Echo Layers Research Articles

Endoscopic ultrasound features of rectal melanoma: A case report and review of literature

BACKGROUND Rectal mucosal melanoma is a rare and highly aggressive disease. Common symptoms include anal pain, an anal mass, or bleeding. As such, the disease is usually detected on rectal examination of patients with other suspected anorectal diseases. However, due to its rarity and nonspecific symptoms, melanoma of the rectal mucosa is easily misdiagnosed. CASE SUMMARY This report describes the case of a 58-year-old female patient who presented with a history of blood in her stool for the prior one or two months, without any identifiable cause. During colonoscopy, a bulge of approximately 2.2 cm × 2.0 cm was identified. Subsequently, the patient underwent endoscopic ultrasound (EUS) to characterize the depth of invasion of the lesions. EUS suggested a hypoechoic mucosal mass with involvement of the submucosal layer and heterogeneity of the internal echoes. Following surgical intervention, the excised tissue samples were examined and confirmed to be rectal malignant melanoma. The patient recovered well with no evidence of recurrence during follow-up. CONCLUSION This case shows that colonoscopy with EUS and pathological examination can accurately diagnose rare cases of rectal mucosal melanoma.

High-frequency ultrasound in anti-aging skin therapy monitoring

Over the last few decades, high-frequency ultrasound has found multiple applications in various diagnostic fields. The fast development of this imaging technique opens up new diagnostic paths in dermatology, allergology, cosmetology, and aesthetic medicine. In this paper, being the first in this area, we discuss the usability of HFUS in anti-aging skin therapy assessment. The fully automated algorithm combining high-quality image selection and entry echo layer segmentation steps followed by the dermal parameters estimation enables qualitative and quantitative evaluation of the effectiveness of anti-aging products. Considering the parameters of subcutaneous layers, the proposed framework provides a reliable tool for TCA-peel therapy assessment; however, it can be successfully applied to other skin-condition-related problems. In this randomized controlled clinical trial, forty-six postmenopausal women were randomly assigned to the experimental and control groups. Women were treated four times at one-week intervals and applied skin cream daily between visits. The three month follow-up study enables measurement of the long-term effect of the therapy. According to the results, the TCA-based therapy increased epidermal (entry echo layer) thickness, indicating that the thinning process has slowed down and the skin’s condition has improved. An interesting outcome is the obtained growth in the intensity of the upper dermis in the experimental group, which might suggest a reduced photo-aging effect of TCA-peel and increased water content. The same conclusions connected with the anti-aging effect of TCA-peel can be drawn by observing the parameters describing the contribution of low and medium-intensity pixels in the upper dermis. The decreased share of low-intensity pixels and increased share of medium-intensity pixels in the upper dermis suggest a significant increase in local protein synthesis.

A novel rocket-borne ion mass spectrometer with large mass range: instrument description and first-flight results

Abstract. We present a novel rocket-borne ion mass spectrometer named ROMARA (ROcket-borne MAss spectrometer for Research in the Atmosphere) for measuring atmospheric positive and negative ions (atomic, molecular and cluster ions) and positively and negatively charged meteor smoke particles. Our ROMARA instrument has, compared to previous rocket-borne ion mass spectrometers, a markedly larger mass range of up to m/z 2000 and a larger sensitivity, particularly for meteor smoke particle detection. The major objectives of this first ROMARA flight included the following: a functional test of the ROMARA instrument, measurements between 55 and 121 km in the mass range of atmospheric positive and negative ions, a first attempt to conduct mass spectrometric measurements in the mass range of meteor smoke particles with mass-to-charge ratios up to m/z 2000, and measurements inside a polar mesospheric winter echo layer as detected by ground-based radar. Our ROMARA measurements took place on the Arctic island of Andøya, Norway, at around noon in April 2018 and represented an integral part of the polar mesospheric winter radar echo (PMWE) rocket campaign. During the rocket flight, ROMARA was operated in a measurement mode, offering maximum sensitivity and the ability to qualitatively detect total ion signatures even beyond its mass-resolving mass range. On this first ROMARA flight we were able to meet all of our objectives. We detected atmospheric species including positive atomic, molecular and cluster ions along with negative molecular ions up to about m/z 100. Above m/z 2000, ROMARA measured strong negative-ion signatures, which are likely due to negatively charged meteor smoke particles.

