laboratory; one showed no hysteresis, and the other two exhibited hysteresis of 0.3–0.5 mK. Pressure hysteresis was examined in the deep ocean. Of 22 CTD thermometers, more than half showed estimated pressure hysteresis of 0.5–1 mK. The overall expanded uncertainty of the deep ocean temperature measurement (depths greater than 20 MPa) by the CTD thermometer with small hysteresis calibrated in reference to the SBE 35 is estimated to be 0.8 mK To eliminate the influence of systematic errors due to hysteresis, we strongly recommend aligning the temperature data 0.3 seconds ahead of the pressure data to account for the temperature data delay due to the sensor’s response time, and applying the in situ calibration coefficients obtained from up-cast data to the continuous up-cast profile, thereby modifying both continuous profile data and data from discrete water sampling depths from the up-cast.
Abstract
Climate change research must ensure international data comparability over long periods, and deep-ocean temperature measurements require accurate evaluation of thermometers because temperature changes there are small. We calibrated three reference thermometers (SBE 35) at the triple point of water and the gallium melting point, as defined by the International Temperature Scale of 1990, and confirmed that they were extremely stable over a 20-year period; the temporal drift for two of the three was within ±0.2 mK decade−1. We evaluated the pressure sensitivities of two conductivity-temperature-depth (CTD) thermometers in a laboratory up to 68 MPa; the results agreed with values estimated using SBE 35s in the deep ocean. We evaluated temperature hysteresis of the three SBE 35s in the laboratory; one showed no hysteresis, and the other two exhibited hysteresis of 0.3–0.5 mK. Pressure hysteresis was examined in the deep ocean. Of 22 CTD thermometers, more than half showed estimated pressure hysteresis of 0.5–1 mK. The overall expanded uncertainty of the deep ocean temperature measurement (depths greater than 20 MPa) by the CTD thermometer with small hysteresis calibrated in reference to the SBE 35 is estimated to be 0.8 mK To eliminate the influence of systematic errors due to hysteresis, we strongly recommend aligning the temperature data 0.3 seconds ahead of the pressure data to account for the temperature data delay due to the sensor’s response time, and applying the in situ calibration coefficients obtained from up-cast data to the continuous up-cast profile, thereby modifying both continuous profile data and data from discrete water sampling depths from the up-cast.
Abstract
The U.S. Department of Agriculture National Agricultural Statistics Service (NASS) collects crop soil (top-soil and subsoil) moisture conditions in U.S. agricultural regions. NASS dynamically assesses crop soil moisture conditions in four categories—very short, short, adequate, and surplus, and publishes weekly statistics for states. Previous studies mapped NASS crop soil moisture (SM) condition categories to NASA’s Soil Moisture Active Passive (SMAP) L4 weekly surface and rootzone soil moisture by using NASS survey-reported category percentages to determine corresponding threshold values from the cumulative distributions of SMAP soil moisture. However, a notable challenge arose in croplands with coarse-textured soils, where frequent irrigation is necessary due to rapid drainage. Yet, the SMAP product often inaccurately indicates dry conditions in these soils, failing to capture the effects of irrigation due to coarse resolution and mixed pixel. To address this issue, this study utilizes soil moisture anomalies to better reflect crop soil moisture conditions in irrigated lands. Soil moisture anomalies were categorized into the same four classes, with classification thresholds determined by mapping cumulative distributions of SMAP surface and rootzone anomalies to NASS categories. We compared SMAP SM-based with SMAP anomaly-based estimates for the soil moisture conditions in two case study regions: the Columbia Basin in Washington (which includes irrigated and non-irrigated croplands) and Iowa (primarily non-irrigated), followed by an uncertainty analysis of the anomaly-based results. The key finding is that anomaly-based mapping yields a different and more distinct representation of soil moisture conditions for irrigated versus non-irrigated croplands in Washington’s Columbia Basin during a drought year.
