Prenoon Hours Research Articles

Climatology of TEC Longitudinal Difference in Middle Latitudes of East Asia

In this paper, a statistical analysis of the diurnal, seasonal and solar cycle variation in the TEC longitudinal difference in midlatitudes of East Asia is presented using CODE GIMs data in 2015–2019. Moreover, the empirical neutral wind model HWM-14 and geomagnetic field model IGRF-2020 were employed to analyze the influence of geomagnetic configuration-neutral wind mechanism on the TEC longitudinal difference, and the F2 layer peak electron density (NmF2) data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) were also used to study the role of local electron density in the TEC longitudinal difference. For the high solar activity year, the results show that east-west TEC longitudinal difference index Re/w is negative in the noon and positive at evening-night. Moreover, the longitudinal difference of daytime TEC is most evident in summer, less in autumn and least in spring and winter, while the nighttime difference is most obvious in equinox, followed by summer and winter during nighttime. The model simulation shows that the TEC longitude difference around noon is mainly caused by the zonal wind-declination mechanism, and a 4-h time delay seems to be an optimal result for the vertical drift velocity to cause the longitudinal TEC difference during pre-noon hours. At night, the uplifting electron flux, which is a product of local electron density and vertical drift velocity, shows a good correlation with Re/w, indicating that the local electron density is also an important factor affecting the TEC longitudinal difference during the nighttime. Moreover, there was about a 3-h time delay between the TEC longitudinal variations and the uplifting electron flux at night. For the low solar activity years, the western TEC is greater than eastern TEC during most of the year except in the summer nighttime. The TEC diurnal variation in the east and west suggested that the nighttime Re/w should be related to other physical process, such as the midlatitude summer nighttime anomaly (MSNA) in the east and the ionospheric nighttime enhancement (INE). The current study provides evidence for the longitudinal difference of NmF2 in East Asian midlatitudes and geomagnetic configuration-neutral wind mechanism proposed in previous studies and finds some new features which need further studying to improve our current understanding of ionospheric longitudinal difference in the low solar activity years. The results provide new insight into TEC longitudinal variations at midlatitudes, and they can contribute to understanding the ionosphere-thermosphere coupling system.

On the possible role of zonal dynamics in the formation and evolution of F3 layers over equator

In the present study, occurrences of F3 layer over Thiruvananthapuram (8.5°N; 77°E; dip latitude ~0.5°N), a dip equatorial station in India have been investigated using ionosonde data for the years 2004–2007. The F3 layers appearing in the ionograms during the pre noon hours only have been included in the analysis. The result indicates that a weak EIA resulting in low ionospheric height and high ionization density prevails before the occurrence of F3 layer and serves as an essential condition for its occurrence. The relative Slant Total Electron Content (rSTEC) measured using collocated ground based coherent low earth orbiting (LEO) radio beacon receiver has also been used along with electron densities measured by CHAMP satellite for the year 2006 and 2007 to illustrate this difference in the evolution of Equatorial Ionization Anomaly (EIA) on F3 and non F3 days. A new mechanism for F3 generation has been proposed. It has been shown that the coupling of the thermospheric zonal wind jet over equator and enhanced ionospheric density at lower heights over Indian longitude can account for the generation of F3 layer through ion-drag. The vertical wind associated with the thermospheric heating resulting from ion-drag causes the generation of an additional eastward field which, along with the prevailing F-region electric field, leads to the upward excursion of the F3 layer.

Variations in Electron Content Ratio and Semi-thickness Ratio during LSA and MSA periods and some Cyclone Genesis Periods using COSMIC satellite observations

In this study for the first time, COSMIC satellite data have been used to deduce values of ionospheric Electron Content Ratio (ECR) and Semi-thickness Ratio (Rtb) for Low Solar Activity (LSA) (2008) and Moderate Solar Activity (MSA) (2012) periods over the Indian low-latitude (15–30°N) region with 80–95°E longitude. These two ratios provide sensitive information about bottom and topside ionosphere for different geophysical conditions. Extraction of suspected patterns and discrepancies unfold that the deviations between ECR and Rtb values during LSA period are comparatively higher than that of MSA period when the diurnal variability in these two parameters is flatter along with the diurnal-dips during pre-noon hours. The correlative relationship of ECR exhibits low association with NmF2 and anti-correlation with HmF2, whereas its correlation with Rtb is extremely high. During Cyclone Genesis Period (CGP) strong dips in ECR and Rtb values with respect to pre and post CGP occurred which helps to take decisive conclusion about the ionospheric variations to be dominant through getting relatively higher Ne concentration in the bottom side part of the ionosphere.

