Localized fast flow disturbance observed in the plasma sheet and in the ionosphere

Abstract. An isolated plasma sheet flow burst took place at 22:02 UT, 1 September 2002, when the Cluster footpoint was located within the area covered by the Magnetometers-Ionospheric Radars-All-sky Cameras Large Experiment (MIRACLE). The event was associated with a clear but weak ionospheric disturbance and took place during a steady southward IMF interval, about 1h preceding a major substorm onset. Multipoint observations, both in space and from the ground, allow us to discuss the temporal and spatial scale of the disturbance both in the magnetosphere and ionosphere. Based on measurements from four Cluster spacecraft it is inferred that Cluster observed the dusk side part of a localized flow channel in the plasma sheet with a flow shear at the front, suggesting a field-aligned current out from the ionosphere. In the ionosphere the equivalent current pattern and possible field-aligned current location show a pattern similar to the auroral streamers previously obtained during an active period, except for its spatial scale and amplitude. It is inferred that the footpoint of Cluster was located in the region of an upward field-aligned current, consistent with the magnetospheric observations. The entire disturbance in the ionosphere lasted about 10min, consistent with the time scale of the current sheet disturbance in the magnetosphere. The plasma sheet bulk flow, on the other hand, had a time scale of about 2min, corresponding to the time scale of an equatorward excursion of the enhanced electrojet. These observations confirm that localized enhanced convection in the magnetosphere and associated changes in the current sheet structure produce a signature with consistent temporal and spatial scale at the conjugate ionosphere.

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Dynamics at the demographic time scale

Mathematical Tools for Understanding Infectious Disease Dynamics ◽

10.23943/princeton/9780691155395.003.0004 ◽

2012 ◽

Author(s):

Odo Diekmann ◽

Hans Heesterbeek ◽

Tom Britton

Keyword(s):

Population Growth ◽

Spatial Scale ◽

Time Scale ◽

Host Population ◽

Temporal And Spatial ◽

Two Parameters ◽

Infective Agent

This chapter focuses on the influence of the demography on the persistence of an infective agent, and vice versa on the influence of the agent on host population growth and persistence. When new “fuel” is provided through the replacement of immune individuals by newborn susceptibles, the infective agent may strike again at a later time or even persist and become endemic. Whether we observe repeated outbreaks or relatively small fluctuations around a steady endemic level depends on the temporal and spatial scale that we, as investigators of the system, choose to monitor and/or to model. The chapter also suggests that two parameters, rather than just one, are needed to distinguish between a single outbreak (which may reoccur much later by reintroduction of the agent from the outside) and the endemic situation.

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8-Day and Daily Maximum and Minimum Air Temperature Estimation via Machine Learning Method on a Climate Zone to Global Scale

Remote Sensing ◽

10.3390/rs13122355 ◽

2021 ◽

Vol 13 (12) ◽

pp. 2355

Author(s):

Linglin Zeng ◽

Yuchao Hu ◽

Rui Wang ◽

Xiang Zhang ◽

Guozhang Peng ◽

...

Keyword(s):

Spatial Scale ◽

Air Temperature ◽

Spatial Scales ◽

Model Performance ◽

Global Scale ◽

Scale Model ◽

Validation Dataset ◽

Daily Maximum ◽

Climate Zone ◽

Temporal And Spatial

Air temperature (Ta) is a required input in a wide range of applications, e.g., agriculture. Land Surface Temperature (LST) products from Moderate Resolution Imaging Spectroradiometer (MODIS) are widely used to estimate Ta. Previous studies of these products in Ta estimation, however, were generally applied in small areas and with a small number of meteorological stations. This study designed both temporal and spatial experiments to estimate 8-day and daily maximum and minimum Ta (Tmax and Tmin) on three spatial scales: climate zone, continental and global scales from 2009 to 2018, using the Random Forest (RF) method based on MODIS LST products and other auxiliary data. Factors contributing to the relation between LST and Ta were determined based on physical models and equations. Temporal and spatial experiments were defined by the rules of dividing the training and validation datasets for the RF method, in which the stations selected in the training dataset were all included or not in the validation dataset. The RF model was first trained and validated on each spatial scale, respectively. On a global scale, model accuracy with a determination coefficient (R2) > 0.96 and root mean square error (RMSE) < 1.96 °C and R2 > 0.95 and RMSE < 2.55 °C was achieved for 8-day and daily Ta estimations, respectively, in both temporal and spatial experiments. Then the model was trained and cross-validated on each spatial scale. The results showed that the data size and station distribution of the study area were the main factors influencing the model performance at different spatial scales. Finally, the spatial patterns of the model performance and variable importance were analyzed. Both daytime and nighttime LST had a significant contribution in the 8-day Tmax estimation on all the three spatial scales; while their contribution in daily Tmax estimation varied over different continents or climate zones. This study was expected to improve our understanding of Ta estimation in terms of accuracy variations and influencing variables on different spatial and temporal scales. The future work mainly includes identifying underlying mechanisms of estimation errors and the uncertainty sources of Ta estimation from a local to a global scale.

