Meteorological Impacts on Space Weather

Jan Laštovička

Institute of Atmospheric Physics, Bocni II, 14131 Prague, Czech Republic; jla@ufa.cas.ca

Meteorological processes in the lower-lying layers, particularly in the troposphere, affect the ionosphere mainly through upward propagating waves, i.e. on time scales of space weather processes. Those waves are planetary waves, tidal waves, gravity waves, and less known infrasonic waves.

Outline:

1. Tides

2. Planetary waves

3. Gravity waves

4. Infrasonic waves (infrasound)

5. Conclusions

Tides

Lunar tides – gravitational origin.

Solar tides – thermal origin.

Diurnal, semidiurnal, terdiurnal (other) tides (T = 24, 12, 8 (less) hours). Migrating and non-migrating tides. Generated in situ and propagating from below.

MLT region (80-100 km) winds – semidiurnal and diurnal tides are relatively often stronger than prevailing wind.

In northern Scandinavia (EISCAT – high latitudes), the terdiurnal tide dominates in the E-region, particularly in ion and electron temperatures (e.g., Hocke, Ann. Geophysicae 14, 201, 1996).

Diurnal and semidiurnal tides are of fundamental importance for formation of the midlatitude Es layers due totheir vertical wind shear (Haldoupis et al., JGR 109, A04304, 2004).

Tides – F2 region

At F2 region heights (h > 200 km), both models and observations show a tendency of tides to maintain constancy with height, mainly due to the dominance of molecular diffusion, and diurnal tidal winds exhibit less day-to-day variability than in the MLT region (e.g. Forbes, JGR 87, 5222, 1982).

Model calculations by Fesen (JASTP 59, 1521, 1997) revealed the effects of diurnal tides vertically propagating from the lower atmosphere on the F2 layer maximum electron density (NmF2) and height (hmF2) – in NmF2 of the order of 10-20% during the daytime and as much as 40% during the nighttime at low latitudes. The lower atmosphere waves introduced also semidiurnal oscillations into hmF2. Such strong effects were modeled for the low solar activity conditions. Under the high solar activity conditions, tides do not penetrate so deep into the thermosphere and a weaker effect in the F2 layer parameters is expected. The NmF2 perturbations are ultimately due to chemical effects, i.e. by changes in the concentration of N2 and O2 caused by displacement of the F layer by 10 to 20 km.

Planetary waves (PW)

Planetary waves of tropospheric origin have been observed to penetrate up to about 110 km at least in winter (e.g. Vincent, ASR, 10(12), 93, 1990), but they cannot penetrate directly to F-region heights. Planetary wave-like oscillations (T = 2-30(35) days) have been observed in:The lower ionosphere (radio wave absorption).E-region (foE).F2-region (foF2, hmF2, N(h)-profiles).

Ionospheric PW-type oscillations are assumed to reflect the PW-type oscillations in the neutral atmosphere (confirmed by model calculations for the lower ionosphere).

PW – lower ionosphere (h < 100 km)

PW activity in terms of maximum amplitudes of absorption oscillations, T ~ 5 and 10 days, the 1970s and 1980s, 1412 kHz, Bulgaria. Seasonal variation and trend.

PW – E-region

PW-type oscillations were observed in:

E-layer critical frequency foE – e.g., Cavalieri, JATP 38, 965, 1976.

Sporadic-E layer – e.g. Pancheva et al., JGR 108 (A5), 1176, doi: 10.1029/2002JA009788, Haldoupis et al., JGR 109, A04304, 2004. Planetary waves were found to play a role in Es-layer formation, but predominantly indirectly through a strong non-linear modulation of semidiurnal and diurnal tides by planetary waves at heights below 100 km.

PW – F-region

Planetary waves cannot penetrate directly to F-region heights. Therefore, indirect upward propagation via planetary wave modulation of various upward propagating agents at upper mesospheric/lower thermospheric heights:

Vertical plasma drift – due to planetary wave modulation of E-region dynamo (e.g. Pancheva et al., 1994).

Tides – some role confirmed by Lastovicka and Sauli (1999 – observations) and Mueller-Wodarg (modelling for the 2-day wave).

Gravity waves (e.g. Meyer, JGR, 104(A12), 1999).

Turbopause height and turbopause region properties or composition changes at the base of the thermosphere.

PW – F-regionAmplitudes of 5-day (short-dashed line), 10-day (medium-dashed line), 13.5-day (full line) and 16-day (long-dashed line) oscillations in foF2 for Kaliningrad; F10.7 is for solar activity. Amplitudes in average ~5%. Solar cycle – solar minimum, summer, PW negligible; solar maximum, winter, amplitude up to more than 1 MHz.

PW – F-region

Origin of PW-type fluctuations (Altadill et al., 2004): The drivers may be:- the PW activity in the MLT region, - the quasi-periodic geomagnetic activity, - the PW-type events ‘independent’ of the above two, - and a very small contribution of solar flux variations.

PW - persistence

Morlet wavelet – absolute and relative evaluation

Statistics of persistence of PW type oscillations in foF2 over Europe. The values for medians and the most frequent values are presented with step 0.5. In Japan and US foF2 similar, as well as in European lower ionosphere. Shorter period PW are more persistent in terms of wave cycles, less persistent in terms of days.

