Pub Date : 2023-07-24DOI: 10.1175/jtech-d-23-0052.1
D. Chelton
The ability to estimate surface current divergence and vorticity from space is assessed from simulated satellite Doppler radar scatterometer measurements of surface velocity with an effective footprint diameter of 5 km across an 1800-km measurement swath. The focus is on non-internal-wave contributions to divergence and vorticity. This is achieved by simulating Doppler measurements of surface velocity from a numerical model in which internal waves are weak because of high dissipation, seasonal cycle forcing and the lack of tidal forcing. Divergence is much more challenging to estimate than vorticity because the signals are weaker and restricted to smaller scales. With the measurement noise that was anticipated based on early engineering studies, divergence cannot be estimated with useful resolution. Recent advances in the understanding of how the noise in measurements of surface currents depends on the ambient wind speed have concluded that measurement noise will be substantially smaller in conditions of wind speed greater than 6 m s−1. A reassessment of the ability to estimate non-internal-wave contributions to surface current divergence in this study finds that useful estimates can be obtained in such wind conditions; the wavelength resolution capability for divergence estimates in the middle of the measurement swaths will be better than 100 km in 16-day averages. The improved measurement accuracy will also provide estimates of surface current vorticity with a resolution nearly a factor-of-2 higher than was previously thought, resulting in wavelength resolutions of about 50 km, 30 km and 20 km in snapshots, 4-day averages and 16-day averages, respectively.
通过模拟卫星多普勒雷达散射仪对1800公里测量带上有效足迹直径为5公里的表面速度的测量，评估了从空间估计表面电流散度和涡度的能力。重点是非内波对散度和涡度的贡献。这是通过模拟数值模型中表面速度的多普勒测量来实现的，在该模型中，由于高耗散、季节性周期强迫和缺乏潮汐强迫，内波较弱。散度比涡度更难估计，因为信号较弱，并且局限于较小的尺度。由于测量噪声是基于早期工程研究预期的，因此无法用有用的分辨率来估计偏差。在理解表面电流测量中的噪声如何取决于环境风速方面的最新进展表明，在风速大于6 m s−1的情况下，测量噪声将显著较小。在这项研究中，对估计非内波对地表电流发散的贡献的能力进行了重新评估，发现在这种风况下可以获得有用的估计；在16天的平均值中，测量带中间的发散估计的波长分辨率能力将优于100km。测量精度的提高还将提供表面流涡度的估计，其分辨率比之前认为的高出近2倍，从而在快照、4天平均值和16天平均值中分别获得约50公里、30公里和20公里的波长分辨率。
{"title":"Estimation of Surface Current Divergence from Satellite Doppler Radar Scatterometer Measurements of Surface Ocean Velocity","authors":"D. Chelton","doi":"10.1175/jtech-d-23-0052.1","DOIUrl":"https://doi.org/10.1175/jtech-d-23-0052.1","url":null,"abstract":"\u0000The ability to estimate surface current divergence and vorticity from space is assessed from simulated satellite Doppler radar scatterometer measurements of surface velocity with an effective footprint diameter of 5 km across an 1800-km measurement swath. The focus is on non-internal-wave contributions to divergence and vorticity. This is achieved by simulating Doppler measurements of surface velocity from a numerical model in which internal waves are weak because of high dissipation, seasonal cycle forcing and the lack of tidal forcing. Divergence is much more challenging to estimate than vorticity because the signals are weaker and restricted to smaller scales. With the measurement noise that was anticipated based on early engineering studies, divergence cannot be estimated with useful resolution. Recent advances in the understanding of how the noise in measurements of surface currents depends on the ambient wind speed have concluded that measurement noise will be substantially smaller in conditions of wind speed greater than 6 m s−1. A reassessment of the ability to estimate non-internal-wave contributions to surface current divergence in this study finds that useful estimates can be obtained in such wind conditions; the wavelength resolution capability for divergence estimates in the middle of the measurement swaths will be better than 100 km in 16-day averages. The improved measurement accuracy will also provide estimates of surface current vorticity with a resolution nearly a factor-of-2 higher than was previously thought, resulting in wavelength resolutions of about 50 km, 30 km and 20 km in snapshots, 4-day averages and 16-day averages, respectively.","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45319269","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-21DOI: 10.1175/jtech-d-22-0120.1
Daile Zhang, K. Cummins, T. Lang, D. Buechler, S. Rudlosky
