scholarly journals Comparison of Seasonal foEs and fbEs Occurrence Rates Derived from Global Digisonde Measurements

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1558
Author(s):  
Dawn K. Merriman ◽  
Omar A. Nava ◽  
Eugene V. Dao ◽  
Daniel J. Emmons
Keyword(s):  
Southern Hemisphere ◽  
Lower Limit ◽  
Northern Hemisphere ◽  
Radio Occultation ◽  
Austral Summer ◽  
Peak Frequency ◽  
Boreal Summer ◽  
Gps Radio Occultation ◽  
Drastic Decrease ◽  
Sporadic E

A global climatology of sporadic-E occurrence rates (ORs) based on ionosonde measurements is presented for the peak blanketing frequency, fbEs, and the ordinary mode peak frequency of the layer, foEs. ORs are calculated for a variety of sporadic-E frequency thresholds: no lower limit, 3, 5, and 7 MHz. Seasonal rates are calculated from 64 Digisonde sites during the period 2006–2020 using ionograms either manually or automatically scaled with ARTIST-5. Both foEs and fbEs ORs peak in the Northern Hemisphere during the boreal summer, with a decrease by roughly a factor of 2–3 in fbEs rates relative to foEs rates without a lower threshold on the sporadic-E intensity. This ratio of foEs to fbEs OR increases with increasing sporadic-E intensity, up to a factor of 5 for the 7 MHz threshold. An asymmetry is observed with the Southern Hemisphere peaks during the austral summer, with slightly lower rates compared with the Northern Hemisphere during the boreal summer. A drastic decrease in ORs is observed for the higher intensity thresholds, such that the fbEs occurrence rates for 7 MHz are nearly zero during most locations and seasons. These updated occurrence rates can be used for future statistical comparisons with GPS radio occultation-based sporadic-E occurrence rates.

scholarly journals A~characterization of thermal structure and conditions for overshooting of tropical and extratropical cyclones with GPS radio occultation

2014 ◽  
Vol 14 (21) ◽  
pp. 29395-29428 ◽  
Author(s):  
R. Biondi ◽  
A. K. Steiner ◽  
G. Kirchengast ◽  
T. Rieckh
Keyword(s):  
Tropical Cyclones ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Radio Occultation ◽  
Time Window ◽  
Mutual Influence ◽  
Temperature Anomaly ◽  
Thermal Structure ◽  
Ocean Basin ◽  
Gps Radio Occultation

Abstract. The thermal structure of Tropical Cyclones (TCs) in different ocean basins is studied using Global Positioning System (GPS) Radio Occultation (RO) measurements co-located with TCs' best tracks. The objective of this work is to understand the mutual influence of TCs and atmospheric parameters in different regions. We selected more than 20 000 GPS RO profiles co-located with TCs in a time window of 6 h and space window of 600 km from the TC center in the period 2001–2012 and classified them by intensity of the cyclone and by ocean basin. The results show that tropical cyclones have different characteristics depending on the basin, which affects the cloud top altitude, and the TC thermal structure, which usually shows a negative temperature anomaly near the cloud top altitude. In the Northern Hemisphere ocean basins, the temperature anomaly becomes positive above the cloud top, while in the Southern Hemisphere ocean basins, it stays negative up to about 25 km of altitude. Furthermore, in the Southern Hemisphere the storms reach higher cloud top altitudes than in the Northern Hemisphere ocean basins, indicating that possible overshootings overpass the climatological tropopause more deeply at extratropical latitudes. The comparison of the TC thermal structure with the respective monthly mean tropopause altitude allows a detailed analysis of the probability for possible overshooting. While the co-locations between GPS ROs and TC tracks are well distributed in all the ocean basins, conditions for possible overshootings are found to be more frequent in the Southern Hemisphere basins and in the North Indian ocean basin. However the number of possible overshootings for high intensities (i.e. TC categories 1–5) is highest in the West Pacific ocean basin.

scholarly journals Characterization of thermal structure and conditions for overshooting of tropical and extratropical cyclones with GPS radio occultation

2015 ◽  
Vol 15 (9) ◽  
pp. 5181-5193 ◽  
Author(s):  
R. Biondi ◽  
A. K. Steiner ◽  
G. Kirchengast ◽  
T. Rieckh
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Radio Occultation ◽  
Time Window ◽  
Mutual Influence ◽  
Temperature Anomaly ◽  
Thermal Structure ◽  
Negative Temperature ◽  
Ocean Basin ◽  
Gps Radio Occultation