On the Nature of F‐Region Bottom‐Type Echoing Layer Over Gadanki

AbstractBottom‐type echoing layers observed from Gadanki are presented and analyzed. The analysis is based on observations made using a substantial database of the 30 MHz Gadanki Ionospheric Radar Interferometer (GIRI) during 2017–2019, collocated digisonde observations, and a few days of overlapping volume observations made using the GIRI and the 53 MHz Advanced Indian MST Radar (AIR) . The echoes commence well before the E‐ and F‐region sunsets and last as late as 23:00 Local Time. The echoing layers occur in the height range of 220–300 km with a thickness of 10–15 km and the Doppler spectra are narrow with spectral width confined to 10 m s−1. The echoing layers are very common during the entire observational period and do not show any noticeable seasonal dependence. The zonal velocities of the irregularities responsible for the radar echoes are close to zero irrespective of the height of the echoing region. The echoes are stronger at 30 MHz than at 53 MHz indicating strong Bragg scale dependence. The height of the echoing layer agrees very well with the height of the F‐region peak electron density (hmF2). Also, early commencement of the echoing layer is found to be associated with low hmF2 and corresponding high electron density (foF2). While the results indicate toward the wind‐driven interchange instability as their origin, the early onset of the echoing layer and its relationship with the background ionospheric parameters call for explanation. The results are discussed in the light of current understanding on the bottom‐type echoing layer.

Dynamically Unstable Strong Wind Shears Observed in the Polar Mesosphere Summer Echo Layer Associated With Geomagnetic Disturbances

AbstractWe report observations of dynamically unstable strong wind shear (Richardson number < 0.25) capable of inducing Kelvin‐Helmholtz instability in the polar mesospheric summer echoes (PMSE) layer (80–90 km) using very high frequency radar measurements in Kiruna (67.8°N, 20.4°E), Sweden, in 2006. The unstable strong wind shear can play an important role in producing PMSE by inducing turbulence and adiabatic cooling. We find that the strong shears take up 64% of the observed wind profiles and are frequently composed of systematically single‐shear/multishear (layer) structures, which gradually or abruptly vary in wind directions, so‐called wind shifts, through heights at intervals of 4–8 km. The strong shear rate normalized by PMSE counts has a good correlation (R = 0.7) in day‐to‐day variation with energetic electron (>30 keV) precipitations that were related to high‐speed solar wind streams. The observations of strong wind shear can be supported by satellite‐measured temperature modulations matching with the peaks of the first three high‐speed solar wind stream events. This study suggests that PMSE production is closely associated with the strong shear that is in turn linked to the effects of energetic electron precipitation.

A case of localized tracheobronchial relapsing polychondritis with positive matrilin-1 staining