PW - persistence

Station Period (days)

Number of events

Median value

Mean value

Most frequent

value

Average values - Europe

5 40 4 4.3 4

10 36 3.5-4 3.9 3.5

16 32 3.5 3.7 3

PW – longitudinal size of events in foF2

Altadill and Apostolov (2003, JGR, A11) found typical longitudinal size of PW-type events in foF2 to be:

T = 5-6 days, 80o T = 10 days, 100o

T = 16 days, 180o, with individual events covering up to the whole globe.

This is consistent with our result of full dissimilarity of 5-day events in Europe, Japan and US, and with very limited similarity of 7-day events.

10-day events are also largely dissimilar, as corresponds to their typical size of 100o.

16-day events show much higher degree of similarity between European, US and Japanese stations (foF2), which is consistent with their larger typical size.

PW – N(h)-profiles

Fagundes et al. (JGR 110, A12302, 2005) used N(h)-profiles from ionosonde at São José dos Campos, Brazil (southern crest of EIA), June-September 2003. They found:

1. PW-like wave presence at different F region heights.

2. Best expressed in variations of virtual heights for fixed frequencies, sometimes with amplitudes > 50 km.

3. Basic tropospheric PW periods were found at F region heights – about 2-, 5-, 10 and 16-day.

Gravity waves (GW)

Gravity waves are of principal importance for the mesosphere and mesopause region and, therefore, are important for the lower ionosphere – GWs predominantly coming from below (troposphere, partly stratosphere).

In the F-region they are important, as well. Among others they create the travelling ionospheric disturbances (TIDs). GWs in the F region may be of different origin: (a) excited at high latitudes by geomagnetic/auroral activity, (b) coming from below (“meteorological” origin, explosive phenomena at surface), (c) excited in situ by the solar terminator passages, solar eclipses, etc.

GW – lower ionosphere

W inters

0 .0

4 .0

8 .0

GW

rel

ativ

e am

plitu

de (

%)

+ R

/16 R

P INAT

1988/89 1994/95

aerosol

GW activity (relative amplitudes) for period bands (from bottom to top) - 10-30 min, 31-60 min, 61-90 min, 91-120 min, 121-150 min and 151-180 min in winters 1988/89-1994/95. R - sunspot number; aerosol – quasi-local aerosol optical depth; PINAT - Mt. Pinatubo volcanic eruption. Effects of solar activity and Pinatubo eruption.

GW – E region

GWs play some role in forming the sporadic-E and layered structures in the E region (Fukao et al., GRL 25, 1761, 1998; Matthews, JASTP 60, 413, 1998; Roddy et al., JGR 112, A06312, 2007) – via enhanced irregular neutral wind due to GW (Parkinson and Dyson, JASTP 60, 509, 1998). GWs were found to cause a vertical motion of Es-layers (Bourdillon et al., Ann. Geophysicae 15, 925,1997). Some features of Es-layers were simulated only when gravity waves were taken into account (Huang and Kelley, JGR 101, 24533,1996).

GW-type oscillations may sometimes be caused by quasi- periodic particle precipitation (Rinnert, Ann. Geophysicae 14, 707,1996).

GW – F region – in situ - eclipseVertical structure of a GW event, solar eclipse of 11 August 1999, Průhonice (49.9ºN, 14.5ºE) – vertical phase and group velocities of the wave packet, dominant period of 85 minutes, as a function of altitude. Adapted from Šauli (PhD thesis, 2001).

Upward and downward propagation from a source region at ~180-200 km.

GW – F region – from belowVertical structure of a GW event excited by a cold front, 2 November 1997, Ebro (40.8ºN). Left panel - vertical phase and group velocities, wave packet with dominant T = 75 min. Right panel - the disturbance excited by GWs in the plasma frequency; black line - energy progression of the wave, average velocity of 8 ms-1; white lines - phase progression with average velocity of -47 ms-1. Adapted from Altadill et al. (1999).

Upward propagating GW.

GW – F region – from below

Meteorological processes are a quasi-permanent source of GWs coming from below (mainly from the troposphere, partly also from the stratosphere). Cold fronts belong to the strongest midlatitude GW sources. GWs of “meteorological” origin belong to sources of uncertainty and inaccuracy in ionospheric radio wave forecasting.

There are other sources of GWs coming from below, but they are sporadic, like earthquakes, volcanic eruptions and big explosions etc.

Infrasound – upward propagationPeriod range of about 1 second to a few minutes.

Dependence of refractive coefficient on the altitude for the real atmosphere (a) and directional radiation pattern of a point acoustic

source (b). Waves turn upwards.

0 .2 0 .4 0 .6 0 .8 1 1 .2 1 .4refra ctiv e co efficien t

0

1 0 0

2 0 0

3 0 0

4 0 0

h, k

m

-800 -400 0 400 800d , k m

0

100

200

300

400

h, k

m

7 0 70

Conclusions

Wave forcing from below is very important for the upper atmosphere and ionosphere. It acts on the same time scales from seconds to days as space weather phenomena.

In spite of progress, various open questions remain, for example:Role/importance of infrasoundHow planetary waves penetrate to F-region heightsQuantification of the role of gravity waves