Characterizing the diurnal patterns of errors in the prediction of evapotranspiration by several land‐surface models: An NACP analysis

AbstractLand‐surface models use different formulations of stomatal conductance and plant hydraulics, and it is unclear which type of model best matches the observed surface‐atmosphere water flux. We use the North American Carbon Program data set of latent heat flux (LE) measurements from 25 sites and predictions from 9 models to evaluate models' ability to resolve subdaily dynamics of transpiration. Despite overall good forecast at the seasonal scale, the models have difficulty resolving the dynamics of intradaily hysteresis. The majority of models tend to underestimate LE in the prenoon hours and overestimate in the evening. We hypothesize that this is a result of unresolved afternoon stomatal closure due to hydrodynamic stresses. Although no model or stomata parameterization was consistently best or worst in terms of ability to predict LE, errors in model‐simulated LE were consistently largest and most variable when soil moisture was moderate and vapor pressure deficit was moderate to limiting. Nearly all models demonstrate a tendency to underestimate the degree of maximum hysteresis which, across all sites studied, is most pronounced during moisture‐limited conditions. These diurnal error patterns are consistent with models' diminished ability to accurately simulate the natural hysteresis of transpiration. We propose that the lack of representation of plant hydrodynamics is, in part, responsible for these error patterns.

A global comparative study on the ionospheric measurements between COSMIC radio occultation technique and IRI model

[1] We compare ionospheric parameters including total electron content (TEC), peak density, and height of the F2 layer (NmF2 and hmF2) between FORMOSAT-3/COSMIC (F3/C) GPS radio occultation (RO) technique retrieved and International Reference Ionosphere (IRI-2001) model predicted during different seasons in a low solar activity (LSA) year 2007. The comparison of topside TEC (tTEC, obtained by integrating electron density from hmF2 to 800 km) between IRI and F3/C shows that the IRI overestimates tTEC during both equinox seasons at around ±15° magnetic latitudes during daytime, especially in March equinox while underestimation of tTEC predicted by IRI is a dominant feature for both solstices. Further, a common finding is that the IRI overestimates tTEC from evening to prenoon hours irrespective of season at around ±20° magnetic latitudes, which is most likely due to the underestimation of hmF2 (by around 30–40 km), a key parameter on which the build of electron density profile depends in the model and inaccurate representation of the real profile by the topside electron density profiler model in IRI. The global distributions and seasonal variations of NmF2 show clear semiannual and annual asymmetry features during daytime and such features also reflected in IRI predicted peak densities with few exceptions. This high degree of agreement between tTEC comparison and the characteristic features of NmF2 global distributions indicates that the majority of contribution for tTEC has come from the F2 region. Further, it is also presented the global distributions of topside vertical scale heights (VSH) computed using electron density profiles retrieved from F3/C and predicted by IRI model during different seasons in year 2007. An important finding is that the topside VSH of F3/C profile data is meticulously following the geomagnetic equator during daytime irrespective of season and tends to increase toward higher latitudes. An appreciable latitudinal difference is found in the season averaged scale heights that derived with F3/C data during daytime while completely opposite results are found for IRI predicted scale heights. The discrepancies of topside VSH between the F3/C derived and predicted by IRI indicating that the shape of the topside electron density profile in the IRI model should desperately be revised accordingly such that it more closely resembles the real situation.