BackgroundRelapsing polychondritis (RPC) is a rare progressive autoimmune disease characterized by inflammation in the cartilage of multiple organs. Tracheobronchial involvement appears in nearly half of RPC patients during the course of their disease and represents the main cause of death. Localized tracheobronchial RPC is much rarer, and the pathogenesis remains unclear. Matrilin-1 is a non-collagenous cartilage matrix protein and has been suggested to be a potent autoantigen that induces the airway disease of RPC in animal models. However, the expression of matrilin-1 in tracheobronchial tissue in human remains unclear. Therefore, we examined the expression of matrilin-1 in the tracheal and auricular tissues in a localized tracheobronchial RPC patient.Case presentationA 62-year-old man with systemic sclerosis presented with cough and dyspnea on exertion. The lung function test showed an expiratory flow limitation and chest computed tomography showed diffuse thickness from the trachea to the bronchiole. No other tests showed abnormal findings. To evaluate further, bronchoscopy was performed and endobronchial ultrasonography showed thickness in the fourth-marginal echo layer suggesting inflammation of the cartilage. However, the tracheal biopsy showed no specific findings. The subsequent surgical tracheal biopsies showed inflammatory cell infiltration with destruction of the cartilage. Neither auricular nor nasal deformity, except for a tracheobronchial lesion, was detected. Biopsy from the left auricular cartilage also did not show any inflammatory changes. Finally, we diagnosed the patient with localized tracheobronchial RPC. To address the hypothesis that autoimmunity against matrilin-1 is involved in the pathogenesis of localized tracheobronchial RPC, we evaluated the expression level of matrilin-1 in a tracheal and auricular specimen from this patient. Immunohistochemical staining with anti-matrilin-1 antibody showed matrilin-1 in the tracheal but not in the auricular cartilage.ConclusionsWe first demonstrated the expression of matrilin-1 in tracheal but not in auricular cartilage in a localized tracheobronchial RPC patient. This result supports the possibility that matrilin-1 is involved in the pathogenesis of localized tracheobronchial RPC. However, this is only one case report and further observations will be needed to confirm this result.

Height Variation of Gaps in 150‐km Echoes and Whole Atmosphere Community Climate Model Electron Densities Suggest Link to Upper Hybrid Resonance

AbstractRadar echoes from the daytime lower region near the magnetic equator, so‐called 150‐km echoes, have been puzzling researchers for decades. Neither the mechanisms that generate the enhanced backscatter at very high frequencies (typically 30–50 MHz), the sharp lower cutoff height, the intricate layering with multiple echo layers separated by narrow gaps, nor the modulation of the echoes by short‐period gravity waves is well understood. Here we focus on the diurnal variation of the echo layers—specifically, certain wide gaps in the vertical structure—which apparently descend in the morning, reach their lowest altitude near local noon, and ascend in the afternoon, sometimes described as necklace structure based on the appearance of the layers in range‐time‐intensity diagrams. Analyzing high‐resolution data obtained with the Jicamarca radar between 2005 and 2017, spanning more than one solar cycle, we find that (a) wide gaps and narrow lines occur in vertically stacked, systematically repeating pattern; (b) the gap heights vary with season and solar cycle; and (c) the gap heights can be associated with specific contours of plasma frequencies or electron densities. The last two findings are supported by simultaneous observations of VIPIR ionosonde reflection heights and by comparison of gap heights with electron density contours obtained with the WACCM‐X 2.0 global model. Finally, the wide gaps appear to coincide with the double resonance condition, where the upper hybrid frequency equals integer multiples of the electron gyrofrequency. This may explain why field‐aligned plasma irregularities are suppressed and enhanced radar backscatter is not observed inside the gaps.

Endoscopic resection of a giant symptomatic Brunner’s gland hamartoma of duodenal bulb

Brunner's gland hamartoma is a very rare benign tumor arising from the Brunner’s gland of duodenum and is usually asymptomatic, but may present with the symptom of duodenal obstruction or upper gastrointestinal bleeding due to ulceration from the tumor, requiring endoscopic or surgical resection. In our study, we report the case of a 57 year-old male who presented with pain over epigastrium, recurrent vomiting, black stool and dizziness with a lowering of hemoglobin up to 7.5 gm/dl. The blood transfusion was done to raise the hemoglobin. The upper gastrointestinal endoscopy revealed a giant submucosal polypoidal mass with a thick short stalk in duodenal bulb causing almost complete obstruction of the lumen of duodenum and there was a superficial ulceration on the under-surface of the mass. The endoscopic ultrasound revealed a submucosal lesion arising from the echo layer three. The computed tomography of abdomen showed that the polypoidal mass was confined to the duodenal lumen with no significant lumphadenopathy and normal biliary and pancreas. The endoscopic polypectomy was attempted, but the lesion was too large to grab the polyp as a whole with the conventional snare. Hence, the repeated partial snare polypectomies were done, followed by submucosal dissection to ensure the complete removal of the mass. There were no complications after the procedure. The histopathology examination of the duodenal mass confirmed the diagnosis of Brunner’s gland hamartoma and showed the presence of Helicobacter pylori as well. The endoscopic treatment of giant Brunner’s gland hamartoma avoided the need of unnecessary more invasive surgical procedure.