Abstract. The thermal structure of tropical cyclones (TCs) in different ocean basins is studied using global positioning system (GPS) radio occultation (RO) measurements co-located with TCs' best tracks. The objective of this work is to understand the mutual influence of TCs and atmospheric parameters in different regions. We selected more than 20 000 GPS RO profiles co-located with TCs in a time window of 6 h and space window of 600 km from the TC center in the period 2001–2012 and classified them by intensity of the cyclone and by ocean basin. The results show that TCs have different characteristics depending on the basin, which affects the cloud top altitude and the TC thermal structure which usually shows a negative temperature anomaly near the cloud top altitude. In the Northern Hemisphere ocean basins, the temperature anomaly becomes positive above the cloud top while in the Southern Hemisphere ocean basins it stays negative up to about 25 km in altitude. Furthermore, in the Southern Hemisphere the storms reach higher cloud top altitudes than in the Northern Hemisphere ocean basins, indicating that possible overshootings overpass the climatological tropopause more deeply at extratropical latitudes. The comparison of the TC thermal structure with the respective monthly mean tropopause altitude allows for a detailed analysis of the probability for possible overshooting. While the co-locations between GPS ROs and TC tracks are well distributed in all the ocean basins, conditions for possible overshootings are found to be more frequent in the Southern Hemisphere basins and in the northern Indian Ocean basin. However, the number of possible overshootings for high intensity storms (i.e., TC categories 1–5) is the highest in the western Pacific Ocean basin.

scholarly journals Enhanced sporadic <i>E</i> occurrence rates during the Geminid meteor showers 2006–2010

2013 ◽  
Vol 11 ◽  
pp. 313-318 ◽  
Author(s):  
C. Jacobi ◽  
C. Arras ◽  
J. Wickert
Keyword(s):  
Northern Hemisphere ◽  
Strong Correlation ◽  
Wind Shear ◽  
Radio Occultation ◽  
Semidiurnal Tide ◽  
Metallic Ions ◽  
Meteor Radar ◽  
Meteor Showers ◽  
Short Delay ◽  
Sporadic E

Abstract. Northern Hemisphere midlatitude sporadic E (Es) layer occurrence rates derived from FORMOSAT-3/COSMIC GPS radio occultation (RO) measurements during the Geminid meteor showers 2006–2010 are compared with meteor rates obtained with the Collm (51.3° N, 13.0° E) VHF meteor radar. In most years, Es rates increase after the shower, with a short delay of few days. This indicates a possible link between meteor influx and the production of metallic ions that may form Es. There is an indication that the increase propagates downward, probably partly caused by tidal wind shear. However, the correlation between Es rates and meteor flux varies from year to year. A strong correlation is found especially in 2009, while in 2010 Es rates even decrease during the shower. This indicates that additional processes significantly influence Es occurrence also during meteor showers. A possible effect of the semidiurnal tide is found. During years with weaker tidal wind shear, the correlation between Es and meteor rates is even weaker.

scholarly journals Tidal wind shear observed by meteor radar and comparison with sporadic E occurrence rates based on GPS radio occultation observations

2019 ◽  
Vol 17 ◽  
pp. 213-224
Author(s):  
Christoph Jacobi ◽  
Christina Arras
Keyword(s):  
Wind Shear ◽  
Radio Occultation ◽  
Signal To Noise Ratio ◽  
Lower Thermosphere ◽  
Horizontal Component ◽  
Meteor Radar ◽  
Good Correspondence ◽  
Gps Radio Occultation ◽  
Middle Latitudes ◽  
Sporadic E

Abstract. We analyze tidal (diurnal, semidiurnal, terdiurnal, quarterdiurnal) phases and related wind shear in the mesosphere/lower thermosphere as observed by meteor radar over Collm (51.3∘ N, 13.0∘ E). The wind shear phases are compared with those of sporadic E (Es) occurrence rates, which were derived from GPS radio occultation signal-to-noise ratio (SNR) profiles measured by the COSMIC/FORMOSAT-3 satellites. At middle latitudes Es are mainly produced by wind shear, which, in the presence of a horizontal component of the Earth's magnetic field, leads to ion convergence in the region where the wind shear is negative. Consequently, we find good correspondence between radar derived wind shear and Es phases for the semidiurnal, terdiurnal, and quarterdiurnal tidal components. The diurnal tidal wind shear, however, does not correspond to the Es diurnal signal.

scholarly journals Weak Southern Hemispheric monsoons during the Last Interglacial period

