DMSP Satellites Research Articles

Precipitation products from the hydrology SAF

Abstract. The EUMETSAT Satellite Application Facility on Support to Operational Hydrology and Water Management (H-SAF) was established by the EUMETSAT Council on 3 July 2005, starting activity on 1 September 2005. The Italian Meteorological Service serves as Leading Entity on behalf of twelve European member countries. H-SAF products include precipitation, soil moisture and snow parameters. Some products are based only on satellite observations, while other products are based on the assimilation of satellite measurements/products into numerical models. In addition to product development and generation, H-SAF includes a product validation program and a hydrological validation program that are coordinated, respectively, by the Italian Department of Civil Protection and by the Polish Institute of Meteorology and Water Management. The National Center of Aeronautical Meteorology and Climatology (CNMCA) of the Italian Air Force is responsible for operational product generation and dissemination. In this paper we describe the H-SAF precipitation algorithms and products, which have been developed by the Italian Institute of Atmospheric Sciences and Climate (in collaboration with the international community) and by CNMCA during the Development Phase (DP, 2005–2010) and the first Continuous Development and Operations Phase (CDOP-1, 2010–2012). The precipitation products are based on passive microwave measurements obtained from radiometers onboard different sun-synchronous low-Earth-orbiting satellites (especially, the SSM/I and SSMIS radiometers onboard DMSP satellites and the AMSU-A + AMSU-B/MHS radiometer suites onboard EPS-MetOp and NOAA-POES satellites), as well as on combined infrared/passive microwave measurements in which the passive microwave precipitation estimates are used in conjunction with SEVIRI images from the geostationary MSG satellite. Moreover, the H-SAF product generation and dissemination chain and independent product validation activities are described. Also, the H-SAF program and its associated activities that currently are being carried out or are planned to be performed within the second CDOP phase (CDOP-2, 2012–2017) are presented in some detail. Insofar as CDOP-2 is concerned, it is emphasized that all algorithms and processing schemes will be improved and enhanced so as to extend them to satellites that will be operational within this decade – particularly the geostationary Meteosat Third Generation satellites and the low-Earth-orbiting Core Observatory of the international Global Precipitation Measurement mission. Finally, the role of H-SAF within the international science and operations community is explained.

Advantages of the new model of IRI (IRI-Plas) to simulate the ionospheric electron density: case of the European area

Abstract. Satellite telecommunications, positioning and navigation systems require knowledge of the electron distribution in height Ne(h) to high-altitude orbits of satellites. One of the possibilities to construct such profiles is associated with the use of the ionospheric total electron content TEC. This paper is devoted to three advantages of the IRI-Plas model. They include introduction of the topside basis scale height Hsc, expansion of the IRI model to the plasmasphere, ingestion of experimental values of TEC. Testing of this model according to different satellite experiments (CHAMP, DMSP) shows the high efficiency of this model. The method of adaptation of the IRI-Plas model to the plasma frequency at altitudes of CHAMP and DMSP satellites allows us to produce behavior of Ne(h)-profiles during the disturbances, as well as to refine the values of TEC, which determine the accuracy of positioning. Results were obtained using data of the European area.

TEC evidence for near‐equatorial energy deposition by 30 keV electrons in the topside ionosphere

Observations of energetic electrons (10 – 300 keV) by NOAA/POES and DMSP satellites at heights <1000 km during the period from 1999 to 2010 allowed finding abnormal intense fluxes of ~106 – 107 cm−2 s−1 sr−1 for quasi‐trapped electrons appearing within the forbidden zone of low latitudes over the African, Indo‐China, and Pacific regions. Extreme fluxes appeared often in the early morning and persisted for several hours during the maximum and recovery phase of geomagnetic storms. We analyzed nine storm time events when extreme electron fluxes first appeared in the Eastern Hemisphere, then drifted further eastward toward the South‐Atlantic Anomaly. Using the electron spectra, we estimated the possible ionization effect produced by quasi‐trapped electrons in the topside ionosphere. The estimated ionization was found to be large enough to satisfy observed storm time increases in the ionospheric total electron content (TEC) determined for the same spatial and temporal ranges from global ionospheric maps. Additionally, extreme fluxes of quasi‐trapped electrons were accompanied by the significant elevation of the low‐latitude F‐layer obtained from COSMIC/FORMOSAT‐3 radio occultation measurements. We suggest that the storm time ExB drift of energetic electrons from the inner radiation belt is an important driver of positive ionospheric storms within low‐latitude and equatorial regions.