2769 Large Gastric Gastrointestinal Stromal Tumor With Spontaneous Rupture of Necrotic Fluid Collection

INTRODUCTION: Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumor of the gastrointestinal tract. Fluid collection within GISTs is very rare with only several case reports documented. We present the first case of spontaneous rupture from a large gastric GIST with necrotic fluid collection which has been documented on endoscopic exam. CASE DESCRIPTION/METHODS: A 91 year-old Caucasian female with a 3 month history of weight loss and progressive dysphagia to solids presented for evaluation. She was afebrile and hemodynamically stable with mild tachycardia. Initial labs revealed mild leukocytosis and low protein/albumin. Computer tomography demonstrated large 12 × 11 cm gastric mass with air-fluid level. Follow-up diagnostic esophagogastroduodenoscopy (EGD) showed a large fundic mass with two large cratered ulcerations with bridging mass in the proximal stomach with unremarkable histology on biopsy. Follow-up EGD with endoscopic ultrasound (EUS) demonstrated similar visualization with now small collection of purulent fluid though no fistula was appreciated. On EUS there was a larger heterogeneous hypoechoic mass bridging across all echo layers and a fluid echogenicity without doppler flow contained within the mass. Fine needle aspiration showed spindle cell neoplasm (CD117 +, DOG1 +) compatible with GIST. Given comorbidity and advanced age, she was not considered a surgical candidate. After starting Imatinib, she was offered therapeutic EGD was for possible decompression of the fluid collection within the tumor, to relieve mass effect for palliation. On visual exam there was again evidence of more purulent material that was extruding from a small opening in the center of the mass. The endoscope was advanced into the small opening and revealed a large fluid filled cavity within the mass. After copious irrigation with suction the majority of the cystic fluid was removed and two plastic double pigtail stents were placed to allow full decompression of the cystic cavity. On follow-up exam, she reported improvement of her pain. DISCUSSION: GIST are most often found in the stomach but overall account for 3% of all gastric malignancies. The initial presentation is often asymptomatic but there are many cases of highly variable symptomatic presentations of larger GIST. GIST with cystic changes are considered rare, with only 11 cases reported to date. This case is the first documentation of a cystic GIST that spontaneously ruptured, forming a fistulous tract between the cavity and the stomach.

Ligation assisted endoscopic mucosal resection of neuroendocrine tumor of duodenal bulb: a case report with a follow up of 24 months

Duodenal neuroendocrine tumor (NET) is a rare solitary lesion arising from the mucosa and submucosa of the duodenum, which is found incidentally during upper gastrointestinal endoscopy. Eendoscopic Mucosal Resection (EMR) has been the commonly used endoscopic procedure for duodenal carcinoid tumors, but the conventional EMR done to resect duodenal NET s is likely to have positive vertical margins. However, the ligation assisted EMR has recently been shown to be a promising technique for the treatment of duodenal NET that can have a negative free margin. In our study, we present a patient of 51-year-old male, who presented with pain over epigastrium and upper gastrointestinal endoscopy revealed a small submucosal lesion of 10 mm in the duodenal bulb. The endoscopic ultrasound showed the lesion arising from the echo layer three. The biopsy was taken which showed the duodenal NET. The computed tomography of abdomen did not show any evidence of distant metastasis. The EMR of duodenal NET was done by band ligation technique. The biopsy from the resected duodenal lesion confirmed the duodenal NET with the margin free of the tumor. The patient was followed at 6, 12, 18 and 24 months. During the follow up visits, the repeat upper gastrointestinal endoscopy did not show recurrence of the lesion and there was no any evidence of distant metastasis either. Ligation assisted EMR is an acceptable treatment in the hands of expert for small duodenal NET without the evidence of metastasis and can ensure the complete removal of the lesion with vertical free margin.