High-latitude plasma convection during Northward IMF as derived from in-situ magnetospheric Cluster EDI measurements

Abstract. In this study, we investigate statistical, systematic variations of the high-latitude convection cell structure during northward IMF. Using 1-min-averages of Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for six and a half years (February 2001 till July 2007), and mapping the spatially distributed measurements to a common reference plane at ionospheric level in a magnetic latitude/MLT grid, we obtained regular drift patterns according to the various IMF conditions. We focus on the particular conditions during northward IMF, where lobe cells at magnetic latitudes >80° with opposite (sunward) convection over the central polar cap are a permanent feature in addition to the main convection cells at lower latitudes. They are due to reconnection processes at the magnetopause boundary poleward of the cusp regions. Mapped EDI data have a particular good coverage within the central part of the polar cap, so that these patterns and their dependence on various solar wind conditions are well verified in a statistical sense. On average, 4-cell convection pattern are shown as regular structures during periods of nearly northward IMF with the tendency of a small shift toward negative clock angles. The positions of these high-latitude convection foci are within 79° to 85° magnetic latitude and 09:00–15:00 MLT. The MLT positions are approximately symmetric ±2 h about 11:30 MLT, i.e. slightly offset from midday toward prenoon hours, while the maximum (minimum) potential of the high-latitude cells is at higher magnetic latitudes near their maximum potential difference at ≈−10° to −15° clock angle for the North (South) Hemisphere. With increasing clock angle distances from ≈IMFBz+, a gradual transition occurs from the 4-cell pattern via a 3-cell to the common 2-cell convection pattern, in the course of which one of the medium-scale high-latitude dayside cells diminishes and disappears while the other intensifies and merges with the opposite main cell of the same polarity to form the large "round-shaped" convection cell when approaching a well-known IMFBy-dominated configuration. Opposite scenarios with interchanged roles of the respective cells occur for the opposite turning of the clock angle and at the Southern Hemisphere. The high-latitude dayside cells become more pronounced with increasing magnitude of the IMF vector.

Ionospheric precursors observed at low latitudes around the time of koyna earthquake

On December 11, 1967 at 05:21 LT, an immense earthquake of magnitude 6.7 struck Koyna, the Indian province of Maharashtra. Its epicenter was located at geographic latitude 17.37°N and longitude 73.75°E with depth of about 3 km. Ground based measurements show variation in the critical frequency of ionospheric F2 layer (foF2) before and after the shock. In the present study the behavior of F2-region of ionosphere has been examined over the equatorial and low latitudinal region ionosphere during the month of December 1967 around the time of Koyna earthquake. For this purpose, the ionospheric data collected with the help of ground-based ionosondes installed at Hyderabad (located close to the earthquake epicenter) Ahmedabad, Trichirapulli, Kodaikanal and Trivendrum have been utilized. The upper and lower bound of Interquartile range (IRQ) are constructed to monitor the variations in foF2 other than day-to-day and diurnal pattern for finding the seismo-ionospheric precursors. Some anomalous electron density variations are observed between post midnight hours to local pre-noon hours at each station. These anomalies are strongly time dependent and appeared a couple of days before the main shock. The period considered in this study comes under the quiet geomagnetic conditions. Hence, the observed anomalies (which are more than the usual day-to-day variability) over all stations are likely to be associated with this imminent earthquake. The possible mechanism to explain these anomalies is the effect of seismogenic electric field generated just above the surface of earth within the earthquake preparation zone well before the earthquake due to emission of radioactive particles and then propagated upward, which perturbs the F-region ionosphere.

A study of the relationship among temperatures of surface features and its application in remote sensing study of Lut desert

Physical characteristics of different features in desert is a reflection of severe thermal and climatic conditions. In this paper, diurnal surface temperature patterns of important surface features in Lut Desert were studied and the relationship among different surfaces analyzed. Diurnal trend in surface temperature of surface types, marl, dark sand, light sand, salt-affected soil, soul at 10 cm depth, as well as dry and wet air temperature within 15 days were recorded in 2 hour intervals in the margin of Lut yardangs while correlations among these surface features and its significance level were investigated. The knowledge of diurnal temperature pattern and calculation of correlation among features can lead us to the understanding of the behavioral pattern and the trend of surfaces. The knowledge of behavioral pattern of correlation coefficients during different hours of the day provides the researchers the ability to produce optimal models of thermal characteristics and to predict them. Additionally, thermal data of different sensor systems along with their capability in the study of surface features in Lut Desert was evaluated. The results of thermal and inter-feature correlation analysis reveal a similar trend (at 8 AM and 4 PM) among various feature types. The correlation coefficient of different surfaces shows the highest value at 6 AM and the lowest at 8 PM. The correlation coefficient between sand and marl with grey sand and soil shows a non-linear trend at pre-noon hours while a linear and similar trend in the afternoon. Generally speaking, the correlation coefficient between surfaces at pre-noon hours as compared to afternoon hours is completely non-linear and does not reveal any specific pattern. It seems that TIR data acquired at 10 AM is the best choice in the study of Lut Desert and hence ETM + and TM data can be used.