2020 ◽  
Author(s):  
Nicholas K. H. Yeung ◽  
Laurie Menviel ◽  
Katrin J. Meissner ◽  
Andréa S. Taschetto ◽  
Tilo Ziehn ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Austral Summer ◽  
Hadley Cell ◽  
Boreal Summer ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Inter Tropical Convergence Zone ◽  
High Northern Latitude ◽  
Summer Insolation ◽  
Last Interglacial Period

Abstract. Due to different orbital configurations, high northern latitude boreal summer insolation was higher during the Last Interglacial period (LIG; 129–116 thousand years before present, ka) than during the preindustrial period (PI), while high southern latitude austral summer insolation was lower. The climatic response to these changes is studied here with focus on the southern hemispheric monsoons, by performing an equilibrium experiment of the LIG at 127 ka with the Australian Earth System Model, ACCESS-ESM1.5, as part of the Paleoclimate Model Intercomparison Project 4 (PMIP4). In our simulation, mean surface air temperature increases by 6.5 °C over land during boreal summer between 40° N and 60° N in the LIG compared to PI, leading to a northward shift of the Inter-Tropical Convergence Zone (ITCZ) and a strengthening of the North African and Indian monsoons. Despite 0.4 °C cooler conditions in austral summer in the Southern Hemisphere (0–90° S), annual mean air temperatures are 1.2 °C higher at southern mid-to-high latitudes (40° S–80° S). These differences in temperature are coincident with a large-scale reorganisation of the atmospheric circulation. The ITCZ shifts southward in the Atlantic and Indian sectors during the LIG austral summer compared to PI, leading to increased precipitation over the southern tropical oceans. However, the decline in Southern Hemisphere insolation during austral summer induces a significant cooling over land, which in turn weakens the land-sea temperature contrast, leading to an overall reduction (−20 %) in monsoonal precipitation over the Southern Hemisphere's continental regions. The intensity and areal extent of the Australian, South American and South African monsoons are consistently reduced. This is associated with greater pressure and subsidence over land due to a strengthening of the southern hemispheric Hadley cell during austral summer.

Global ionosonde and GPS radio occultation sporadic-E intensity and height comparison

2020 ◽  
Vol 199 ◽  
pp. 105200
Author(s):  
Joshua Y. Gooch ◽  
Jonah J. Colman ◽  
Omar A. Nava ◽  
Daniel J. Emmons
Keyword(s):  
Radio Occultation ◽  
Gps Radio Occultation ◽  
Sporadic E

Global Sporadic E Layer Characteristics Obtained from GPS Radio Occultation Measurements

2013 ◽  
pp. 207-221 ◽  
Author(s):  
Christina Arras ◽  
Jens Wickert ◽  
Christoph Jacobi ◽  
Georg Beyerle ◽  
Stefan Heise ◽  
...  
Keyword(s):  
Radio Occultation ◽  
Gps Radio Occultation ◽  
Sporadic E Layer ◽  
Sporadic E

Simulated GPS radio occultation signals from sporadic-E layers

2020 ◽  
Author(s):  
Daniel Emmons
Keyword(s):  
Radio Occultation ◽  
Plasma Frequency ◽  
Signal Amplitude ◽  
Scintillation Index ◽  
Gps Radio Occultation ◽  
Multiple Phase ◽  
Maximum Variance ◽  
Sporadic E Layers ◽  
Sporadic E ◽  
Screen Model

&lt;p&gt;A multiple phase screen model is used to simulate GPS radio occultation signals through varying sporadic-E layers.&amp;#160; The length, vertical extent, and plasma frequency of the sporadic-E layers are varied to analyze the effect on the signal received by a low earth orbiting satellite.&amp;#160; A nonlinear relationship between the maximum variance in the signal amplitude and the plasma frequency is observed.&amp;#160; For certain frequency ranges, the predictions match previous studies that have used the S&lt;sub&gt;4 &lt;/sub&gt;scintillation index to predict fbEs values. Additionally, the spectra of the signals are analyzed as a function of the different parameters providing an alternative approach for extracting sporadic-E parameters from GPS radio occultation measurements.&amp;#160;&lt;/p&gt;

Effect of sporadic E clouds on GPS radio occultation signals

2010 ◽  
Vol 37 (18) ◽  
pp. n/a-n/a ◽  
Author(s):  
Z. Zeng ◽  
S. Sokolovskiy
Keyword(s):  
Radio Occultation ◽  
Gps Radio Occultation ◽  
Sporadic E
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