EISCAT Observation of Wave‐Like Fluctuations in Vertical Velocity of Polar Mesospheric Summer Echoes Associated With a Geomagnetic Disturbance

AbstractBy analyzing a data set from the European Incoherent SCATter (EISCAT) Very High Frequency (VHF) radar at Tromsø, we find that both radar reflectivity and upward ion velocity in a polar mesospheric summer echo (PMSE) layer simultaneously increased at the commencement of a local geomagnetic disturbance, which occurred at midnight on 9 July 2013. The onset of the upward velocity was followed by periodic repetition of ~5 min during the initial 30‐min stage, and then at later stage the vertical velocity oscillated with ~7‐ and ~20‐min periodicities at 85‐ to 90‐km altitudes. The ~5‐min periodicity is close to the buoyancy period, and the ~7‐ and ~20 min periodicities are consistent with gravity waves, thus suggesting that gravity waves can be generated by the effects of the geomagnetic disturbance. On the other hand, the variation of PMSE intensity (85–90 km) was in phase with fluctuations of electron densities (90–110 km) with ~12‐ and ~13‐min periodicities at the initial and later stages, respectively. The initial creation of PMSE can be attributed to both the sudden onset of particle precipitation and ice particles produced by adiabatic cooling during the rapid updraft, as detected by large upward velocity. Our periodogram analysis suggests that variations of PMSE intensity seem to follow the same periods with E region electron density, which is moduled by energetic electron precipitation, while vertical velocity oscillates at atmospheric gravity wave periods.

First Dual‐Frequency Radar Observations of 150‐km Echoes From Gadanki and Implications

AbstractWe present the first dual‐frequency overlapping volume radar observations of daytime 150‐km echoes made at 30 and 53 MHz from Gadanki, India. We show remarkably different responses of the 150‐km echoing layers including the spectral characteristics of the echoes at 30 and 53 MHz. Results show that while the echoes in general are remarkably stronger with narrower spectral width at 30 MHz than that of 53 MHz the relationship between radar cross sections at the two frequencies varies depending on the echoing layer. We also show distinctly different spectral broadening in different echoing regions observed by the 53‐MHz radar, which is missing in the 30‐MHz radar observations. These new observations indicate involvement of naturally enhanced incoherent scattering as well as scattering from enhanced electron density fluctuations of plasma instability origin and hence are of utmost importance in understanding the origin of the puzzling 150‐km echoing phenomenon.

On the Performance of the Range Imaging Technique Estimated Using Unmanned Aerial Vehicles During the ShUREX 2015 Campaign

For the first time, the performance of the range imaging technique of the very high frequency band middle and upper atmosphere (MU) radar (Shigaraki observatory, Japan), when using frequency diversity, is assessed. This is done by the detection of unmanned aerial vehicles (UAVs) operated near the radar during the Shigaraki UAV radar experiment campaign, carried out from June 1, 2015 to June 14, 2015. During this campaign devoted to the measurements of fine-scale turbulence and stability in the lower troposphere using the turbulence sensors on the DataHawk UAV and the MU radar, the detection of the small UAV by the MU radar provided an excellent opportunity for taking stock of the range imaging technique in the presence of a single hard target. It was found that range imaging reproduces a faithful image of the aircraft position and its displacements with an excellent accuracy (of the order of ~10 m), giving extra credence to the thin echo layers and their vertical displacements generally observed from the range imaging technique in stably stratified conditions.

On the linkage of daytime 150 km echoes and abnormal intermediate layer traces over Sanya

AbstractThe daytime 150 km echoes, which are associated with the upper E region field‐aligned irregularities, have been observed around the equatorial electrojet region but never before at magnetic latitudes near the northern anomaly crest region. We present first results of daytime 150 km echo over Sanya, China, a station located far away from the dip equator in the Northern Hemisphere. A layer of weak radar echoes with spectral width less than 10 m s−1 was seen in the height range from 145 km at 12:15 LT to 152 km at 13:45 LT on 21 July 2010. The interesting aspect is that the rare observation of daytime 150 km echoes with the small Sanya VHF radar was preceded by the occurrence of an unusual intermediate layer, which is identified as abnormal traces at the upper E region in corresponding ionograms. The abnormal intermediate layer associated with possible gravity wave activity (that implicates the presence of upper E region density gradients) could make a significant contribution to the growth of irregularities responsible for the rarely detected daytime 150 km echoes over Sanya.