Abstract
The U.S. Department of Agriculture National Agricultural Statistics Service (NASS) collects crop soil (top-soil and subsoil) moisture conditions in U.S. agricultural regions. NASS dynamically assesses crop soil moisture conditions in four categories—very short, short, adequate, and surplus, and publishes weekly statistics for states. Previous studies mapped NASS crop soil moisture (SM) condition categories to NASA’s Soil Moisture Active Passive (SMAP) L4 weekly surface and rootzone soil moisture by using NASS survey-reported category percentages to determine corresponding threshold values from the cumulative distributions of SMAP soil moisture. However, a notable challenge arose in croplands with coarse-textured soils, where frequent irrigation is necessary due to rapid drainage. Yet, the SMAP product often inaccurately indicates dry conditions in these soils, failing to capture the effects of irrigation due to coarse resolution and mixed pixel. To address this issue, this study utilizes soil moisture anomalies to better reflect crop soil moisture conditions in irrigated lands. Soil moisture anomalies were categorized into the same four classes, with classification thresholds determined by mapping cumulative distributions of SMAP surface and rootzone anomalies to NASS categories. We compared SMAP SM-based with SMAP anomaly-based estimates for the soil moisture conditions in two case study regions: the Columbia Basin in Washington (which includes irrigated and non-irrigated croplands) and Iowa (primarily non-irrigated), followed by an uncertainty analysis of the anomaly-based results. The key finding is that anomaly-based mapping yields a different and more distinct representation of soil moisture conditions for irrigated versus non-irrigated croplands in Washington’s Columbia Basin during a drought year.
Abstract
The Madden–Julian oscillation (MJO) is a dominant intraseasonal variability of tropical convective activity characterized by its eastward propagation over the Indo-Pacific sector. By using observational and reanalysis datasets, this study investigates how the intraseasonal MJO activity is modulated by interannual variability of the Australian summer monsoon that peaks in January and February. Under the weak monsoon, the MJO activity tends to be stronger and propagates across the Maritime Continent farther eastward into the central Pacific. Under the strong monsoon, in contrast, the MJO activity tends to be weaker with its eastward propagation disrupted around the Maritime Continent. These MJO modulations tend to lag the anomalous monsoon intensity by about a month and then continue into March. Possible mechanisms are examined through a moist static energy budget analysis. Weaker monsoon with a dryer condition around northern Australia enhances the horizontal moisture gradient over the tropical western Pacific and thereby intensifies intraseasonal moistening or drying through the horizontal advection associated with the MJO, which promotes the eastward propagation of the MJO. Once the anomalous MJO convection reaches the central Pacific, it forces intraseasonal wind anomalies in the reversed direction over the western Pacific in the weaker monsoon condition. The resultant enhancement of drying or moistening by the horizontal advection again reinforces the eastward propagation. Wind–evaporation feedback associated with submonthly disturbances may also act to maintain the MJO convection northwest of Australia in the weak Australian monsoon years.
Significance Statement
The Madden–Julian oscillation (MJO) is a dominant subseasonal variability of the tropical atmosphere that propagates eastward over the Indo-Pacific sector. Meanwhile, year-to-year variability of the Australian monsoon is a major stationary variability of tropical convection in austral summer. This study reveals how the seasonal intensity of the Australian summer monsoon modulates the MJO; the weak Australian monsoon leads to stronger MJO activity and its eastward propagation and vice versa. Possible mechanisms are investigated through a moist static energy budget analysis. The monsoonal modulations in water vapor distribution and sea surface evaporation around northern Australia are found to regulate the eastward propagation and amplitude of the MJO.
Abstract
The Madden–Julian oscillation (MJO) is a dominant intraseasonal variability of tropical convective activity characterized by its eastward propagation over the Indo-Pacific sector. By using observational and reanalysis datasets, this study investigates how the intraseasonal MJO activity is modulated by interannual variability of the Australian summer monsoon that peaks in January and February. Under the weak monsoon, the MJO activity tends to be stronger and propagates across the Maritime Continent farther eastward into the central Pacific. Under the strong monsoon, in contrast, the MJO activity tends to be weaker with its eastward propagation disrupted around the Maritime Continent. These MJO modulations tend to lag the anomalous monsoon intensity by about a month and then continue into March. Possible mechanisms are examined through a moist static energy budget analysis. Weaker monsoon with a dryer condition around northern Australia enhances the horizontal moisture gradient over the tropical western Pacific and thereby intensifies intraseasonal moistening or drying through the horizontal advection associated with the MJO, which promotes the eastward propagation of the MJO. Once the anomalous MJO convection reaches the central Pacific, it forces intraseasonal wind anomalies in the reversed direction over the western Pacific in the weaker monsoon condition. The resultant enhancement of drying or moistening by the horizontal advection again reinforces the eastward propagation. Wind–evaporation feedback associated with submonthly disturbances may also act to maintain the MJO convection northwest of Australia in the weak Australian monsoon years.
