Modulation loops, time lag and relationship between cosmic ray intensity and tilt of the heliospheric current sheet

Aims.We study certain aspects of the solar modulation of galactic cosmic ray intensity during different solar activity cycles and in different polarity states of the heliosphere. Methods.We plotted modulation loops between the cosmic ray intensity and the tilt angle of the heliospheric current sheet during three solar activity cycles 21, 22 and 23 and obtained the area of modulation loops. The time lag between the tilt angle and the cosmic ray intensity in odd, even solar activity cycles and during $A >$ 0, $A <$ 0 polarity states of the heliosphere are determined using correlation analysis. Rate of intensity decrease with tilt angle during different solar and magnetic cycles are estimated from best fit method. Results.Marked differences during the two odd and the one even solar cycles, as well as during different polarity states of the solar magnetic field ($A >$ 0 and $A$ 0 and $A$ 0, indicating stronger response to the tilt angle changes during $A <$ 0. These results are discussed in the light of 3D modulation models including the gradient and curvature drifts and the tilt of the heliospheric current sheet

Characteristic features of ICMEs associated with big storms in geomagnetic activity and large Forbush decreases in cosmic ray intensity

265-269The solar sources and features of interplanetary structures associated with big geomagnetic storm (GS) and/or large Forbush decrease (FD) events have been investigated. The hourly data of geomagnetic activity, cosmic ray (CR) intensity, and solar wind plasma/field has been utilized during the passage of ICMEs and associated structures (e.g. shock/seath, interaction region/high speed stream). The geo-effectiveness and CR-effectiveness of ICMEs, similarities and distinctions between them together with variations/fluctuations in interplanetary plasma/field parameters is utilized in order to identify distinct feature(s) of ICMEs and physical mechanism(s) playing important role in the development of GS and FD

Global Impact of COVID-19 on Stroke Care and IV Thrombolysis

OBJECTIVE: To measure the global impact of COVID-19 pandemic on volumes of IV thrombolysis (IVT), IVT transfers, and stroke hospitalizations over 4 months at the height of the pandemic (March 1 to June 30, 2020) compared with 2 control 4-month periods. METHODS: We conducted a cross-sectional, observational, retrospective study across 6 continents, 70 countries, and 457 stroke centers. Diagnoses were identified by their ICD-10 codes or classifications in stroke databases. RESULTS: There were 91,373 stroke admissions in the 4 months immediately before compared to 80,894 admissions during the pandemic months, representing an 11.5% (95% confidence interval [CI] -11.7 to -11.3, p &lt; 0.0001) decline. There were 13,334 IVT therapies in the 4 months preceding compared to 11,570 procedures during the pandemic, representing a 13.2% (95% CI -13.8 to -12.7, p &lt; 0.0001) drop. Interfacility IVT transfers decreased from 1,337 to 1,178, or an 11.9% decrease (95% CI -13.7 to -10.3, p = 0.001). Recovery of stroke hospitalization volume (9.5%, 95% CI 9.2-9.8, p &lt; 0.0001) was noted over the 2 later (May, June) vs the 2 earlier (March, April) pandemic months. There was a 1.48% stroke rate across 119,967 COVID-19 hospitalizations. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was noted in 3.3% (1,722/52,026) of all stroke admissions. CONCLUSIONS: The COVID-19 pandemic was associated with a global decline in the volume of stroke hospitalizations, IVT, and interfacility IVT transfers. Primary stroke centers and centers with higher COVID-19 inpatient volumes experienced steeper declines. Recovery of stroke hospitalization was noted in the later pandemic months. © 2021 American Academy of Neurology