An interhemispheric comparison of GPS phase scintillation with auroral emission observed at the South Pole and from the DMSP satellite

<p>The global positioning system (GPS) phase scintillation caused by high-latitude ionospheric irregularities during an intense high-speed stream (HSS) of the solar wind from April 29 to May 5, 2011, was observed using arrays of GPS ionospheric scintillation and total electron content monitors in the Arctic and Antarctica. The one-minute phase-scintillation index derived from the data sampled at 50 Hz was complemented by a proxy index (delta phase rate) obtained from 1-Hz GPS data. The scintillation occurrence coincided with the aurora borealis and aurora australis observed by an all-sky imager at the South Pole, and by special sensor ultraviolet scanning imagers on board satellites of the Defense Meteorological Satellites Program. The South Pole (SP) station is approximately conjugate with two Canadian High Arctic Ionospheric Network stations on Baffin Island, Canada, which provided the opportunity to study magnetic conjugacy of scintillation with support of riometers and magnetometers. The GPS ionospheric pierce points were mapped at their actual or conjugate locations, along with the auroral emission over the South Pole, assuming an altitude of 120 km. As the aurora brightened and/or drifted across the field of view of the all-sky imager, sequences of scintillation events were observed that indicated conjugate auroras as a locator of simultaneous or delayed bipolar scintillation events. In spite of the greater scintillation intensity in the auroral oval, where phase scintillation sometimes exceeded 1 radian during the auroral break-up and substorms, the percentage occurrence of moderate scintillation was highest in the cusp. Interhemispheric comparisons of bipolar scintillation maps show that the scintillation occurrence is significantly higher in the southern cusp and polar cap.</p>

Observation of F region irregularities near a northern equatorial anomaly crest during solar minimum using ionosonde, GPS receiver, and satellites

For solar minimum, the spread F, GPS phase fluctuations, and plasma bubbles near the crest of equatorial ionization anomaly (EIA) are simultaneously analyzed to investigate F region irregularities for the first time. The data were observed using the Chungli ionosonde, YMSM GPS receiver, and DMSP satellites during 1996. It is found that in the observed ionograms, the frequency spread F (FSF) usually comes after the range spread F (RSF) in a series of nighttime spread F events. This results in that the maximum occurrence of RSF appears before that of FSF in the nighttime variations in occurrence probabilities. Moreover, the seasonal variation for RSF is close to that for FSF. Both have a board maximum in the J‐months and a secondary maximum in December. These indicate that RSF and FSF should be regarded as one type of spread F, which is the all spread F (ASF) in this study. Because the equatorial plasma bubbles occur infrequently during solar minimum, the F region irregularities forming ASF are not related to the equatorial spread F. On the other hand, the similarity in seasonal occurrence between ASF and medium‐scale traveling ionospheric disturbances (MSTIDs) demonstrates that the F region irregularities near the EIA crest are mainly generated by the gradient drift instability driven by MSTIDs. The irregularities, generated by MSTIDs, mostly occur in the bottom side of the F region. Consequently, the events of significant GPS phase fluctuations and plasma bubble near the EIA crest are rare during 1996.

Comparison of topside electron density computed by ionospheric models and plasma density observed by DMSP satellites

Electron density obtained by IRI (topside options NeQuick and IRI-Corr) and NeQuick models in their standard versions have been compared with plasma density values measured by F13 and F15 DMSP satellites for years of different solar activities. A statistical study of the differences between modeled and experimental data has been carried out to investigate each model performance.In general, the models present a similar behavior. Nevertheless it has been found that the IRI-Corr topside option of IRI overestimates electron density at high latitudes and this trend increases with the solar activity.A few examples of representative half-orbit passes are given to illustrate the differences found.