Optical lightning observations from low-Earth orbit play an important role in our understanding of long-term global lightning trends. Lightning Imaging Sensors (LIS) on the Tropical Rainfall Measurement Mission (TRMM) satellite (1997-2015) and International Space Station (2017-present) capture optical emissions produced by lightning. This study uses the well-documented TRMM LIS performance to determine if the ISS LIS performs well enough to bridge the gap between TRMM LIS and the new generation of Geostationary Lightning Mappers (GLMs). The average events per group and groups per flash for ISS LIS are 3.6 and 9.9, which are 25% and 10% lower than TRMM LIS, respectively. ISS LIS has 30% lower mean group energy density and 30-50% lower mean flash energy density than TRMM LIS in their common (+/−38 degree) latitude range. These differences are likely the result of larger pixel areas for ISS LIS over most of the field-of-view due to off-nadir pointing, combined with viewing obstructions and possible engineering differences. For both instruments, radiometric sensitivity decreases radially from the center of the array to the edges. ISS LIS sensitivity falls-off faster and more-variably, contributed to by the off-nadir pointing. Event energy density analysis indicate some anomalous hotspot pixels in the ISS LIS pixel array that were not present with the TRMM LIS. Despite these differences, ISS LIS provides similar parameter values to TRMM LIS with the expectation of somewhat lower lightning detection capability. In addition, recalculation of the event, group, and flash areas for both LIS datasets are strongly recommended since the archived values in the current release versions have significant errors.
{"title":"Performance Evaluation of the Lightning Imaging Sensor on the International Space Station","authors":"Daile Zhang, K. Cummins, T. Lang, D. Buechler, S. Rudlosky","doi":"10.1175/jtech-d-22-0120.1","DOIUrl":"https://doi.org/10.1175/jtech-d-22-0120.1","url":null,"abstract":"\u0000Optical lightning observations from low-Earth orbit play an important role in our understanding of long-term global lightning trends. Lightning Imaging Sensors (LIS) on the Tropical Rainfall Measurement Mission (TRMM) satellite (1997-2015) and International Space Station (2017-present) capture optical emissions produced by lightning. This study uses the well-documented TRMM LIS performance to determine if the ISS LIS performs well enough to bridge the gap between TRMM LIS and the new generation of Geostationary Lightning Mappers (GLMs). The average events per group and groups per flash for ISS LIS are 3.6 and 9.9, which are 25% and 10% lower than TRMM LIS, respectively. ISS LIS has 30% lower mean group energy density and 30-50% lower mean flash energy density than TRMM LIS in their common (+/−38 degree) latitude range. These differences are likely the result of larger pixel areas for ISS LIS over most of the field-of-view due to off-nadir pointing, combined with viewing obstructions and possible engineering differences. For both instruments, radiometric sensitivity decreases radially from the center of the array to the edges. ISS LIS sensitivity falls-off faster and more-variably, contributed to by the off-nadir pointing. Event energy density analysis indicate some anomalous hotspot pixels in the ISS LIS pixel array that were not present with the TRMM LIS. Despite these differences, ISS LIS provides similar parameter values to TRMM LIS with the expectation of somewhat lower lightning detection capability. In addition, recalculation of the event, group, and flash areas for both LIS datasets are strongly recommended since the archived values in the current release versions have significant errors.","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"64665998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-20DOI: 10.1175/jtech-d-22-0106.1
Yanling Wu, Youmin Tang
A retrospective tropical Indian Ocean Dipole mode (IOD) hindcast for 1958–2014 was conducted using 20 models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), with a model-based analog forecast (MAF) method. In the MAF approach, forecast ensembles are extracted from preexisting model simulations by finding the states that initially best match an observed anomaly and tracking their subsequent evolution, with no additional model integrations. By optimizing the key factors in the MAF method, we suggest that the optimal do main for the analog criteria should be concentrated in the tropical Indian Ocean region for IOD predictions. Including external forcing trends improves the skills of the east and west poles of the IOD, but not the IOD prediction itself. The MAF IOD prediction showed comparable skills to the assimilation-initialized hindcast, with skillful predictions corresponding to a 4- and 3-month lead respectively. The IOD forecast skills had significant decadal variations during the 55-year period, with low skills after the early 2000s and before 1985 and high skills during 1985–2000. This work offers a computational efficiency and practical approach for seasonal prediction of the tropical Indian Ocean sea surface temperature.