Endoscopic Ultrasound for Diagnosis and Surveillance of Gastrointestinal Stromal Tumors in an 11‐Year‐Old Child

Endoscopic Ultrasound for Diagnosis and Surveillance of Gastrointestinal Stromal Tumors in an 11‐Year‐Old Child

Utilization of Bedside Urogenital Ultrasound in an Austere Combat Setting: Enterovesicular Fistula Case Report

The role of bedside ultrasound by physicians with advanced ultrasound training, such as emergency medicine providers, has been clearly established in the austere setting of combat medicine. This highly mobile, noninvasive, and versatile imaging modality has a role in evaluating battle- and nonbattle-related presentations. This case report describes a U.S. Marine reporting to an austere medical facility with the chief complaint of abdominal pain. An ultrasound of the patient's urinary tract revealed abnormalities that suggested right bladder wall thickening and an echo dense layer of sediment as the potential source of his discomfort. These findings supported patient transfer to a higher echelon of care. Further diagnostic testing revealed Crohn's disease with an associated enterovesicular fistula.

Lymphangioma of Esophagus Presenting with Dysphagia: A Case Report

Purpose: Lymphangioma of the esophagus is a benign vascular tumor that rarely occurs in the upper GI tract. We report a rare case of lymphangioma of the esophagus and our experience with endoscopic resection of this lesion. A 61 year old Hispanic man with history of dysphagia was referred for evaluation of a polypoid lesion in the mid-esophagus. An EGD done by his gastroenterologist a year earlier demonstrated a submucosal polypoid lesion in the mid esophagus. The patient was placed on a PPI and was referred for an EUS. EGD showed a 1 cm submucosal lesion at 25 cm from incisors. It was round, with normal appearing overlying mucosa and was easily compressed with cold forceps. EUS demonstrated a 13 × 5 mm anechoic lesion arising from the second echo layer corresponding to submucosal space. Next, using cold standard forceps, multiple biopsies were taken in a “bite and bite” tunneling method with obliteration of the lesion. Histology showed cavernous lymphangioma of the esophagus. His dysphagia improved after removal of the lesion. Discussion: Lymphangiomas are benign lesions that arise from the cystic dilatation of hamartomas in deep lymphatic tissue and are rarely found in the GI tract (1%). The esophagus is the most unusual location for this lesion. The diagnosis of lymphagioma is usually made on histopathology. The masses are composed of enlarged channels lined by lymphatic endothelial cells surrounded by a loose myxoid stroma. On gross examination, they are usually pale and smooth, with a multicystic cut surface and a clear yellowish fluid exudate. The common tools to establish the diagnosis are esophagram and EGD. Lymphangiomas appear as a translucent, yellowish, easily compressible mass lesions that are < 5 mm. Standard biopsies are often normal as the lesions are submucosal. EUS may the most useful tool for distinguishing a lymphangioma from other submucosal tumors because it aids in differentiating submucosal lesions from lesions that arise from the muscular layers of the esophagus. The treatment of esophageal lymphangioma is conservative in asymptomatic patients. For symptomatic pateints, response to surgical or endoscopic removal of these tumors is excellent. However, a large tumor with symptoms or a lesion suspicious for malignancy requires surgical resection. Determining the extent of the tumor through the esophageal wall may be difficult during resection as the lymphangioma is soft and compressible. Conclusion: Lymphangioma of the esophagus is a rare submucosal tumor, generally small and benign in nature. Endoscopic ultrasound is an excellent tool for diagnosis of these lesions. Our experience reaffirms that endoscopic excision of such lesions is safe and appears to be without major complications.