Complex study of the auroral arc dynamics and ionospheric plasma convection in prenoon hours

The dynamics of auroral arcs, observed in the prenoon sector during the 2-h period, has been studied in the context of ionospheric convection. The appearance of an isolated arc, the poleward drift velocity of which pronouncedly exceeded the plasma drift velocity, accompanied the IMF impulse and could result from the Alfven resonance oscillations of the magnetosphere. Arcs that appeared after the northward turning of the IMF vertical component drifted poleward at a velocity close to the convection velocity. The mechanism of arc generation is related to the flute instability which develops in the region of the large-scale field-aligned current. Flute instability indications are found out in the POLAR satellite data. The study confirms the previously proposed classification criterion for dayside arcs with the source on closed field lines, based on the character of arc drift as compared to convection.

Statistical analysis of compressional Pc3–4 pulsations observed by AMPTE CCE at L = 2–3 in the dayside magnetosphere

Few spacecraft observations of Pc3–4 (7–100 mHz) pulsations at L < 3 have been reported, although ground observations of the pulsations in the same L range are routine. In particular, there are no systematic spacecraft observations of compressional pulsations expected at the time of low‐latitude ground Pc3–4 pulsations that exhibit a constant frequency over a range of L. These pulsations have been attributed to fast mode waves trapped in the plasmasphere (referred to as plasmaspheric cavity mode waves) or to evanescent waves that exist inward of the turning point for fast mode waves propagating from the outer magnetosphere. We studied the properties of compressional Pc3–4 pulsations at L < 3 using magnetic field data simultaneously acquired by the Active Magnetospheric Particle Tracer Explorers Charge Composition Explorer (AMPTE CCE) and at the Kakioka ground station (L = 1.25) over a 2‐year period from 1985 to 1986. From time intervals when the satellite was on the dayside and between L = 2 and L = 3, we identified 63 cases of magnetospheric compressional (bz) Pc3–4 pulsations with or without an accompanying perturbation in the radial (bx) component, depending on the latitude of the satellite. The pulsations were observed primarily when AMPTE CCE was at prenoon hours (magnetic local time (MLT) = 0800–1200), and they were often accompanied by nearly identical magnetic pulsations at Kakioka. In an attempt to construct the spatial mode structure of the compressional pulsations, we have examined the relationship between the bx and bz components and also between the bz (or bx) component and the horizontal H (north–south) component at Kakioka. We find that the phase and amplitude relationship between bx and bz is consistent with waves standing in the meridian plane. The ground‐satellite cross phase is clustered near the values expected for radially standing or evanescent waves but also exhibits considerable deviations from the expected values. Although we have demonstrated that compressional Pc3–4 pulsations exist in the low‐L magnetosphere and that they give rise to pulsations on the ground, we conclude that further study is required to distinguish between the cavity and evanescent modes.

Horizontal meridional thermospheric winds over King George Island, Antarctica, during the June 1991 Geomagnetic storm

Abstract Diurnal variations of the magnetic meridional component of the thermospheric neutral wind have been derived from both a servo model based algorithm with ionosonde data input, and the HWM-90 empirical wind model for the 4–6 and 11–13 June 1991 geomagnetic storm at King George Island (62.2°S, 58.8°W). While the HWM-90 winds are predominantly equatorward, the servo model winds are predominantly poleward during the storm, with especially strong poleward winds in the pre-noon hours. Such strong poleward winds are not expected to occur during a major storm at such a low geomagnetic latitude (51.4°S), which is equatorward of direct ion drag forcing by magnetospheric convection electric fields. We speculate that this atypical thermospheric wind response may be associated with particle heating in the South Atlantic Anomaly.

Equatorial Counter-Electrojet and Magnetic Pulsations.

The signal amplitudes in the Hx component of magnetic pulsations undergo significant enhancement at the dip equator during intervals of Equatorial Electrojet (EEJ), the enhancement attaining a peak value during prenoon hours. On the other hand, it is shown in this study, that the enhancement peak which occurs during prenoon hours on EEJ days shifts towards noon hours on major counter electrojet (CEJ) days. The observed shift of the peak towards noon hours is interpreted to indicate corresponding change in the diurnal variation of ionospheric conductivity during the CEJ days.