{"title":"Diagnosing seasonal forecast skill of the Indian Ocean Dipole mode using model-analogs","authors":"Yanling Wu, Youmin Tang","doi":"10.1175/jtech-d-22-0106.1","DOIUrl":"https://doi.org/10.1175/jtech-d-22-0106.1","url":null,"abstract":"\u0000A retrospective tropical Indian Ocean Dipole mode (IOD) hindcast for 1958–2014 was conducted using 20 models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), with a model-based analog forecast (MAF) method. In the MAF approach, forecast ensembles are extracted from preexisting model simulations by finding the states that initially best match an observed anomaly and tracking their subsequent evolution, with no additional model integrations. By optimizing the key factors in the MAF method, we suggest that the optimal do main for the analog criteria should be concentrated in the tropical Indian Ocean region for IOD predictions. Including external forcing trends improves the skills of the east and west poles of the IOD, but not the IOD prediction itself. The MAF IOD prediction showed comparable skills to the assimilation-initialized hindcast, with skillful predictions corresponding to a 4- and 3-month lead respectively. The IOD forecast skills had significant decadal variations during the 55-year period, with low skills after the early 2000s and before 1985 and high skills during 1985–2000. This work offers a computational efficiency and practical approach for seasonal prediction of the tropical Indian Ocean sea surface temperature.","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46987576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-12DOI: 10.1175/jtech-d-22-0093.1
P. Chamberlain, L. Talley, B. Cornuelle, M. Mazloff, S. Gille
The core Argo array has operated with the design goal of uniform spatial distribution of 3° in latitude and longitude. Recent studies have acknowledged that spatial and temporal scales of variability in some parts of the ocean are not resolved by 3° sampling and have recommended increased core Argo density in the equatorial region, boundary currents, and marginal seas with an integrated vision of other Argo variants. Biogeochemical (BGC) Argo floats currently observe the ocean from a collection of pilot arrays, but recently funded proposals will transition these pilot arrays to a global array. The current BGC Argo implementation plan recommends uniform spatial distribution of BGC Argo floats. For the first time, we estimate the effectiveness of the existing BGC Argo array to resolve the anomaly from the mean using a subset of modeled, full-depth BGC fields. We also study the effectiveness of uniformly-distributed BGC Argo arrays with varying float densities at observing the ocean. Then, using previous Argo trajectories, we estimate the Argo array’s future distribution and quantify how well it observes the ocean. Finally, using a novel technique for sequentially identifying the best deployment locations, we suggest the optimal array distribution for BGC Argo floats to minimize objective mapping uncertainty in a subset of BGC fields and to best constrain BGC temporal variability.