Evolution of auroral acceleration types inferred from two‐satellite coincidences

The relationship between monoenergetic electron acceleration and broadband electron acceleration is uncertain, although some have speculated that the latter is a temporal transient, and may evolve into the former. Here we have taken advantage of DMSP satellite coincidences to investigate the issue. We consider 1668 cases where one DMSP satellite observed an electron acceleration event covering at least 2 s, hence as many discrete accelerated spectra, and a second satellite subsequently observed an electron acceleration at the same location. The spatial coincidence required was tight, with a maximum separation of 0.1° magnetic latitude and 0.15 h magnetic local time. Time separations of 0–10 min were considered in 1 min bins, with auroral acceleration flagged as either monoenergetic, broadband, or a mixture of both. Within the first temporal bin (0–1 min), the second satellite had a high probability of observing the same type of aurora as the first, establishing consistency. When the first satellite observed monoenergetic aurora, the second satellite also observed monoenergetic aurora (about 80% of the time), and this continued to up to about 10 min of UT separation. In most of the other 20% of the cases, the second satellite also recorded monoenergetic acceleration but with an additional mixture of broadband acceleration. Thus monoenergetic aurora does not seem to typically evolve on a time scale of minutes. However, when the first satellite encounter was with broadband acceleration, the second encounter was highly time‐dependent, with broadband dominating the second satellite encounter only in the 0–1 min bin. Between 1 and 5 min, the probability of observing a mixture of auroral types jumped, and after 6 min, the auroral acceleration was nearly as likely to be monoenergetic as broadband. Finally, if the first satellite encountered a mixture of acceleration, the second encounter was progressively more likely to be entirely monoenergetic aurora as time increased. These results are consistent with the idea that broadband aurora may be inherently a transient, and often progresses to monoenergetic aurora, while the latter is quasi‐static.

Temporal and spatial effects of subauroral polarization streams on the thermospheric dynamics

Based on two years of Subauroral Polarization Streams (SAPS) events detected by DMSP satellites in the dusk‐premidnight sector, we have studied the temporal and spatial effects of SAPS on thermospheric quantities. The events are divided into two different MLT (magnetic local time) groups covered by F13 and F14/15. Concurrent CHAMP observations taken between −30° and +60° in longitude (−2 h and +4 h MLT) with respect to the SAPS detection location and within a time window of 1.5 h before and 3 h after the SAPS detection time are used for comparison. For the first time the spatial and temporal effects of SAPS are shown. SAPS have great influences on the zonal wind in all MLT bins (17–21 MLT) around the F13 MLT sector, with the largest effect appearing around 19 MLT, about 0–2 hours MLT after SAPS onset. SAPS have relatively little effect around 23–24 MLT, as deduced from F14/15 SAPS. For most cases the zonal wind peaks in the first orbit, concurrent with the SAPS onset. But around 19 MLT the zonal wind attains peak velocities about 1.5 h after the SAPS detection. This is claimed to be related to the longer persistence of SAPS events in this MLT sector than in other sectors. The background air density gets enhanced by SAPS with the most prominent variation occurring around 19 MLT. There are density bulges appearing around the SAPS latitude. The electron density trough gets deepened and attains the minimum in the first orbit after the SAPS onset. The largest depletion can also be found around 19 MLT. Both the eastward and westward Hall currents (electrojets) get strengthened right after SAPS onset. The zonal wind peaks 2°–3° in latitudes equatorward of the eastward electrojet.

Evaluation of precipitation detection over various surfaces from passive microwave imagers and sounders