Significance Statement
The Madden–Julian oscillation (MJO) is a dominant subseasonal variability of the tropical atmosphere that propagates eastward over the Indo-Pacific sector. Meanwhile, year-to-year variability of the Australian monsoon is a major stationary variability of tropical convection in austral summer. This study reveals how the seasonal intensity of the Australian summer monsoon modulates the MJO; the weak Australian monsoon leads to stronger MJO activity and its eastward propagation and vice versa. Possible mechanisms are investigated through a moist static energy budget analysis. The monsoonal modulations in water vapor distribution and sea surface evaporation around northern Australia are found to regulate the eastward propagation and amplitude of the MJO.
Abstract
The lower-level western North Pacific subtropical high (WPH) exerts a significant influence on the water vapor transportation, while the upper-level East Asian subtropical jet (EAJ) contributes to vertical motion through the secondary circulation in the jet–streak exit region. Together, these two circulation systems serve as the primary determinants of the spatial distribution and intensity of monsoonal rainfall, thereby shaping intraseasonal precipitation anomalies over eastern China. Building upon this physical understanding, we define three critical circulation indices: the meridional displacement index of the EAJ, the intensity index of the EAJ, and the pattern index of the WPH. The meridional displacement of the EAJ is influenced by intraseasonal Rossby wave trains propagating along the Africa–Asia subtropical westerly jet stream, which is associated with convection in the tropical Indian Ocean. In contrast, the intensity of the EAJ is predominantly determined by intraseasonal Rossby wave trains originating from northern Europe and propagating toward East Asia. The combined effects of EAJ meridional displacements and changes in the WPH pattern contribute to significant north–south migrations of rainfall belts across eastern China. Conversely, variations in the intensity of the EAJ, together with alterations in the WPH pattern, control the intensity of rainfall anomalies in the Yangtze River basin. The various combos of EAJ and WPH provide a basis for understanding and predicting intraseasonal rainfall variability in eastern China during flooding season.
Significance Statement
The upper-level East Asian subtropical jet (EAJ) and lower-level western North Pacific subtropical high (WPH) are critical circulation systems influencing precipitation anomalies over eastern China during the flood season. However, the dynamics underpinning the varying configurations of these systems and their distinct impacts on 10–40-day precipitation anomalies are not yet fully understood. Here, we show that combinations of the EAJ meridional displacements and the WPH pattern changes govern north–south swings of precipitation anomalies over eastern China, whereas combinations of the EAJ intensity variations and the WPH pattern changes modulate rainfall intensity in the Yangtze River basin. By leveraging these identified physical connections, we propose two sets of circulation indices aimed at enhancing the monitoring and predictive capabilities of intraseasonal precipitation over eastern China during the flood season.
Abstract
The lower-level western North Pacific subtropical high (WPH) exerts a significant influence on the water vapor transportation, while the upper-level East Asian subtropical jet (EAJ) contributes to vertical motion through the secondary circulation in the jet–streak exit region. Together, these two circulation systems serve as the primary determinants of the spatial distribution and intensity of monsoonal rainfall, thereby shaping intraseasonal precipitation anomalies over eastern China. Building upon this physical understanding, we define three critical circulation indices: the meridional displacement index of the EAJ, the intensity index of the EAJ, and the pattern index of the WPH. The meridional displacement of the EAJ is influenced by intraseasonal Rossby wave trains propagating along the Africa–Asia subtropical westerly jet stream, which is associated with convection in the tropical Indian Ocean. In contrast, the intensity of the EAJ is predominantly determined by intraseasonal Rossby wave trains originating from northern Europe and propagating toward East Asia. The combined effects of EAJ meridional displacements and changes in the WPH pattern contribute to significant north–south migrations of rainfall belts across eastern China. Conversely, variations in the intensity of the EAJ, together with alterations in the WPH pattern, control the intensity of rainfall anomalies in the Yangtze River basin. The various combos of EAJ and WPH provide a basis for understanding and predicting intraseasonal rainfall variability in eastern China during flooding season.
