Sporadic E seasonal variability and descent derived from GPS-

COSMIC Radio Occultation

1Department of Physics, Chinese Culture University, Taipei, Taiwan, R.O.C.2Institute of Space Science, National Central University, Chung-Li, Taiwan, R.O.C.

Chien-Ya Wang1 and Yen-Hsyang Chu2

23 June 2010 CEDAR

Contents:1. Occurrence rates of sporadic E(Es) from

COSMIC RO data in 3 years.

2. Vertical tidal wavelengths estimate at different latitudes from Es occurrence rate profiles.

3. Probably a case of diurnal tide in Es region detected by Chung-Li VHF radar.

Motivation:

Variance analyze COSMIC RO (radio occultation) in Es region data to explore the Es phenomena.

► Recently, GPS radio occultations (RO) are used to study irregularities in the lower ionospheric E region [Wu et al.,2005; Arras et al.,2008]. This allows for global maps of sporadic E occurrence rates of high spatial resolution.

► If there are electron density irregularities existed in the ray path, the scintillation and multiple paths effects will disturb the received GPS signals. Thus from the analysis of these disturbed signals, Es layer can be defined.

► Statistics of COSMIC RO data from 2006 Jul.~2009 Aug. will be presented. In this report will focus on the comparing with the idealized tide wind function in different latitudes.

Introduction

Examples of Identifying Es layer from GPS Phase/SNR Profiles

R:3-point running meanB: Raw data

Red points indicate the peak perturbed, for those values of L2 and two SNRs have the same height of L1 are selected.

80 km

130 km

Es region

SNR 0

127.8615°W 9.2593°S

A high pass filter is applied to SNR1 and SNR2 , then normalize with background SNR01 and SNR02.

Two high pass filter processes are applied to L1 and L2.

L1 L2 SNR1 SNR2

Occurrence Rate of Four Seasons from 2006 Jun.-2009 Aug.

Grid Resolution

5°×5°

Spring Summer

Fall Winter

UU

I

dt

dz

ii

ii

2/1

cos/

angledipmagneticI

ionofncygyrofreque

frequencycollisionneutralion

windzonalU

windmeridionalV

i

i

:

:

:

:

,:

phaset

periodT

wavelengthvertical

heightscaleH

z

:

:

:

:

0

),,(),,,( 0v

,vv

VUUwvu

UMBe

ni

niini

Wind shear theory with diffusion and E-field are neglected

Theory

000

022

cos2

exp ttT

zzH

zzU

dt

dz

z

000

022

cos2

exp ttT

zzH

zzUU

z

Simulation with ideal zonal wind

kmzkmH 95,5.5 0

0,24,15 0 thrTkma z

000

022

cos2

exp ttT

zzH

zzU

dt

dz

z

hrthrTkmb z 4,12,30 0

Fit to mid-night diurnal

Fit to noontime semidiurnal

Local Time (hr)

Summer (2006-2008)

5 N

10 N

15 N

20 N

25 N

30 N

35 N

40N

45 N

50 N

55 N

60 N

Winter (2006-2008)

5 S

10 S

15 S

20 S

25 S

30 S

35 S

40 S

45 S

50 S

55 S

60 S

Diurnal tide

Vertical wavelengths estimated from ideal tidal function

Es exist in negative zonal wind shear convergence region

20°N spring 50°N summer

Wind shear contour from HWM07 model

May 20

May 21

May 22

May 23

May 24

RTI plots of Chung-Li 30MHz radar Es echoes at May 20-24 2008

Es exist in negative zonal wind shear convergence region

hrTkmzkmH 24,95,5.5 0

hrtkmz 10,25 0

000

022

cos2

exp ttT

zzH

zzU

dt

dz

z

A diurnal tide ?

Summery:• Seasons morphology of Es occurrence rates from

COSMIC data show two explicit semidiurnal tides start (from midnight and noontime ) in latitude 20°~60°N.

• The vertical wavelengths of semidiurnal tides are varies in 20~45 km, while the diurnal tide wavelengths in law latitude(5°~15°N) are ~15 km.

• Sporadic E echoes exist in negative zonal wind shear region, exhibit a candidate of diurnal tide with vertical wavelength ~25km are detected by Chung-Li radar.

Thank you!