During the middle part of this decade, a wide variety of passive microwave imagers and sounders will be unified in the Global Precipitation Measurement (GPM) mission to provide a common basis for frequent (3h) global precipitation monitoring. The ability of these sensors to detect precipitation by discerning it from non-precipitating background depends upon the channels available and characteristics of the surface and atmosphere. This study quantifies the minimum detectable precipitation rate and fraction of precipitation detected for four representative instruments (TMI, GMI, AMSU-A, and AMSU-B) that will be part of the GPM constellation. Observations for these instruments were constructed from equivalent channels on the SSMIS instrument on DMSP satellites F16 and F17 and matched to precipitation data from NOAA's National Mosaic and QPE (NMQ) during 2009 over the continuous United States. A variational optimal estimation retrieval of non-precipitation surface and atmosphere parameters was used to determine the consistency between the observed brightness temperatures and these parameters, with high cost function values shown to be related to precipitation.The minimum detectable precipitation rate, defined as the lowest rate for which probability of detection exceeds 50%, and the detected fraction of precipitation are reported for each sensor, surface type (ocean, coast, bare land, snow cover) and precipitation type (rain, mix, snow). The best sensors over ocean and bare land were GMI (0.22mmh−1 minimum threshold and 90% of precipitation detected) and AMSU (0.26mmh−1 minimum threshold and 81% of precipitation detected), respectively. Over coasts (0.74mmh−1 threshold and 12% detected) and snow-covered surfaces (0.44mmh−1 threshold and 23% detected), AMSU again performed best but with much lower detection skill, whereas TMI had no skill over these surfaces. The sounders (particularly over water) benefited from the use of re-analysis data (vs. climatology) to set the a priori atmospheric state and all instruments benefited from the use of a conditional snow cover emissivity database over land. It is recommended that real-time sources of these data be used in the operational GPM precipitation algorithms.

The pulsed nature of the nightside contribution to polar cap convection: repetitive substorm activity under steady interplanetary driving

Abstract. The aim of this study is to investigate the relative contributions of dayside and nightside processes to the spatial and temporal structure of polar cap plasma convection. The central parameter is the cross-polar cap potential (CPCP). Selecting a 10-h-long interval of stable interplanetary driving by an interplanetary CME (ICME), we are able to distinguish between the dayside and nightside sources of the convection. The event was initiated by an abrupt enhancement of the magnetopause (MP) reconnection rate triggered by a southward turning of the ICME magnetic field. This was followed by a long interval (10 h) of steady and strong driving. Under the latter condition a long series of electrojet intensifications was observed which recurred at 50 min intervals. The detailed temporal structure of polar cap convection in relation to polar cap contraction events is obtained by combining continuous ground observations of convection-related magnetic deflections (including polar cap magnetic indices in the Northern and Southern Hemispheres, PCN and PCS) and the more direct, but lower-resolution ion drift data obtained from a satellite (DMSP F13) in polar orbit. The observed PCN enhancements combined with DMSP satellite observations (F13 and F15 data) of polar cap contractions during the evolution of selected substorm expansions allowed us to estimate the CPCP enhancements (25%) associated with individual events in the series. Ground-satellite conjunctions are further used to investigate the spatial structure of polar cap convection, i.e., the homogeneous plasma flow in the centre (Vi ≤ 1 km s−1) versus channels of enhanced antisunward flows (Vi ≥ 1 km s−1) along the periphery of the polar cap. We emphasise the temporal structure of these polar cap flow phenomena in relation to the prevailing solar wind forcing and the repetitive substorm activity.

Artificial ducts caused by HF heating of the ionosphere by HAARP

We report on satellite observations of plasma density enhancements (ducts) in the topside ionosphere during four HAARP/BRIOCHE campaigns during 2009–2010. Artificial ducts, caused by high‐power HF radio wave injections from the HAARP transmitter toward the magnetic zenith, are detected by the DEMETER and DMSP satellites on a regular basis when there is a perceptible ionospheric F2 peak density. Overall, the plasma density enhancements detected between 0930 and 1230 LT varied from 3–13%, while those during ∼1730–2215 LT were typically 15–40%. We also used a modified SAMI2 model to study the artificial ducts' mechanism driven by HF electron heating in the bottomside F2 region. The heating builds up the plasma pressure, thus pushing plasma along the magnetic field. The simulation results performed for the input parameters similar to the conditions of the heating experiments are in fair agreement with the pertinent observations. The ducts seem to be produced most efficiently for heating frequencies quite close to the critical frequency foF2.