Significance Statement
The upper-level East Asian subtropical jet (EAJ) and lower-level western North Pacific subtropical high (WPH) are critical circulation systems influencing precipitation anomalies over eastern China during the flood season. However, the dynamics underpinning the varying configurations of these systems and their distinct impacts on 10–40-day precipitation anomalies are not yet fully understood. Here, we show that combinations of the EAJ meridional displacements and the WPH pattern changes govern north–south swings of precipitation anomalies over eastern China, whereas combinations of the EAJ intensity variations and the WPH pattern changes modulate rainfall intensity in the Yangtze River basin. By leveraging these identified physical connections, we propose two sets of circulation indices aimed at enhancing the monitoring and predictive capabilities of intraseasonal precipitation over eastern China during the flood season.
Abstract
Severe convective storms (SCSs) pose significant hazards, and understanding their potential evolution under climate change is crucial. This study investigates projected changes in SCS environments over the contiguous United States using the Max Planck Institute Earth System Model, version 1.2, high resolution (MPI-ESM1.2-HR) under the shared socioeconomic pathway (SSP) 3-7.0 scenario. We analyze vertical atmospheric profiles from historical (1990–2009) and future (2080–99) simulations, focusing on soundings with 0–6-km wind shear ≥ 15 m s−1 and various ranges of mixed-layer entraining CAPE (ECAPE). Clustering analysis using a 4 × 4 self-organizing map (SOM) is performed on normalized virtual buoyancy and rotated wind profiles from both periods combined, allowing for a direct comparison of environments. Results indicate a projected increase in both the annual frequency and spatial extent of environments conducive to SCS across all ECAPE categories, particularly for higher ECAPE values. Spatial analysis reveals a shift away from the central Great Plains for low-ECAPE environments, while medium- and high-ECAPE environments show widespread increases, especially over the central and eastern United States. High supercell composite parameter (SCP) SOM nodes exhibit significant future increases in thermodynamic instability and equilibrium level heights, alongside increased convective inhibition and cloud-base heights and decreased low-level relative humidity. The fundamental structure of soundings within SOM nodes appears consistent between periods, suggesting that changes are primarily in the frequency of these environmental types. Seasonally, a more intense and potentially earlier peak activity period (spring/summer) is projected for high-SCP environments. These findings suggest an increased potential for environments supporting severe convection in a future warmer climate.
Significance Statement
As the climate warms, the atmospheric conditions that fuel severe thunderstorms are projected to change significantly. This study uses a climate model and a novel classification method to reveal what type of potential severe weather favorable environments will become more frequent, widespread, and intense. The most extreme of these environments show the largest relative percentage increases. Critically, the risk is projected to expand beyond the traditional “Tornado Alley,” and the severe weather season is starting earlier and becoming more concentrated. These findings signal a growing threat to lives and property across a broader portion of the nation, highlighting the need to reassess and enhance our societal preparedness for severe weather.
Abstract
Severe convective storms (SCSs) pose significant hazards, and understanding their potential evolution under climate change is crucial. This study investigates projected changes in SCS environments over the contiguous United States using the Max Planck Institute Earth System Model, version 1.2, high resolution (MPI-ESM1.2-HR) under the shared socioeconomic pathway (SSP) 3-7.0 scenario. We analyze vertical atmospheric profiles from historical (1990–2009) and future (2080–99) simulations, focusing on soundings with 0–6-km wind shear ≥ 15 m s−1 and various ranges of mixed-layer entraining CAPE (ECAPE). Clustering analysis using a 4 × 4 self-organizing map (SOM) is performed on normalized virtual buoyancy and rotated wind profiles from both periods combined, allowing for a direct comparison of environments. Results indicate a projected increase in both the annual frequency and spatial extent of environments conducive to SCS across all ECAPE categories, particularly for higher ECAPE values. Spatial analysis reveals a shift away from the central Great Plains for low-ECAPE environments, while medium- and high-ECAPE environments show widespread increases, especially over the central and eastern United States. High supercell composite parameter (SCP) SOM nodes exhibit significant future increases in thermodynamic instability and equilibrium level heights, alongside increased convective inhibition and cloud-base heights and decreased low-level relative humidity. The fundamental structure of soundings within SOM nodes appears consistent between periods, suggesting that changes are primarily in the frequency of these environmental types. Seasonally, a more intense and potentially earlier peak activity period (spring/summer) is projected for high-SCP environments. These findings suggest an increased potential for environments supporting severe convection in a future warmer climate.