{"title":"Optimizing The Biogeochemical Argo Float Distribution","authors":"P. Chamberlain, L. Talley, B. Cornuelle, M. Mazloff, S. Gille","doi":"10.1175/jtech-d-22-0093.1","DOIUrl":"https://doi.org/10.1175/jtech-d-22-0093.1","url":null,"abstract":"\u0000The core Argo array has operated with the design goal of uniform spatial distribution of 3° in latitude and longitude. Recent studies have acknowledged that spatial and temporal scales of variability in some parts of the ocean are not resolved by 3° sampling and have recommended increased core Argo density in the equatorial region, boundary currents, and marginal seas with an integrated vision of other Argo variants. Biogeochemical (BGC) Argo floats currently observe the ocean from a collection of pilot arrays, but recently funded proposals will transition these pilot arrays to a global array. The current BGC Argo implementation plan recommends uniform spatial distribution of BGC Argo floats. For the first time, we estimate the effectiveness of the existing BGC Argo array to resolve the anomaly from the mean using a subset of modeled, full-depth BGC fields. We also study the effectiveness of uniformly-distributed BGC Argo arrays with varying float densities at observing the ocean. Then, using previous Argo trajectories, we estimate the Argo array’s future distribution and quantify how well it observes the ocean. Finally, using a novel technique for sequentially identifying the best deployment locations, we suggest the optimal array distribution for BGC Argo floats to minimize objective mapping uncertainty in a subset of BGC fields and to best constrain BGC temporal variability.","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42856665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-11DOI: 10.1175/jtech-d-23-0030.1
K. Smalley, M. Lebsock
Geostationary observations provide measurements of the cloud liquid water path (LWP), permitting continuous observation of cloud evolution throughout the daylit portion of the diurnal cycle. Relative to LWP derived from microwave imagery, these observations have biases related to scattering geometry, which systematically varies throughout the day. Therefore, we have developed a set of bias corrections using microwave LWP for the Geostationary Operational Environmental Satellites (GOES-16 and GOES-17) observations of LWP derived from retrieved cloud-optical properties. The bias corrections are defined based on scattering geometry (solar zenith, sensor zenith, and relative azimuth) and low-cloud fraction. We demonstrate that over the low-cloud regions of the northeast and southeast Pacific, these bias corrections drastically improve the characteristics of the retrieved LWP, including its regional distribution, diurnal variation, and evolution along short-time-scale Lagrangian trajectories.
{"title":"Corrections for Geostationary Cloud Liquid Water Path Using Microwave Imagery","authors":"K. Smalley, M. Lebsock","doi":"10.1175/jtech-d-23-0030.1","DOIUrl":"https://doi.org/10.1175/jtech-d-23-0030.1","url":null,"abstract":"\u0000Geostationary observations provide measurements of the cloud liquid water path (LWP), permitting continuous observation of cloud evolution throughout the daylit portion of the diurnal cycle. Relative to LWP derived from microwave imagery, these observations have biases related to scattering geometry, which systematically varies throughout the day. Therefore, we have developed a set of bias corrections using microwave LWP for the Geostationary Operational Environmental Satellites (GOES-16 and GOES-17) observations of LWP derived from retrieved cloud-optical properties. The bias corrections are defined based on scattering geometry (solar zenith, sensor zenith, and relative azimuth) and low-cloud fraction. We demonstrate that over the low-cloud regions of the northeast and southeast Pacific, these bias corrections drastically improve the characteristics of the retrieved LWP, including its regional distribution, diurnal variation, and evolution along short-time-scale Lagrangian trajectories.","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49437836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-07DOI: 10.1175/jtech-d-22-0132.1
F. Geyer, G. Gopalakrishnan, H. Sagen, B. Cornuelle, F. Challet, M. Mazloff
The 2010-2012 Acoustic Technology for Observing the Interior of the Arctic Ocean (ACOBAR) experiment provided acoustic tomography data along three 167-301 km long sections in Fram Strait between Greenland and Spitsbergen. Ocean sound speed data were assimilated into a regional numerical ocean model using the Massachusetts Institute of Technology General Circulation Model-Estimating the Circulation and Climate of the Ocean four-dimensional variational (MITgcm-ECCO 4DVAR) assimilation system. The resulting state estimate matched the assimilated sound speed time series, the root mean squared (RMS) error of the sound speed estimate (~0.4 m s−1) is smaller than the uncertainty of the measurement (~0.8 m s−1). Data assimilation improved modeled range-and-depth-averaged ocean temperatures at the 78°50’N oceanographic mooring section in Fram Strait. The RMS error of the state estimate (0.21°C) is comparable to the uncertainty of the interpolated mooring section (0.23°C). Lack of depth information in the assimilated ocean sound speed measurements caused an increased temperature bias in the upper ocean (0-500 m). The correlations with the mooring section were not improved as short-term variations in the mooring measurements and the ocean state estimate do not always coincide in time. This is likely due to the small-scale eddying and non-linearity of the ocean circulation in Fram Strait. Furthermore, the horizontal resolution of the state estimate (4.5 km) is eddy-permitting, rather than eddy resolving. Thus, the state estimate cannot represent the full ocean dynamics of the region. This study is the first to demonstrate the usefulness of large-scale acoustic measurements for improving ocean state estimates at high latitudes.