Impact of Precipitation Rate Assimilation over India and Surrounding Regions

An Observation System Experiment has been described that examines the impact of precipitation rate, obtained from SSM/I onboard the DMSP satellites and those from the TRMM. Analysis scheme used is Gridpoint Statistical Interpolation (GSI) with the forecast model T254L64. Analyses are carried out globally for four times daily at six hourly intervals from 00z to 18z. Two sets of simulations were performed. Precipitation rate measured by SSM/I and TRMM are assimilated and subsequently forecasts for 168 hour are made through the NCMRWF’s GFS for the entire month of June-2009. The analyses and forecasts are also repeated for the entire period without assimilating the precipitation rate data. The results are analyzed globally giving special emphasis over India and surrounding regions. When compared with the observations, improvement of analyses and forecasts from experimental simulations were noticed. Analyses versus observation study showed improvement in terms of lower RMSE over both Tropics and Indian region. Positive impact on temperature analysis is seen over all the three levels of 850, 500 and 250hPa. For vector wind and geo-potential height analysis positive impact of assimilation is seen over 500 and 250hPa pressure levels. In forecast versus analysis comparison, the differences in the values from the two simulations are mostly insignificant. For a few cases, the experimental simulations shows significant improvement over the control runs. When compared with the observations, consistent improvement in the experimental forecast in terms of lower RMSE is found over both Tropics and Indian region. Improvement in all the three parameters (temperature, horizontal wind and geo-potential height) is observed.

Enhanced energetic electron fluxes at the region of the auroral oval during quiet geomagnetic conditions November 2009

Enhanced fluxes of subrelativistic electrons were studied using the CORONAS-PHOTON satellite data during November 2009. During this time interval quiet geomagnetic conditions were unusually quiet. It was found that for more than 50% of all events, the enhanced fluxes with very similar characteristics were observed at two or more consecutive orbits, i.e. have a life time of a few hours. The analysis of relative location of enhanced fluxes and auroral particle precipitations, measured simultaneously by the low orbiting METEOR-M and DMSP satellites, showed that the enhanced fluxes are located inside the auroral oval, i.e. poleward from the external boundary of the outer electron radiation belt. This fact was also confirmed comparing these fluxes with the auroral oval boundaries provided by the OVATION model of auroral precipitations. The nature of the observed events is discussed.

The relation between subauroral polarization streams, westward ion fluxes, and zonal wind: Seasonal and hemispheric variations

We investigate the seasonal variation of the relation between SAPS (subauroral polarization streams) peak ion velocity and zonal wind velocity with coordinated DMSP and CHAMP satellite observations in both hemispheres, separately for Kp < 4 and Kp ≥ 4 geomagnetic conditions. Both SAPS and westward zonal wind peak almost at the same latitude. However, SAPS and zonal wind peak velocities show significantly different seasonal variations. SAPS peak velocities are larger in winter as compared to summer, while zonal wind peak velocities have opposite behavior, larger in summer and smaller in winter, which is valid in both hemispheres and for both geomagnetic activity levels. We reveal, for the first time, that SAPS peak westward ion fluxes, the product of SAPS ion velocity and ion density, exhibit similar seasonal variation as the zonal wind. The results indicate that the effect of SAPS on the zonal wind depends strongly on local ion densities. A linear relationship between SAPS ion fluxes and zonal wind is derived for both hemispheres, which is practically independent of geomagnetic activity. The scaling factor between ion flux and wind velocity is about the same in both hemispheres. Conversely, the background westward wind velocity (bias value in linear equation) is by about 100 m/s higher in the Northern than in the Southern Hemisphere. We attribute this difference to the effect of the large offset between geographic and magnetic poles in the Southern Hemisphere.

Interhemispheric comparison of GPS phase scintillation at high latitudes during the magnetic-cloud-induced geomagnetic storm of 5–7 April 2010