Significance Statement
As the climate warms, the atmospheric conditions that fuel severe thunderstorms are projected to change significantly. This study uses a climate model and a novel classification method to reveal what type of potential severe weather favorable environments will become more frequent, widespread, and intense. The most extreme of these environments show the largest relative percentage increases. Critically, the risk is projected to expand beyond the traditional “Tornado Alley,” and the severe weather season is starting earlier and becoming more concentrated. These findings signal a growing threat to lives and property across a broader portion of the nation, highlighting the need to reassess and enhance our societal preparedness for severe weather.
Abstract
Recent research has shown that the rating frequency for intense tornadoes (rated ≥EF3 on the Enhanced Fujita or EF scale) dating back to 2014 is at a historical low relative to both the real-time Fujita-Scale rating era (1977–2006) and the early years of the EF-scale rating era (2007–2013, with or without the catastrophic 2011 tornado season). However, with no formal change in National Weather Service directives on rating tornadoes or significant changes to the EF scale applied in the 2013–2014 timeframe, the cause for this sudden decrease in intense-tornado frequency is unclear. This study investigates intense-tornado rating determinations from 2014–2024 to ascertain some potential causes for this sudden downturn in intense-tornado ratings, by comparing how instances of damage are evaluated on the EF scale to their likely evaluation using the legacy Fujita Scale. We find that a series of factors, both intrinsic to the current operational EF scale and related to how it is being applied, has likely contributed to the downshift in intense-tornado ratings. The evaluation of damage associated with indicators that are unique to the EF scale is too infrequent at higher damage intensities to overcome these factors. Given these findings, we suggest that a reanalysis effort for the significant-tornado [(E)F2 or greater] record should be undertaken upon any future operational adoption of a revised EF scale to develop a more consistent intense-tornado record in the United States.
Abstract
Recent research has shown that the rating frequency for intense tornadoes (rated ≥EF3 on the Enhanced Fujita or EF scale) dating back to 2014 is at a historical low relative to both the real-time Fujita-Scale rating era (1977–2006) and the early years of the EF-scale rating era (2007–2013, with or without the catastrophic 2011 tornado season). However, with no formal change in National Weather Service directives on rating tornadoes or significant changes to the EF scale applied in the 2013–2014 timeframe, the cause for this sudden decrease in intense-tornado frequency is unclear. This study investigates intense-tornado rating determinations from 2014–2024 to ascertain some potential causes for this sudden downturn in intense-tornado ratings, by comparing how instances of damage are evaluated on the EF scale to their likely evaluation using the legacy Fujita Scale. We find that a series of factors, both intrinsic to the current operational EF scale and related to how it is being applied, has likely contributed to the downshift in intense-tornado ratings. The evaluation of damage associated with indicators that are unique to the EF scale is too infrequent at higher damage intensities to overcome these factors. Given these findings, we suggest that a reanalysis effort for the significant-tornado [(E)F2 or greater] record should be undertaken upon any future operational adoption of a revised EF scale to develop a more consistent intense-tornado record in the United States.
