Theme: Weather and seasons

Abstract
Theme:Weather and seasons

Abstract
Many people believe that weather influences their emotional state. Along similar lines, some researchers in affective science are concerned whether testing individuals at a different time of year, a different part of the day, or in different weather conditions (e.g., in a cold and rainy morning vs. a hot evening) influences how research participants feel upon entering a study; thus inflating the measurement error. Few studies have investigated the link between baseline affective levels and the research context, such as seasonal and daily weather fluctuation in temperature, air pressure, and sunshine duration. We examined whether individuals felt more positive or negative upon entering a study by clustering data across seven laboratory experiments (total N = 1108), three seasons, and daily times ranging from 9 AM to 7 PM. We accounted for ambient temperature, air pressure, humidity, cloud cover, precipitation, wind speed, and sunshine duration. We found that only ambient temperature was a significant predictor of valence. Individuals felt more positive valence on days when it was cooler outside. However, the effect was psychologically negligible with differences between participants above c.a. 30 degrees Celsius in ambient temperature needed to generate a difference in affective valence surpassing one standard deviation. Our findings have methodological implications for studying emotions by suggesting that seasons and part of the day do not matter for baseline affective valence reported by participants, and the effects of ambient temperature are unlikely to influence most research.

Introduction
Humans engage in daily activities that elicit positive and negative affect. For instance, people perceive favorable activities—going on a trip with friends and playing in the park with the child, lying in a hammock overlooking the beach—as eliciting positive affect [1]. On the other hand, people evaluate unfavorable activities—spending the holidays alone, having a home destroyed by a tornado, being struck by lightning—as eliciting negative affect [1]. These activities are often determined by contextual factors such as weather conditions and time cycles, including seasons and days. Although the activities themselves mostly determine the emotional experience, the contextual factors also impact how positive or negative people feel in the present moment [2]. Thus, in this study, we focused on contextual factors that are believed to influence emotional affect, namely weather, seasons, and parts of the day.
As for seasons, people feel the worst in winter and feel the best in summer [3, 4]. For instance, one seasonality’s negative effect on affect is conceptualized as winter seasonal affective disorder [5]. The seasonal affective disorder is described in DSM as a variant of categorical mood disorder. However, it has been clear that the tendency of people to experience seasonal changes in mood and behavior is not limited to those severely affected but has an impact on the normal population as well. The review of epidemiological research on seasonal affective disorder found that almost in all studies, seasonal variations in mood were found with the depressive symptoms usually peaking in winter [7]. Although most studies used self-report measures in which individuals reported when they felt best or worst during the past year, others measured the mood successively across seasons and supported the mood drops in winter.
Furthermore, as almost all processes with a physiological component, affect–especially positive affect—also has diurnal cycle components. Individuals have an endogenous circadian system that operates with solar time in the day-night cycle. However, there is no consensus related to the peak of affective experience during the day, with research showing conflicting information for when people feel best throughout the day . Studies have shown that people feel the best in the morning around 11:00 , around the middle of the day, in the middle of the afternoon , and in the evenings.
Affect is also influenced by weather conditions. For instance, individuals tend to feel better when the day is less cloudy, barometric pressure is higher, precipitation lower, and wind power stronger [23]. However, more recent large-scale studies have not replicated many previous findings regarding the link between weather and emotions. For instance, contradictory effects have primarily been focused on temperature. Some researchers have found that temperature increases are associated with increased positive affect and reduced negative affect, whereas others have found the opposite.
The contradictory results may stem from not accounting for seasons and parts of the day when studying weather and affect associations. For instance, the negative association between the daily variation of affect and temperature or sunshine may be driven by the fact that people are more positive at night simply because they are not working, without any relation to lower temperature and sunshine. Furthermore, affect fluctuations related to weather conditions within a single season may not translate into the between-seasons scale. Studies have shown that affect is positively associated with air temperature and barometric pressure in spring but negatively associated in summer. Thus, in our study, we investigated whether people feel differently across time cycles (e.g., seasons) and whether the weather conditions might explain these effects.
Furthermore, the differences between the findings may also stem from differences in used methodologies. For instance, to measure participants’ mood studies used single-item questions, standardized questionnaires and automatic mood detection from social media posts . Some studies used a single report from participants whereas other employed repeated measure design with daily diaries, and experience sampling methods. Furthermore, the repeated measures lasted from reports over 11 days; 14 days, 25 days, 30 day; 90 days, to two-year period. Thus, the variety of methods may be related to the inconsistencies of the results.
Examination of how individuals feel depending on weather or point in the daily or yearly cycle is also essential for the perspective of advancing laboratory research methodology. Among concerns of experimental researchers is whether testing participants on different occasions significantly increases the noise in the measurement or produces a systematic bias. This is a special case of a more general methodological problem of whether research results are influenced by contextual (and seemingly trivial) factors, e.g., a time point in the semester among students. Thus, we focused on baseline affect among laboratory research participants. Namely, we aimed to examine whether individuals transfer any affective results of weather and time cycle into the research. If this was the case, testing individuals in more restricted conditions (e.g., at a similar part of a day or halting data collection in case of significant weather change) might improve the data quality and–possibly—reduce the type II error. If this was not the case, ignoring weather effects or time cycles might decrease the planning burden on the researcher, improve the data collection flow, and extend the time available for data collection in a project.

There is a meaningful difference between the practical methodological aim of our approach and studies that asked about the general link between weather and emotions. Most studies have been concerned with individuals’ diverse daily settings. In contrast, we focused on how individuals feel in a well-controlled laboratory environment that isolates the room environment from the outdoor environment. For instance, most researchers follow the recommendations and aim to maintain stable room temperature within the range of thermal comfort, set the constant light intensity and color temperature by covering windows and using artificial light, and reduce environmental noises (e.g., rain or wind) via the room’s sound attenuation. Consequently, this might reduce the impact of weather on affect in this specific group. Moreover, laboratory research often focuses individuals on upcoming tasks. Thus participants might be temporarily less aware of daily factors such as weather, part of day, or seasonal activities. This might even further reduce the impact of weather or time cycles on participants’ affect.