2010-2012年北冰洋内部观测声学技术(ACOBAR)实验提供了格陵兰岛和斯匹次卑尔根岛之间的弗拉姆海峡三个167-301公里长的剖面的声学层析成像数据。利用麻省理工学院环流模式-估算海洋环流和气候四维变分(MITgcm-ECCO 4DVAR)同化系统，将海洋声速数据同化为区域数值海洋模式。所得状态估计与同化的声速时间序列相匹配，声速估计的均方根误差(~0.4 m s−1)小于测量的不确定度(~0.8 m s−1)。数据同化改善了Fram海峡78°50′n海洋系泊段的距离和深度平均海洋温度模型。状态估计的均方根误差(0.21°C)与内插系泊段的不确定性(0.23°C)相当。在同化的海洋声速测量中缺乏深度信息导致上层海洋(0-500 m)的温度偏差增加。由于系泊测量的短期变化和海洋状态估计并不总是在时间上一致，因此与系泊段的相关性没有得到改善。这可能是由于弗拉姆海峡的小尺度涡旋和海洋环流的非线性。此外，状态估计(4.5 km)的水平分辨率是允许涡流的，而不是涡流分辨率。因此，状态估计不能代表该地区的全部海洋动态。这项研究首次证明了大规模声学测量对改善高纬度地区海洋状态估计的有用性。
{"title":"Data assimilation of range-and-depth-averaged sound speed from acoustic tomography measurements in Fram Strait","authors":"F. Geyer, G. Gopalakrishnan, H. Sagen, B. Cornuelle, F. Challet, M. Mazloff","doi":"10.1175/jtech-d-22-0132.1","DOIUrl":"https://doi.org/10.1175/jtech-d-22-0132.1","url":null,"abstract":"\u0000The 2010-2012 Acoustic Technology for Observing the Interior of the Arctic Ocean (ACOBAR) experiment provided acoustic tomography data along three 167-301 km long sections in Fram Strait between Greenland and Spitsbergen. Ocean sound speed data were assimilated into a regional numerical ocean model using the Massachusetts Institute of Technology General Circulation Model-Estimating the Circulation and Climate of the Ocean four-dimensional variational (MITgcm-ECCO 4DVAR) assimilation system. The resulting state estimate matched the assimilated sound speed time series, the root mean squared (RMS) error of the sound speed estimate (~0.4 m s−1) is smaller than the uncertainty of the measurement (~0.8 m s−1). Data assimilation improved modeled range-and-depth-averaged ocean temperatures at the 78°50’N oceanographic mooring section in Fram Strait. The RMS error of the state estimate (0.21°C) is comparable to the uncertainty of the interpolated mooring section (0.23°C). Lack of depth information in the assimilated ocean sound speed measurements caused an increased temperature bias in the upper ocean (0-500 m). The correlations with the mooring section were not improved as short-term variations in the mooring measurements and the ocean state estimate do not always coincide in time. This is likely due to the small-scale eddying and non-linearity of the ocean circulation in Fram Strait. Furthermore, the horizontal resolution of the state estimate (4.5 km) is eddy-permitting, rather than eddy resolving. Thus, the state estimate cannot represent the full ocean dynamics of the region. This study is the first to demonstrate the usefulness of large-scale acoustic measurements for improving ocean state estimates at high latitudes.","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47874836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-01DOI: 10.1175/jtech-d-22-0048.1
S. Durden, R. Beauchamp, S. Graniello, V. Venkatesh, S. Tanelli
The displaced phased center antenna (DPCA) method of clutter cancellation for ground moving target detection from airborne platforms has been in use for a number of decades. Application of the DPCA method for spaceborne Doppler weather radar velocity estimation was suggested in 2007. The initial description and analysis of the technique was followed several years ago by demonstration using a multiantenna airborne radar. Recent reviews of methods and technology for spaceborne cloud and precipitation radar have also mentioned possible use of DPCA. However, to date, analyses of the application of DPCA to spaceborne Doppler weather radar have assumed that the two channels and antennas are identical, including perfect alignment, and that the DPCA condition is well-satisfied. This study uses simulation to examine the effects of relaxing these assumptions. The simulation method and its validation are discussed, with companion analytical calculations in the appendix. Next, simulations are used to show the effects on the Doppler estimates from errors in pointing and positioning relative to the ideal DPCA. The DPCA technique is relatively robust to possible errors, indicating that a practical DPCA radar system can provide precise Doppler measurements from space. Analytical and simulation results show that the displaced phase center antenna approach can enable spaceborne atmospheric Doppler radar measurements with good accuracy, even in the presence of antenna mispointing and other system errors.