Abstract
On 4 July 2025, multiple factors combined to produce a catastrophic flash flood in the Texas Hill Country. The event caused 137 fatalities across South Texas, with the greatest impacts in Kerr County (119 fatalities with two additional missing persons) near the Camp Mystic for Girls summer camp. Widespread convection occurred across the Texas Hill Country, including a focused ten-county area that received >150 mm of rainfall between 0300 and 1800 UTC, while a quasi-stationary supercell generated localized totals >250 mm largely within a 3-h period from 0600 to 0900 UTC over the Guadalupe River basin headwaters. This study synthesizes observations, reanalyses, convection-allowing model analyses, and hydrologic simulations to diagnose the event. Results show that the supercell formed as a northwestward-moving surface boundary intersected strengthening midlevel westerly flow on the southern flank of a mesoscale convective vortex that tracked from northern Mexico into south-central Texas. Increasing southwesterly flow aloft and a strengthening southeasterly low-level jet enhanced vertical shear, supporting supercell organization and limited storm motion. Deep tropical moisture from the southeast, modulated by Tropical Cyclone Barry, together with mid- and upper-level moisture from the tropical eastern North Pacific associated with Tropical Cyclone Flossie, promoted high precipitation efficiency and extreme rain rates. Hydrologic simulations indicate that storm placement over the basin promoted near-synchronous flood-wave superposition from the South Fork of the Guadalupe River and Cypress Creek at Camp Mystic, exacerbating inundation. A companion study examines short-term predictability using convection-allowing ensemble forecasts coupled with hydrologic prediction tools.
Abstract
On 4 July 2025, multiple factors combined to produce a catastrophic flash flood in the Texas Hill Country. The event caused 137 fatalities across South Texas, with the greatest impacts in Kerr County (119 fatalities with two additional missing persons) near the Camp Mystic for Girls summer camp. Widespread convection occurred across the Texas Hill Country, including a focused ten-county area that received >150 mm of rainfall between 0300 and 1800 UTC, while a quasi-stationary supercell generated localized totals >250 mm largely within a 3-h period from 0600 to 0900 UTC over the Guadalupe River basin headwaters. This study synthesizes observations, reanalyses, convection-allowing model analyses, and hydrologic simulations to diagnose the event. Results show that the supercell formed as a northwestward-moving surface boundary intersected strengthening midlevel westerly flow on the southern flank of a mesoscale convective vortex that tracked from northern Mexico into south-central Texas. Increasing southwesterly flow aloft and a strengthening southeasterly low-level jet enhanced vertical shear, supporting supercell organization and limited storm motion. Deep tropical moisture from the southeast, modulated by Tropical Cyclone Barry, together with mid- and upper-level moisture from the tropical eastern North Pacific associated with Tropical Cyclone Flossie, promoted high precipitation efficiency and extreme rain rates. Hydrologic simulations indicate that storm placement over the basin promoted near-synchronous flood-wave superposition from the South Fork of the Guadalupe River and Cypress Creek at Camp Mystic, exacerbating inundation. A companion study examines short-term predictability using convection-allowing ensemble forecasts coupled with hydrologic prediction tools.
Abstract
The three-way Ekman balance of Coriolis, pressure gradient and drag forces is an established starting point for understanding the structure of boundary-layer winds in mid-latitude cyclones. The addition of advection gives a more representative momentum balance. It also provides a helpful way to understand the problem of physics-dynamics coupling in weather and climate models. Bannon (1998) compared several models including advection within the Ekman spiral. One of the most accurate models was the Ekman momentum model. Since then, we have introduced the Semigeotriptic model that modifies the friction term in the Ekman momentum model to give a robust negative definite energy evolution. This property gives the Semigeotriptic model applicability to a larger range of time-varying flows than the Ekman momentum model. However, there is still the need to evaluate its accuracy. Using the same equilibrium framework as Bannon (1998), we show that the Semigeotriptic model is consistent with the other models. All the models change the wind turning, decreasing it at positive Rossby number and increasing it for negative values. We then evaluate the impact of the Bannon (1998) models and the Semigeotriptic model using a parametrization in an idealised quasi-geostrophic cyclone lifecycle. All the models that include equilibrium advection produce a deepening (of order 1.7 hPa) of the mid-latitude cyclone over 48 hours. This change is related to the reduced Ekman pumping.