Abstract. Arrays of GPS Ionospheric Scintillation and TEC Monitors (GISTMs) are used in a comparative scintillation study focusing on quasi-conjugate pairs of GPS receivers in the Arctic and Antarctic. Intense GPS phase scintillation and rapid variations in ionospheric total electron content (TEC) that can result in cycle slips were observed at high latitudes with dual-frequency GPS receivers during the first significant geomagnetic storm of solar cycle 24 on 5–7 April 2010. The impact of a bipolar magnetic cloud of north-south (NS) type embedded in high speed solar wind from a coronal hole caused a geomagnetic storm with maximum 3-hourly Kp = 8- and hourly ring current Dst = −73 nT. The interhemispheric comparison of phase scintillation reveals similarities but also asymmetries of the ionospheric response in the northern and southern auroral zones, cusps and polar caps. In the nightside auroral oval and in the cusp/cleft sectors the phase scintillation was observed in both hemispheres at about the same times and was correlated with geomagnetic activity. The scintillation level was very similar in approximately conjugate locations in Qiqiktarjuaq (75.4° N; 23.4° E CGM lat. and lon.) and South Pole (74.1° S; 18.9° E), in Longyearbyen (75.3° N; 111.2° E) and Zhongshan (74.7° S; 96.7° E), while it was significantly higher in Cambridge Bay (77.0° N; 310.1° E) than at Mario Zucchelli (80.0° S; 307.7° E). In the polar cap, when the interplanetary magnetic field (IMF) was strongly northward, the ionization due to energetic particle precipitation was a likely cause of scintillation that was stronger at Concordia (88.8° S; 54.4° E) in the dark ionosphere than in the sunlit ionosphere over Eureka (88.1° N; 333.4° E), due to a difference in ionospheric conductivity. When the IMF tilted southward, weak or no significant scintillation was detected in the northern polar cap, while in the southern polar cap rapidly varying TEC and strong phase scintillation persisted for many hours. This interhemispheric asymmetry is explained by the difference in the location of solar terminator relative to the cusps in the Northern and Southern Hemisphere. Solar terminator was in the immediate proximity of the cusp in the Southern Hemisphere where sunlit ionospheric plasma was readily convected into the central polar cap and a long series of patches was observed. In contrast, solar terminator was far poleward of the northern cusp thus reducing the entry of sunlit plasma and formation of dense patches. This is consistent with the observed and modeled seasonal variation in occurrence of polar cap patches. The GPS scintillation and TEC data analysis is supported by data from ground-based networks of magnetometers, riometers, ionosondes, HF radars and all-sky imagers, as well as particle flux measurements by DMSP satellites.

On relation between mid-latitude ionospheric ionization and quasi-trapped energetic electrons during 15 December 2006 magnetic storm

We report simultaneous observations of intense fluxes of quasi-trapped energetic electrons and substantial enhancements of ionospheric electron concentration (EC) at low and middle latitudes over the Pacific region during the geomagnetic storm on 15 December 2006. Electrons with energy of tens of keV were measured at altitude of ∼800–900km by POES and DMSP satellites. Experimental data from COSMIC/FS3 satellites and global network of ground-based GPS receivers were used to determine height profiles of EC and vertical total EC, respectively. A good spatial and temporal correlation between the electron fluxes and EC enhancements was found. This fact allows us to suggest that the quasi-trapped energetic electrons can be an important source of ionospheric ionization at middle latitudes during magnetic storms.

Dynamic subauroral ionospheric electric fields observed by the Falkland Islands radar during the course of a geomagnetic storm

[1] We present an analysis of ionospheric electric field data observed during a geomagnetic storm by the recently deployed HF radar located on the Falkland Islands. On 3 August 2010 at ∼1800 UT evidence of the onset of a geomagnetic storm was observed in ground magnetometer data in the form of a decrease in the Sym-H index of ∼100 nT. The main phase of the storm was observed to last ∼24 hours before a gradual recovery lasting ∼3 days. On 4 August, during the peak magnetic disturbance of the storm, a high velocity (>1000 m s−1) channel of ionospheric plasma flow, which we interpret as a subauroral ion drift (SAID), located between 53° and 58° magnetic south and lasting ∼6.5 hours, was observed by the Falkland Islands radar in the pre-midnight sector. Coincident flow data from the DMSP satellites and the magnetically near-conjugate northern hemisphere Blackstone HF radar reveal that the SAID was embedded within the broader subauroral polarization streams (SAPS). DMSP particle data indicate that the SAID location closely followed the equatorward edge of the auroral electron precipitation boundary, while remaining generally poleward of the equatorward boundary of the ion precipitation. The latitude of the SAID varied throughout the interval on similar timescales to variations in the interplanetary magnetic field and auroral activity, while variations in its velocity were more closely related to ring current dynamics. These results are consistent with SAID electric fields being generated by localized charge separation in the partial ring current, but suggest that their location is more strongly governed by solar wind driving and associated large-scale magnetospheric dynamics.