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Electromagnetic ELF wave intensification associated with fast earthward flows in mid-tail plasma sheet

Annales Geophysicae ◽

10.5194/angeo-30-467-2012 ◽

2012 ◽

Vol 30 (3) ◽

pp. 467-488 ◽

Cited By ~ 7

Author(s):

J. Liang ◽

B. Ni ◽

C. M. Cully ◽

E. F. Donovan ◽

R. M. Thorne ◽

...

Keyword(s):

Plasma Sheet ◽

Occurrence Rate ◽

Lower Hybrid ◽

Angle Distribution ◽

Frequency Range ◽

Frequency Wave ◽

Whistler Mode ◽

Central Plasma ◽

Fast Flow ◽

Flow Activity

Abstract. In this study we perform a statistical survey of the extremely-low-frequency wave activities associated with fast earthward flows in the mid-tail central plasma sheet (CPS) based upon THEMIS measurements. We reveal clear trends of increasing wave intensity with flow enhancement over a broad frequency range, from below fLH (lower-hybrid resonant frequency) to above fce (electron gyrofrequency). We mainly investigate two electromagnetic wave modes, the lower-hybrid waves at frequencies below fLH, and the whistler-mode waves in the frequency range fLH < f < fce. The waves at f < fLH dramatically intensify during fast flow intervals, and tend to contain strong electromagnetic components in the high-plasma-beta CPS region, consistent with the theoretical expectation of the lower-hybrid drift instability in the center region of the tail current sheet. ULF waves with very large perpendicular wavenumber might be Doppler-shifted by the flows and also partly contribute to the observed waves in the lower-hybrid frequency range. The fast flow activity substantially increases the occurrence rate and peak magnitude of the electromagnetic waves in the frequency range fLH < f < fce, though they still tend to be short-lived and sporadic in occurrence. We also find that the electron pitch-angle distribution in the mid-tail CPS undergoes a variation from negative anisotropy (perpendicular temperature smaller than parallel temperature) during weak flow intervals, to more or less positive anisotropy (perpendicular temperature larger than parallel temperature) during fast flow intervals. The flow-related electromagnetic whistler-mode wave tends to occur in conjunction with positive electron anisotropy.

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Characteristics of Climate Change and Extreme Weather from 1951 to 2011 in China

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph15112540 ◽

2018 ◽

Vol 15 (11) ◽

pp. 2540 ◽

Cited By ~ 4

Author(s):

Chunli Zhao ◽

Jianguo Chen ◽

Peng Du ◽

Hongyong Yuan

Keyword(s):

Climate Change ◽

Spatial Scale ◽

Spatial Scales ◽

Seasonal Fluctuation ◽

Extreme Weather ◽

Temperature And Precipitation ◽

Weather Variation ◽

Variation Characteristics ◽

Established Fact ◽

Temporal And Spatial

It has been demonstrated that climate change is an established fact. A good comprehension of climate and extreme weather variation characteristics on a temporal and a spatial scale is important for adaptation and response. In this work, the characteristics of temperature, precipitation, and extreme weather distribution and variation is summarized for a period of 60 years and the seasonal fluctuation of temperature and precipitation is also analyzed. The results illustrate the reduction in daily and annual temperature divergence on both temporal and spatial scales. However, the gaps remain relatively significant. Furthermore, the disparity in daily and annual precipitation are found to be increasing on both temporal and spatial scales. The findings indicate that climate change, to a certain extent, narrowed the temperature gap while widening the precipitation gap on temporal and spatial scales in China.

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