{"title":"DPCA-Based Doppler Radar Measurements from Space: Effect of System Errors on Velocity Estimation Performance","authors":"S. Durden, R. Beauchamp, S. Graniello, V. Venkatesh, S. Tanelli","doi":"10.1175/jtech-d-22-0048.1","DOIUrl":"https://doi.org/10.1175/jtech-d-22-0048.1","url":null,"abstract":"\u0000The displaced phased center antenna (DPCA) method of clutter cancellation for ground moving target detection from airborne platforms has been in use for a number of decades. Application of the DPCA method for spaceborne Doppler weather radar velocity estimation was suggested in 2007. The initial description and analysis of the technique was followed several years ago by demonstration using a multiantenna airborne radar. Recent reviews of methods and technology for spaceborne cloud and precipitation radar have also mentioned possible use of DPCA. However, to date, analyses of the application of DPCA to spaceborne Doppler weather radar have assumed that the two channels and antennas are identical, including perfect alignment, and that the DPCA condition is well-satisfied. This study uses simulation to examine the effects of relaxing these assumptions. The simulation method and its validation are discussed, with companion analytical calculations in the appendix. Next, simulations are used to show the effects on the Doppler estimates from errors in pointing and positioning relative to the ideal DPCA. The DPCA technique is relatively robust to possible errors, indicating that a practical DPCA radar system can provide precise Doppler measurements from space.\u0000\u0000\u0000Analytical and simulation results show that the displaced phase center antenna approach can enable spaceborne atmospheric Doppler radar measurements with good accuracy, even in the presence of antenna mispointing and other system errors.\u0000","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46894986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-29DOI: 10.1175/jtech-d-22-0078.1
Zhong‐Kuo Zhao, E. D’Asaro
Rain in tropical cyclones is studied using eight time series of underwater ambient sound at 40 Hz–50 kHz with wind speeds up to 45ms−1 beneath three tropical cyclones. At tropical cyclone wind speeds, rain- and wind-generated sound levels are comparable, so that rain cannot be detected by sound level alone. A rain detection algorithm based on the variations of 5–30 kHz sound levels with periods longer than 20 seconds and shorter than 30 minutes is proposed. Faster fluctuations (<20 s) are primarily due to wave breaking, and slower ones (>30 min) due to overall wind variations. Higher frequency sound (>30 kHz) is strongly attenuated by bubble clouds. This approach is supported by observations that, for wind speeds <40 m s−1, the variation in sound level is much larger than that expected from observed wind variations, and roughly comparable with that expected from rain variations. The hydrophone results are consistent with rain estimates by the Tropical Rainfall Measuring Mission (TRMM) satellite and with Stepped-Frequency Microwave Radiometer (SFMR) and radar estimates by surveillance flights. The observations indicate that the rain-generated sound fluctuations have broadband acoustic spectra centered around 10 kHz. Acoustically detected rain events usually last for a few minutes. The data used in this study are insufficient to produce useful estimation of rain rate from ambient sound, due to limited quantity and accuracy of the validation data. The frequency dependence of sound variations suggests that quantitative rainfall algorithms from ambient sound may be developed using multiple sound frequencies.