Abstract
The three-way Ekman balance of Coriolis, pressure gradient and drag forces is an established starting point for understanding the structure of boundary-layer winds in mid-latitude cyclones. The addition of advection gives a more representative momentum balance. It also provides a helpful way to understand the problem of physics-dynamics coupling in weather and climate models. Bannon (1998) compared several models including advection within the Ekman spiral. One of the most accurate models was the Ekman momentum model. Since then, we have introduced the Semigeotriptic model that modifies the friction term in the Ekman momentum model to give a robust negative definite energy evolution. This property gives the Semigeotriptic model applicability to a larger range of time-varying flows than the Ekman momentum model. However, there is still the need to evaluate its accuracy. Using the same equilibrium framework as Bannon (1998), we show that the Semigeotriptic model is consistent with the other models. All the models change the wind turning, decreasing it at positive Rossby number and increasing it for negative values. We then evaluate the impact of the Bannon (1998) models and the Semigeotriptic model using a parametrization in an idealised quasi-geostrophic cyclone lifecycle. All the models that include equilibrium advection produce a deepening (of order 1.7 hPa) of the mid-latitude cyclone over 48 hours. This change is related to the reduced Ekman pumping.
Abstract
This study evaluates the impact of the Stochastic Kinetic Energy Backscatter (SKEB) scheme on forecast skill within the Navy Earth System Prediction Capability (Navy ESPC). A control version of the Navy ESPC 30-day ensemble is compared against a version with SKEB. The performance is assessed using standard metrics, kinetic energy (KE) spectral density, and forecast skill for the Madden-Julian Oscillation (MJO).
The results demonstrate that SKEB helps reduce the underdispersion seen in Navy ESPC by increasing the standard deviations (STDV) in the ensemble. SKEB also statistically significantly reduces the Root Mean Square Error (RMSE) and bias for key atmospheric and oceanic variables. Outgoing longwave radiation showed the most robust response to SKEB, with significant improvements in bias, RMSE, and variability maintained throughout the 30-day period globally and regionally.
KE spectra analysis reveals SKEB introduces small-scale perturbations with largest impact at planetary scales by day 1. This work shows that the inclusion of SKEB improves the prediction system by introducing more realistic variability across a spectrum of spatial scales. This yields a more skillful ensemble with reduced systematic errors, confirming stochastic perturbations' value for subseasonal forecasting.
Ultimately, our findings demonstrate that SKEB improvements in forecast skill extend beyond the atmospheric component to the coupled ocean-atmosphere system. Despite stochastic perturbations being applied only to the atmospheric component, corrections propagate throughout the coupled model, enhancing predictive accuracy in both model components. This cross-component improvement underscores the potential of stochastic perturbations to advance Earth system prediction capabilities across multiple domains on weather and subseasonal scales.
Abstract
This study evaluates the impact of the Stochastic Kinetic Energy Backscatter (SKEB) scheme on forecast skill within the Navy Earth System Prediction Capability (Navy ESPC). A control version of the Navy ESPC 30-day ensemble is compared against a version with SKEB. The performance is assessed using standard metrics, kinetic energy (KE) spectral density, and forecast skill for the Madden-Julian Oscillation (MJO).
The results demonstrate that SKEB helps reduce the underdispersion seen in Navy ESPC by increasing the standard deviations (STDV) in the ensemble. SKEB also statistically significantly reduces the Root Mean Square Error (RMSE) and bias for key atmospheric and oceanic variables. Outgoing longwave radiation showed the most robust response to SKEB, with significant improvements in bias, RMSE, and variability maintained throughout the 30-day period globally and regionally.
KE spectra analysis reveals SKEB introduces small-scale perturbations with largest impact at planetary scales by day 1. This work shows that the inclusion of SKEB improves the prediction system by introducing more realistic variability across a spectrum of spatial scales. This yields a more skillful ensemble with reduced systematic errors, confirming stochastic perturbations' value for subseasonal forecasting.
Ultimately, our findings demonstrate that SKEB improvements in forecast skill extend beyond the atmospheric component to the coupled ocean-atmosphere system. Despite stochastic perturbations being applied only to the atmospheric component, corrections propagate throughout the coupled model, enhancing predictive accuracy in both model components. This cross-component improvement underscores the potential of stochastic perturbations to advance Earth system prediction capabilities across multiple domains on weather and subseasonal scales.