Descending ion layer property in the Gadanki radar observations of 150 km echoes and its implication to the echoing phenomenon

[1] Gadanki radar observations of the daytime 150 km echoes displaying descending features, resembling the descending ion layer behavior, are presented. The descending pattern is intriguing since it indicates the possible role of density gradient associated with the ion layer in generating the irregularities responsible for 150 km radar echoes, not envisioned before. Unusually strong SNR and narrow spectral features of these echoes clearly indicate the role of sharp density gradients in the echoing process. Given the fact that Gadanki is located at magnetically low latitude, it is argued that these descending echoing layers are produced by interchange instability on the gradient of daytime descending ion layer formed by meridional wind shear associated with tidal/gravity waves quite similar to that observed during nighttime. The observations reported here are first of its kind illustrating the role of density gradient layers and are important in furthering our understanding on the puzzling 150 km echoing phenomenon.

On the characteristics of 150-km echoes observed in the Brazilian longitude sector by the 30 MHz São Luís radar

Abstract. We present long-overdue details about the intensity and spectral characteristics of 150-km echoes observed by the São Luís radar in Brazil. The São Luís observations show that the echoes usually come from multiple scattering layers that descend in altitude before local noon, and ascend during afternoon hours, similar to what has been found in observations made in other longitude sectors. The layers are usually 3–5 km thick and located, mostly, between 130 and 170 km altitude. The measurements also show variations in echo intensity that are similar to observations made at other equatorial and off-equatorial sites. Analysis of observations made during 2008 shows significant (&gt;37%) monthly occurrence rates for every month. Reduced occurrence rates were observed around March Equinox. We associate this reduction in occurrence rate, however, to a non-geophysical factor. An increase in the daytime sky noise in the months around March Equinox causes a decrease in the signal-to-noise ratio (SNR) of the echoes, which makes them less distinguishable in our analysis. A higher occurrence of weaker echoes around March Equinox was confirmed by an statistical analysis of the seasonal variation of echo intensities. Strong, long-lasting and, therefore, more noticeable echoing layers, however, were observed between June and early September compared to other months in 2008. Spectral analyses show that most of the echoes have negative mean Doppler shifts indicating upward velocities. The echoes also have narrow spectral widths of only a few m s−1. Finally, we also found that the mean Doppler shift of the observed echoes can vary noticeably with altitude at times. Using spaced antenna measurements we show that this is caused by the wide field-of-view of the radar and the spatial distribution of the scatterers within the radar beam.

Layers of insect echoes near a thunderstorm and implications for the interpretation of radar data in terms of airflow

AbstractInsects can serve as useful radar targets for determining aspects of the structure and kinematics of the atmosphere, but it is necessary sometimes to know more about insect behaviour in order to have confidence in the meteorological interpretations. A variety of meteorological radars situated at Chilbolton in southern England have been used to investigate the nature of multiple shallow clear‐air echo layers that were detected at heights between 1.0 and 2.5 km in the vicinity of an elevated daytime thunderstorm (mesoscale convective system). Multi‐wavelength and polarization measurements were used to confirm that the layers were due in large part to insects. The layers were within potentially warm air near the top of a cold undercurrent of surface air. The convective updraught of the thunderstorm was fed by air from just above the cold undercurrent. Some of the insect layers were within air destined to ascend into the storm's convective updraught and some were within undercurrent air that was forced to ascend only temporarily as the storm approached. Initially the layer echoes ascended with the airflow but then, close to the storm, their intensity weakened despite continuing updraughts, mainly as a result of the insects dropping downwards. Far ahead of the storm the insects showed a strong preference to remain within their individual shallow layers but, even close to the storm, where they started dropping out, insects still retained a preference to be within these layers. As a result, some layers continued to be discernible as they followed the ascending airflow towards the storm, thereby continuing to serve as useful meteorological tracers of the perturbed flow in the vicinity of the thunderstorm. Copyright © 2011 Royal Meteorological Society