在三个热带气旋下，使用8个40 Hz-50 kHz的水下环境声时间序列，风速高达45ms−1，研究了热带气旋中的降雨。在热带气旋风速下，降雨和风产生的声级是相当的，因此不能仅通过声级来探测降雨。提出了一种基于周期大于20秒小于30分钟的5 ~ 30 kHz声级变化的降雨检测算法。由于整体风向变化，波动更快(30分钟)。更高频率的声音(bb0 - 30khz)被气泡云强烈衰减。对于风速<40 m s - 1的观测结果，声级的变化远远大于观测到的风变化的预期值，与降雨变化的预期值大致相当。水听器的结果与热带降雨测量任务(TRMM)卫星的降雨估计、步进频率微波辐射计(SFMR)和监视飞行的雷达估计相一致。观测结果表明，雨声波动具有以10khz为中心的宽带声谱。声波探测到的降雨事件通常持续几分钟。由于验证数据的数量和准确性有限，本研究中使用的数据不足以从环境声中产生有用的降雨率估计。声音变化的频率依赖性表明，可以使用多个声音频率开发来自环境声音的定量降雨算法。
{"title":"Detection of rain in tropical cyclones by underwater ambient sound","authors":"Zhong‐Kuo Zhao, E. D’Asaro","doi":"10.1175/jtech-d-22-0078.1","DOIUrl":"https://doi.org/10.1175/jtech-d-22-0078.1","url":null,"abstract":"\u0000Rain in tropical cyclones is studied using eight time series of underwater ambient sound at 40 Hz–50 kHz with wind speeds up to 45ms−1 beneath three tropical cyclones. At tropical cyclone wind speeds, rain- and wind-generated sound levels are comparable, so that rain cannot be detected by sound level alone. A rain detection algorithm based on the variations of 5–30 kHz sound levels with periods longer than 20 seconds and shorter than 30 minutes is proposed. Faster fluctuations (<20 s) are primarily due to wave breaking, and slower ones (>30 min) due to overall wind variations. Higher frequency sound (>30 kHz) is strongly attenuated by bubble clouds. This approach is supported by observations that, for wind speeds <40 m s−1, the variation in sound level is much larger than that expected from observed wind variations, and roughly comparable with that expected from rain variations. The hydrophone results are consistent with rain estimates by the Tropical Rainfall Measuring Mission (TRMM) satellite and with Stepped-Frequency Microwave Radiometer (SFMR) and radar estimates by surveillance flights. The observations indicate that the rain-generated sound fluctuations have broadband acoustic spectra centered around 10 kHz. Acoustically detected rain events usually last for a few minutes. The data used in this study are insufficient to produce useful estimation of rain rate from ambient sound, due to limited quantity and accuracy of the validation data. The frequency dependence of sound variations suggests that quantitative rainfall algorithms from ambient sound may be developed using multiple sound frequencies.","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41514512","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-12DOI: 10.1175/jtech-d-22-0070.1
P. Chamberlain, L. Talley, M. Mazloff, E. van Sebille, S. Gille, T. tucker, M. Scanderbeg, Pelle E. Robbins
The Argo array provides nearly 4000 temperature and salinity profiles of the top 2000 meters of the ocean every 10 days. Still, Argo floats will never be able to measure the ocean at all times, everywhere. Optimized Argo float distributions should match the spatial and temporal variability of the many societally important ocean features that they observe. Determining these distributions is challenging because float advection is difficult to predict. Using no external models, transition matrices based on existing Argo trajectories provide statistical inferences about Argo float motion. We use the 24 years of Argo locations to construct an optimal transition matrix that minimizes estimation bias and uncertainty. The optimal array is determined to have a 2°×2° spatial resolution with a 90 day timestep. We then use the transition matrix to predict the probability of future float locations of the Core Argo array, the Global Biogeochemical Array, and the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) array. A comparison of transition matrices derived from floats using Argos System and Iridium communication methods shows the impact of surface displacements, which is most apparent near the equator. Additionally, we demonstrate the utility of transition matrices for validating models by comparing the matrix derived from Argo floats with that derived from a particle release experiment in the Southern Ocean State Estimate (SOSE).