Some modelling studies of the equatorial ionosphere using the Sheffield University Plasmasphere Ionosphere Model

The Sheffield University Plasmasphere Ionosphere Model (SUPIM) has been used to study the importance of diffusion, vertical E × B drift, and neutral wind on the generation and modulation of the equatorial plasma fountain and the equatorial anomaly of the Earth's ionosphere. The study has been carried out for the longitude of Jicamarca under magnetically quiet equinoctial conditions at medium solar activity. The model results indicate that the behaviour of the fountain closely follows the variation of the F region vertical E × B drift. During daytime the fountain rises to a maximum altitude of about 800 km at the equator and covers magnetic latitudes of about ±30°. At regions outside the fountain plasma flows towards the equator and this leads to the formation of an additional layer during the prenoon hours between latitudes ±10°; we call this layer the G layer. The maximum plasma concentration of the G-layer can be greater than that of the F layer for a short period of time just before noon. In the evening, soon after the drift turns downward, the fountain becomes a reverse fountain with supply of ionization from the region outside the fountain. The neutral wind modulates and introduces latitudinal asymmetries into both the fountain and anomaly.

Equatorial plasma fountain and its effects: Possibility of an additional layer

The importance of diffusion, perpendicular electrodynamic drift, and neutral wind on the generation and modulation of the equatorial plasma fountain of the Earth's ionosphere is studied using the Sheffield University plasmasphere‐ionosphere model for the ionosphere above Jicamarca under magnetically quiet equinoctial conditions at medium solar activity. The effects of the fountain, which include the equatorial anomaly, are also investigated. As expected, the F region electrodynamic (E×B) drift generates the plasma fountain and the anomaly, which are symmetric with respect to the magnetic equator. The neutral wind introduces asymmetries, with larger plasma flow (toward the hemisphere of stronger poleward wind) and stronger anomaly crest occurring in opposite hemispheres. During daytime, when the drift is upward, the fountain rises to about 800 km altitude at the equator and covers about ±30° magnetic latitude; outside the reach of the fountain, plasma flows toward the equator from both hemispheres. This convergence of plasma leads to the formation of an additional layer (called the G layer) within ±10° of the magnetic equator during the prenoon hours when the drift is large. At the magnetic equator, the maximum plasma concentration of the G layer can be greater than that of the F layer for a short period of time just before noon and when the drift starts to decrease. In the evening, soon after the drift turns downward, the fountain becomes a reverse fountain with supply of ionization from both hemispheres from regions outside the fountain. The reverse fountain acts as the main source for the nighttime increase in ionization at equatorial anomaly latitudes, with some contribution from the prereversal strengthening of the forward fountain. The importance of the prereversal strengthening of the forward fountain, which rises to about 1000 km altitude at the equator, and the following reverse fountain on the generation and propagation of plasma bubbles and spread F irregularities is discussed. It is also shown that the equatorial anomaly in the vertical ionospheric electron content need not be as pronounced as the interpretation of the observations suggests.

Observations of 50-MHz type-II coherent echoes from within the polar cap

Abstract. 50-MHz type-II coherent echoes at geometrical aspect angles of 11.5° have been observed in the northern polar cap during pre-noon hours. The echoes had an unusually large Doppler width of 1200-1400 m s-1 and were well correlated with strong magnetic disturbances in the range 500-1000 nT. The dependence of intensity, spectral width and skewness versus radial velocity were similar to those known from previous experiments at lower latitudes and at small aspect angles. It is concluded that echo onset was due to the combination of several factors, including a highly conducting ionosphere, the presence of a very intense electric field, and strong radar wave refraction.

Observations of 50-MHz type-II coherent echoes from within the polar cap

50-MHz type-II coherent echoes at geometrical aspect angles of 11.5° have been observed in the northern polar cap during pre-noon hours. The echoes had an unusually large Doppler width of 1200-1400 m s-1 and were well correlated with strong magnetic disturbances in the range 500-1000 nT. The dependence of intensity, spectral width and skewness versus radial velocity were similar to those known from previous experiments at lower latitudes and at small aspect angles. It is concluded that echo onset was due to the combination of several factors, including a highly conducting ionosphere, the presence of a very intense electric field, and strong radar wave refraction.