Comparison of Joule heating associated with high-speed solar wind between different models and observations

To gain an improved quantitative understanding of the solar wind/magnetosphere/ionosphere coupling processes, the capabilities of different models and observations to represent the variations of ionospheric forcing associated with high-speed solar wind streams are compared for year 2005. We investigate the high-latitude forcing from the measurements of DMSP satellite, empirical model Weimer05 and Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure, with ground magnetometer data only (AMIE 1) or with both ground magnetometer and DMSP convection data (AMIE 2). The yearly averages of the northern hemisphere integrated Joule heating (IJH) calculated from AMIE 1 and 2 are about 41% and 85% larger than that from Weimer05, respectively. A consistent 9-day periodicity is shown in both the cross polar cap potential and IJH, which corresponds to the 9-day oscillation in the high-speed solar wind streams. A band-pass filter centered at 9 day is used to examine the sensitivity of the IJH calculated from different sources to the solar wind condition. The comparison shows that the sensitivity of IJH from AMIE 1 and 2 are about 2.2 and 2.5 times larger than that from Weimer05, respectively.

A downward revision of a recently reported proton auroral LBH emission efficiency

[1] A significantly higher N2 Lyman-Birge-Hopfield (LBH) emission efficiency for auroral proton precipitation compared to model calculations was reported by Knight et al. (2008) based on a statistical study utilizing coincident far ultraviolet and particle data from the sensors Special Sensor Ultraviolet Spectrographic Imager (SSUSI) and Special Sensor J/5 (SSJ/5) on board the DMSP satellite F16. Here, the quantity of interest from that study is the median ratio of LBH column emission rates (CERs) from SSUSI and derived from SSJ/5 spectra using monoenergetic emission yields. The median ratio was found to be 2.83 for proton aurora, suggesting the need for significant increases in currently used LBH proton/H-atom impact cross sections. A key step in their analysis was extrapolation of SSJ/5 spectra above 30 keV. Limited testing of this algorithm using NOAA Polar Orbiting Environmental Satellites Total Energy Detector and Medium Energy Proton and Electron Detector (TM) data found no significant bias. This work reports on a more detailed investigation of the algorithm's performance, also using TM data, and has uncovered a bias that reduces the median column emission rates (CER) ratio to 1.75. Within expected uncertainties, including calibration, this still calls for cross section increases but to a lesser extent. The discovered bias becomes apparent with CER thresholding that was overlooked during testing by Knight et al. (2008). Thresholding at 400 Rayleighs (R) is necessary since Knight et al. excluded CERs < 400 R in deriving their median ratio. We show that the algorithm's performance degrades with increasing energy flux of the precipitation. A method is reported for eliminating most of the bias which utilizes auroral Ly α, whose emission strength is closely coupled to spectral hardness.

EstimatingDstindices and exospheric temperatures from equatorial magnetic fields measured by DMSP satellites

[1] We explore the feasibility of using variations in the horizontal component (ΔBH) of the Earth's magnetic field as measured by DMSP satellites while crossing the dip equator to estimate the provisional Dst index and the state of the thermosphere in near real time. Equatorial crossings are identified as locations where the vertical component of the main field measured by DMSP satellites vanishes. Local differences between measured and IGRF (epoch 2005) horizontal components (δBH) were calculated for the years 2005 to 2009. Each year quiet time (0 ≥ Dst ≥ – 7 nT) subsets of δBH were identified to establish offset baselines (δBH B) as functions of longitude along the magnetic equator (ϕeq) for each spacecraft. Year-to-year changes in δBH B reflect variations of the Earth's main field, indicating that baseline calculations must be updated at regular intervals for each spacecraft. Running-averaged values of ΔBH(t) = δBH (ϕeq, t) − δBH B (ϕeq, t) inferred from combined DMSP F16 and F17 data streams are shown to follow variations in Dst during the test interval. The method is also shown to apply during the magnetic superstorms of late 2003. Except during the late main phase, increases in globally averaged exospheric temperatures inferred from ΔBH and provisional Dst time series are in reasonable agreement with those inferred from measurements by accelerometers on the GRACE satellites.