{"title":"Using existing Argo trajectories to statistically predict future float positions with a transition matrix","authors":"P. Chamberlain, L. Talley, M. Mazloff, E. van Sebille, S. Gille, T. tucker, M. Scanderbeg, Pelle E. Robbins","doi":"10.1175/jtech-d-22-0070.1","DOIUrl":"https://doi.org/10.1175/jtech-d-22-0070.1","url":null,"abstract":"\u0000The Argo array provides nearly 4000 temperature and salinity profiles of the top 2000 meters of the ocean every 10 days. Still, Argo floats will never be able to measure the ocean at all times, everywhere. Optimized Argo float distributions should match the spatial and temporal variability of the many societally important ocean features that they observe. Determining these distributions is challenging because float advection is difficult to predict. Using no external models, transition matrices based on existing Argo trajectories provide statistical inferences about Argo float motion. We use the 24 years of Argo locations to construct an optimal transition matrix that minimizes estimation bias and uncertainty. The optimal array is determined to have a 2°×2° spatial resolution with a 90 day timestep. We then use the transition matrix to predict the probability of future float locations of the Core Argo array, the Global Biogeochemical Array, and the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) array. A comparison of transition matrices derived from floats using Argos System and Iridium communication methods shows the impact of surface displacements, which is most apparent near the equator. Additionally, we demonstrate the utility of transition matrices for validating models by comparing the matrix derived from Argo floats with that derived from a particle release experiment in the Southern Ocean State Estimate (SOSE).","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42785393","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-06-07DOI: 10.1175/jtech-d-22-0088.1
N. Privé, M. McLinden, B. Lin, I. Moradi, M. Sienkiewicz, G. Heymsfield, W. McCarty
A new instrument has been proposed for measuring surface air pressure over the marine surface with a combined active/passive scanning multi-channel differential absorption radar (DAR) to provide an estimate of the total atmospheric column oxygen content. A demonstrator instrument, the Microwave Barometric Radar and Sounder (MBARS), has been funded by the National Aeronautics and Space Administration (NASA) for airborne test missions. Here, a proof-of-concept study to evaluate the potential impact of spaceborne surface pressure data on numerical weather prediction is performed using the Goddard Modeling and Assimilation Office global observing system simulation experiment (OSSE) framework. This OSSE framework employs the Goddard Earth Observing System model and the hybrid 4D ensemble variational Gridpoint Statistical Interpolation data assimilation system. Multiple flight and scanning configurations of potential spaceborne orbits are examined. Swath width and observation spacing for the surface pressure data are varied to explore a range of sampling strategies. For wider swaths, the addition of surface pressures reduces the root mean square surface pressure analysis error by as much as 20% over some ocean regions. The forecast sensitivity observation impact tool estimates impacts on the Pacific Ocean basin boundary layer 24-hour forecast temperatures for spaceborne surface pressures on par with rawinsondes and aircraft, and greater impacts than the current network of ships and buoys. The largest forecast impacts are found in the southern hemisphere extratropics.
{"title":"Impacts of marine surface pressure observations from a spaceborne differential absorption radar investigated with an observing system simulation experiment","authors":"N. Privé, M. McLinden, B. Lin, I. Moradi, M. Sienkiewicz, G. Heymsfield, W. McCarty","doi":"10.1175/jtech-d-22-0088.1","DOIUrl":"https://doi.org/10.1175/jtech-d-22-0088.1","url":null,"abstract":"\u0000A new instrument has been proposed for measuring surface air pressure over the marine surface with a combined active/passive scanning multi-channel differential absorption radar (DAR) to provide an estimate of the total atmospheric column oxygen content. A demonstrator instrument, the Microwave Barometric Radar and Sounder (MBARS), has been funded by the National Aeronautics and Space Administration (NASA) for airborne test missions. Here, a proof-of-concept study to evaluate the potential impact of spaceborne surface pressure data on numerical weather prediction is performed using the Goddard Modeling and Assimilation Office global observing system simulation experiment (OSSE) framework. This OSSE framework employs the Goddard Earth Observing System model and the hybrid 4D ensemble variational Gridpoint Statistical Interpolation data assimilation system.\u0000Multiple flight and scanning configurations of potential spaceborne orbits are examined. Swath width and observation spacing for the surface pressure data are varied to explore a range of sampling strategies. For wider swaths, the addition of surface pressures reduces the root mean square surface pressure analysis error by as much as 20% over some ocean regions. The forecast sensitivity observation impact tool estimates impacts on the Pacific Ocean basin boundary layer 24-hour forecast temperatures for spaceborne surface pressures on par with rawinsondes and aircraft, and greater impacts than the current network of ships and buoys. The largest forecast impacts are found in the southern hemisphere extratropics.","PeriodicalId":15074,"journal":{"name":"Journal of Atmospheric and Oceanic Technology","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41691415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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