A statistical study of Pc 3–5 pulsations observed by the AMPTE/CCE Magnetic Fields Experiment, 1. Occurrence distributions

Three‐component dynamic spectrograms (0–80 mHz) of AMPTE/CCE magnetic field data from August 24, 1984, through December 7, 1985, have been used to survey ULF pulsation activity occurring from L = 5 to 9 in the equatorial magnetosphere (±16° magnetic latitude) at all local times. The data were scanned visually, and each half‐hour interval was categorized by spectral type, approximate polarization, spectral intensity, and spacecraft location to produce a data base representing 7231 hours of observations. Coherent pulsations are divided into nine categories which fall into four basic classes: (1) harmonic toroidal resonances (17.9% of the data), (2) fundamental mode toroidal resonances (11.0%), (3) radially polarized pulsations (5.2%), and (4) compressional low‐frequency pulsations (10.6%). Classes (1) and (2) are not mutually exclusive. Intervals devoid of coherent pulsations are divided into five levels according to noise intensity and account for 56.8% of the observations. Uncategorized events represented 4.2% of the data. The spatial occurrence distributions of each pulsation category and the latitude distribution of selected categories have been examined. The basic conclusions of the study are as follows: (1) Harmonic toroidal resonances are found to be the dominant coherent activity on the dayside, particularly in the prenoon hours, where they occur 60% of the time. Their region of excitation is uniformly distributed in radial distance and extends in local time from 0600 to 1600 but cuts off sharply at the local time boundaries. The pattern is consistent with excitation by a dayside energy source, possibly upstream waves, but the spatial distribution places constraints on models of energy transmission. (2) Fundamental toroidal resonances are observed with an occurrence rate of 40% to 50% for L > 8 at dawn but were observed less than 10% of the time at dusk for L > 8. Dusk is also the site of several types of pulsations of sufficient average intensity to obscure fundamental mode resonances, so this trend may be exaggerated by masking effects. Nonetheless, the dawn/dusk asymmetry is sufficiently remarkable to warrant further study. The occurrence distribution exhibits a pronounced node at the magnetic equator, and the occurrence rate for MLAT > 13° at dawn is ≈80%, suggesting that the fundamental mode resonances are present continually at the dawn flank. The preference for occurrence at the flank suggests that the Kelvin‐Helmholtz instability is ultimately responsible for driving the resonances. (3) Radially polarized pulsations are observed ≈10% of the time except in the 0400–1100 MLT, sector where their occurrence rate is less than 5%. The occurrence distribution of radially polarized waves suggests that they are driven by wave‐particle interactions but not by freshly injected particles. (4) Storm time Pc 5 type waves were observed most often at dusk for L > 8 where they occurred ≈30% of the time. A secondary maximum in storm time Pc 5 type occurrence near dawn was also found. The spatial distribution of storm time Pc 5 type waves suggests a relationship to substorm injections, although the secondary maximum at dawn may not be explained by this mechanism alone. (5) Quiet periods represent 30% to 50% of nighttime but less than 10% of daytime observations, while noisy periods represent ≈20% of the data at night and 40% to 50% during the day.

Quiet ionospheric currents of the southern hemisphere derived from geomagnetic records

This work describes the month‐by‐month behavior of the equivalent ionospheric current systems derived from spherical harmonic analyses of the quiet time geomagnetic field daily variations in 1965 at selected observatories representing the three southern global half‐sector regions separately encompassing South America, Africa, and Australia. These external Sq current patterns were vortices having mid‐latitude foci with midday summertime amplitudes reaching 16.2×104 A above the midnight level. The wintertime amplitudes were about 10×104 A smaller. At low latitudes there was a large intrusion of the opposite hemisphere external Sq current system into the wintertime hemisphere at prenoon hours, displacing the primary current vortex to later postnoon hours. The behavior of the southern hemisphere external currents were found to be seasonally similar to those of the northern hemisphere for the same year. The quiet year behavior was compared to the results for the 1958 active year determined earlier by Matsushita. The winter‐to‐summertime increase in focus current was found to be similar in amplitude for the 2 years. The active year summertime and equinoctial current focus amplitudes were about 2.3 times the amplitudes of corresponding months in the quiet year.